1.
Endosymbiont
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An endosymbiont or endobiont is any organism that lives within the body or cells of another organism, i. e. forming an endosymbiosis. The most common examples of obligate endosymbioses are mitochondria and chloroplasts, some human parasites, e. g. Wuchereria bancrofti and Mansonella perstans, thrive in their intermediate insect hosts because of an obligate endosymbiosis with Wolbachia spp. They can both be eliminated from said hosts by treatments that target this bacterium, however, not all endosymbioses are obligate. Also, some endosymbioses can be harmful to either of the organisms involved, two major types of organelle in eukaryotic cells, mitochondria and plastids such as chloroplasts, originated as bacterial endosymbionts. Such symbiogenesis was first suggested in 1905, and articulated by the Russian botanist Konstantin Mereschkowski in 1910 and it was reintroduced by Lynn Margulis in the 1960s. Symbiogenesis explains the origins of such as mitochondria and chloroplasts in eukaryotic cells. The theory proposes that chloroplasts and mitochondria evolved from certain types of bacteria that eukaryotic cells engulfed through endophagocytosis and these cells and the bacteria trapped inside them entered a symbiotic relationship, a close association between different types of organisms over an extended time. However, to be specific, the relationship was endosymbiotic, meaning one of the organisms lived within the other. The theory suggests that an anaerobic cell probably ingested an aerobic bacterium, the aerobic bacterium flourished within the cell because the cells cytoplasm was abundant in half-digested food molecules. The bacterium digested these molecules with oxygen and gained great amounts of energy, because the bacterium had so much energy, it probably leaked some of it as adenosine triphosphate into the cells cytoplasm. This benefited the anaerobic cell because it was now able to breathe aerobically, eventually, the aerobic bacterium could no longer live independently from the cell, and it, therefore, became a mitochondrion. The origin of the chloroplast is very similar to that of the mitochondrion, a cell must have captured a photosynthetic cyanobacterium and failed to digest it. The cyanobacterium thrived in the cell and eventually evolved into the first chloroplast, there are several lines of evidence that support endosymbiosis theory. Mitochondria and chloroplasts contain their own supply of DNA, which may be remnants of the genome the organelles had when they were independent aerobic bacteria. The single most convincing evidence of the descent of organelles from bacteria is the position of mitochondria, mitochondria have sequences that clearly indicate origin from a group of bacteria called the alphaproteobacteria. Plastids have DNA sequences that indicate origin from the cyanobacteria, in addition, there are organisms alive today, called living intermediates, that are in a similar endosymbiotic condition to the prokaryotic cells and the aerobic bacteria. Living intermediates show that the proposed by the endosymbiont theory is possible. For example, the giant amoeba Pelomyxa lacks mitochondria but has aerobic bacteria that carry out a similar role, a variety of corals, clams, snails, and one species of Paramecium permanently host algae in their cells
2.
Mitochondrion
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The mitochondrion is a double membrane-bound organelle found in all eukaryotic organisms. Some cells in multicellular organisms may however lack them. A number of organisms, such as microsporidia, parabasalids. To date, only one eukaryote, Monocercomonoides, is known to have completely lost its mitochondria, the word mitochondrion comes from the Greek μίτος, mitos, thread, and χονδρίον, chondrion, granule or grain-like. Mitochondria generate most of the supply of adenosine triphosphate, used as a source of chemical energy. Mitochondria are commonly between 0.75 and 3 μm in diameter but vary considerably in size and structure, unless specifically stained, they are not visible. Mitochondrial biogenesis is in turn temporally coordinated with these cellular processes, Mitochondria have been implicated in several human diseases, including mitochondrial disorders, cardiac dysfunction, heart failure and autism. The number of mitochondria in a cell can vary widely by organism, tissue, for instance, red blood cells have no mitochondria, whereas liver cells can have more than 2000, The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the space, the inner membrane. Although most of a cells DNA is contained in the cell nucleus, mitochondrial proteins vary depending on the tissue and the species. In humans,615 distinct types of protein have been identified from cardiac mitochondria, the mitochondrial proteome is thought to be dynamically regulated. The first observations of structures that probably represented mitochondria were published in the 1840s. Richard Altmann, in 1890, established them as cell organelles, the term mitochondria was coined by Carl Benda in 1898. Leonor Michaelis discovered that Janus green can be used as a stain for mitochondria in 1900. Benjamin F. Kingsbury, in 1912, first related them with cell respiration, in 1913, particles from extracts of guinea-pig liver were linked to respiration by Otto Heinrich Warburg, which he called grana. Warburg and Heinrich Otto Wieland, who had postulated a similar particle mechanism. It was not until 1925, when David Keilin discovered cytochromes, in the following years, the mechanism behind cellular respiration was further elaborated, although its link to the mitochondria was not known. The introduction of tissue fractionation by Albert Claude allowed mitochondria to be isolated from other cell fractions, in 1946, he concluded that cytochrome oxidase and other enzymes responsible for the respiratory chain were isolated to the mitchondria
3.
Proteobacteria
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The Proteobacteria are a major phylum of Gram-negative bacteria. The name of the phylum has never been published as no type genus has been proposed. They include a variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, Yersinia. Others are free-living, and include many of the responsible for nitrogen fixation. Carl Woese established this grouping in 1987, calling it informally the purple bacteria, the Alphaproteobacteria grow at very low levels of nutrients and have unusual morphology such as stalks and buds. They include agriculturally important bacteria capable of inducing nitrogen fixation in symbiosis with plants, the type order is the Caulobacterales, comprising stalk-forming bacteria such as Caulobacter. The Betaproteobacteria are highly diverse and contain chemolithoautotrophs, photoautotrophs. The type order is the Burkholderiales, comprising a range of metabolic diversity. The Gammaproteobacteria are the largest class in terms of species with validly published names, the type order is the Pseudomonadales, which include the genera Pseudomonas and the nitrogen-fixing Azotobacter. The Deltaproteobacteria include bacteria that are predators on other bacteria and are important contributors to the side of the sulfur cycle. The type order is the Myxococcales, which includes organisms with self-organising abilities such as Myxococcus spp, the Epsilonproteobacteria are often slender, Gram-negative rods that are helical or curved. The type order is the Campylobacterales, which includes important food pathogens such as Campylobacter spp, the type order is the Oligoflexales, which contains the genus Oligoflexus. The Acidithiobacillia contain only sulfur-oxidising autotrophs, the type order is the Acidithiobacillales, which includes economically important organisms used in the mining industry such as Acidithiobacillus spp. All Proteobacteria are Gram-negative, though some may stain Gram-positive or Gram-variable in practice, many move about using flagella, but some are nonmotile or rely on bacterial gliding. The last include the Myxobacteriales, an order of bacteria that can aggregate to form fruiting bodies. Also, a variety in the types of metabolism exists. Most members are facultatively or obligately anaerobic, Chemolithoautotrophic, and heterotrophic, a variety of genera, which are not closely related to each other, convert energy from light through photosynthesis. Proteobacteria are associated with the imbalance of microbiota of the reproductive tract of women
4.
Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
5.
Prokaryote
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A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek πρό before and καρυόν nut or kernel, prokaryotes can be divided into two domains, Archaea and bacteria. In contrast, species with nuclei and organelles are placed in the domain Eukaryota, in the prokaryotes, all the intracellular water-soluble components are located together in the cytoplasm enclosed by the cell membrane, rather than in separate cellular compartments. Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells, some prokaryotes, such as cyanobacteria may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles, molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species. Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus, the division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization. Distinctive types of prokaryotes include extremophiles and methanogens, these are common in extreme environments. Prokaryotes have a cytoskeleton, albeit more primitive than that of the eukaryotes. At least some also contain intracellular structures that can be seen as primitive organelles. Membranous organelles are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, in addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles. Most prokaryotes are between 1 µm and 10 µm, but they can vary in size from 0.2 µm to 750 µm, Bacteria and archaea reproduce through asexual reproduction, usually by binary fission. DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has mainly studied in bacteria. In bacteria, gene transfer occurs by three processes and these are bacterial virus -mediated transduction, plasmid-mediated conjugation, and natural transformation. Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, the transfer of bacterial DNA is under the control of the bacteriophage’s genes rather than bacterial genes. Conjugation in the well-studied E. coli system is controlled by plasmid genes, infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA also appears to be a process rather than a bacterial adaptation. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium, for a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called competence. About 40 genes are required in Bacillus subtilis for the development of competence, the length of DNA transferred during B. subtilis transformation can be as much as a third to the whole chromosome
6.
Russians
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Russians are an East Slavic ethnic group native to Eastern Europe. The majority of Russians inhabit the state of Russia, while notable minorities exist in Ukraine, Kazakhstan. A large Russian diaspora exists all over the world, with numbers in the United States, Germany, Israel. Russians are the most numerous group in Europe. They are predominantly Orthodox Christians by religion, the Russian language is official in Russia, Belarus, Kazakhstan, Kyrgyzstan, and Tajikistan, and also spoken as a secondary language in many former Soviet states. There are two Russian words which are translated into English as Russians. One is русские, which most often means ethnic Russians, another is россияне, which means citizens of Russia. The former word refers to ethnic Russians, regardless of what country they live in, under certain circumstances this term may or may not extend to denote members of other Russian-speaking ethnic groups from Russia, or from the former Soviet Union. The latter word refers to all people holding citizenship of Russia, regardless of their ethnicity, translations into other languages often do not distinguish these two groups. The name of the Russians derives from the Rus people, the name Rus would then have the same origin as the Finnish and Estonian names for Sweden, Ruotsi and Rootsi. According to other theories the name Rus is derived from Proto-Slavic *roud-s-ь, the modern Russians formed from two groups of East Slavic tribes, Northern and Southern. The tribes involved included the Krivichs, Ilmen Slavs, Radimichs, Vyatiches, genetic studies show that modern Russians do not differ significantly from Belarusians and Ukrainians. Some ethnographers, like Zelenin, affirm that Russians are more similar to Belarusians, such Uralic peoples included the Merya and the Muromians. Outside archaeological remains, little is known about the predecessors to Russians in general prior to 859 AD when the Primary Chronicle starts its records and it is thought that by 600 AD, the Slavs had split linguistically into southern, western, and eastern branches. Later, both Belarusians and South Russians formed on this ethnic linguistic ground, the same Slavic ethnic population also settled the present-day Tver Oblast and the region of Beloozero. With the Uralic substratum, they formed the tribes of the Krivichs, in 2010, the worlds Russian population was 129 million people of which 86% were in Russia,11. 5% in the CIS and Baltic countries, with a further 2. 5% living in other countries. Roughly 111 million ethnic Russians live in Russia, 80% of whom live in the European part of Russia, ethnic Russians historically migrated throughout the area of former Russian Empire and Soviet Union, sometimes encouraged to re-settle in borderlands by the Tsarist and later Soviet government. On some occasions ethnic Russian communities, such as Lipovans who settled in the Danube delta or Doukhobors in Canada, after the Russian Revolution and Russian Civil War starting in 1917, many Russians were forced to leave their homeland fleeing the Bolshevik regime, and millions became refugees
7.
Konstantin Mereschkowski
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He was inspired by his work as a leading lichenologist – lichens were of major interest at the time as it had recently been shown that they exhibit a symbiotic relationship between fungi and algae. Around the turn of the century he collected a sizeable lichen herbarium, containing over 2000 specimens from lands in Russia, Austria, the collection is currently in the possession of Kazan University. He did not believe that natural selection could explain biological novelty, positing instead the acquisition and he was criticised by another Russian lichenologist, Alexandr Alexandrovich Elenkin. Merezhovskys ideas of symbiogenesis are reflected in the endosymbiotic theory developed and popularised by Lynn Margulis. This argues that such as chloroplasts and mitochondria are the descendants of bacteria that evolved into an intracellular symbiosis with early eukaryotic cells. Merezhkovsky, also wrote stories, such as The paradise on earth or a winter night dream
8.
Lynn Margulis
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Lynn Margulis was an American evolutionary theorist, science author, educator, and popularizer, and was the primary modern proponent for the significance of symbiosis in evolution. Historian Jan Sapp has said that Lynn Marguliss name is as synonymous with symbiosis as Charles Darwins is with evolution. Throughout her career, Margulis work could arouse intense objection, and her paper, On the Origin of Mitosing Cells. Margulis was elected a member of the US National Academy of Sciences in 1983, President Bill Clinton presented her the National Medal of Science in 1999. The Linnean Society of London awarded her the Darwin-Wallace Medal in 2008, called Sciences Unruly Earth Mother, a vindicated heretic, or a scientific rebel, Margulis was a strong critic of neo-Darwinism. Her position sparked lifelong debate with leading neo-Darwinian biologists, including Richard Dawkins, many of her major works, particularly those intended for a general readership, were collaboratively written with her son Dorion Sagan. Lynn Margulis was born in Chicago, to a Jewish, Zionist family and her parents were Morris Alexander and Leona Wise Alexander. She was the eldest of four daughters and her father was an attorney who also ran a company that made road paints. Her mother operated a travel agency and she entered the Hyde Park Academy High School in 1952, describing herself as a bad student who frequently had to stand in the corner. She joined the University of Wisconsin to study biology under Hans Ris and Walter Plaut, her supervisor and she then pursued research at the University of California, Berkeley, under the zoologist Max Alfert. Before she could complete her dissertation, she was offered research associateship and it was while working there that she obtained her PhD from the University of California, Berkeley in 1965. Her thesis was An Unusual Pattern of Thymidine Incorporation in Euglena, in 1966 she moved to Boston University, where she taught biology for twenty-two years. She was initially an Adjunct Assistant Professor, and appointed to Assistant Professor in 1967 and she was promoted to Associate Professor in 1971, to full Professor in 1977, and to University Professor in 1986. In 1988 she was appointed Distinguished Professor of Botany at the University of Massachusetts at Amherst and she was Distinguished Professor of Biology in 1993. In 1997 she transferred to the Department of Geosciences at Amherst to become Distinguished Professor of Geosciences with great delight, Margulis married astronomer Carl Sagan in 1957 soon after she got her bachelors degree. Sagan was then a student in physics at the University of Chicago. Their marriage ended in 1964, just before she completed her PhD and they had two sons, Dorion Sagan, who later became a popular science writer and her collaborator, and Jeremy Sagan, software developer and founder of Sagan Technology. In 1967, she married Thomas N. Margulis, a crystallographer and they had a son Zachary Margulis-Ohnuma, New York City criminal defense lawyer, and a daughter Jennifer Margulis, teacher and author
9.
Organelle
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In cell biology, an organelle is a specialized subunit within a cell that has a specific function. Individual organelles are usually enclosed within their own lipid bilayers. The name organelle comes from the idea that these structures are to cells what an organ is to the body, organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells, while prokaryotes do not possess organelles per se, some do contain protein-based bacterial microcompartments, which are thought to act as primitive organelles. In biology organs are defined as confined functional units within an organism, the analogy of bodily organs to microscopic cellular substructures is obvious, as from even early works, authors of respective textbooks rarely elaborate on the distinction between the two. In the 1830s, Félix Dujardin refuted Ehrenberg theory which said that microorganims have the organs of multicellular animals. Credited as the first to use a diminutive of organ for cellular structures was German zoologist Karl August Möbius, under this definition, there would only be two broad classes of organelles, mitochondria plastids. Other organelles are also suggested to have endosymbiotic origins, but do not contain their own DNA, under the more restricted definition of membrane-bound structures, some parts of the cell do not qualify as organelles. Nevertheless, the use of organelle to refer to non-membrane bound structures such as ribosomes is common and this has led some texts to delineate between membrane-bound and non-membrane bound organelles. The larger organelles, such as the nucleus and vacuoles, are visible with the light microscope. They were among the first biological discoveries made after the invention of the microscope, not all eukaryotic cells have each of the organelles listed below. Exceptional organisms have cells that do not include some organelles that might otherwise be considered universal to eukaryotes, there are also occasional exceptions to the number of membranes surrounding organelles, listed in the tables below. In addition, the number of organelles of each type found in a given cell varies depending upon the function of that cell. This idea is supported in the Endosymbiotic theory, in the past, they were often viewed as having little internal organization, but slowly, details are emerging about prokaryotic internal structures. However, more recent research has revealed that at least some prokaryotes have microcompartments such as carboxysomes and these subcellular compartments are 100–200 nm in diameter and are enclosed by a shell of proteins. The function of a protein is correlated with the organelle in which it resides. CoRR Hypothesis Ejectosome Endosymbiotic theory Organelle biogenesis Membrane vesicle trafficking Host-pathogen interface Tree of Life project, Eukaryotes
10.
Symbiosis
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Symbiosis is any type of a close and long-term biological interaction between two different species, be it mutualistic, commensalistic, or parasitic. In 1879, Heinrich Anton de Bary defined it as the living together of unlike organisms, Symbiosis can be obligatory, which means that one or both of the symbionts entirely depend on each other for survival, or facultative when they can generally live independently. When one organism lives on another such as mistletoe, it is called ectosymbiosis, or endosymbiosis when one partner lives inside the tissues of another, as in Symbiodinium in corals. In 1877, Albert Bernhard Frank used the term symbiosis which previously had used to depict people living together in community to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as the living together of unlike organisms, symbiotic relationships can be obligate, meaning that one or both of the symbionts entirely depend on each other for survival. For example, in lichens, which consist of fungal and photosynthetic symbionts, the algal or cyanobacterial symbionts in lichens, such as Trentepohlia, can generally live independently, and their symbiosis is, therefore, facultative. Endosymbiosis is any relationship in which one symbiont lives within the tissues of the other, either within the cells or extracellularly. Mutualism or interspecies reciprocal altruism is a relationship between individuals of different species where both individuals benefit, in general, only lifelong interactions involving close physical and biochemical contact can properly be considered symbiotic. Mutualistic relationships may be either obligate for both species, obligate for one but facultative for the other, or facultative for both, a large percentage of herbivores have mutualistic gut flora to help them digest plant matter, which is more difficult to digest than animal prey. This gut flora is made up of cellulose-digesting protozoans or bacteria living in the herbivores intestines, coral reefs are the result of mutualisms between coral organisms and various types of algae which live inside them. Most land plants and land ecosystems rely on mutualisms between the plants, which fix carbon from the air, and mycorrhyzal fungi, which help in extracting water, an example of mutual symbiosis is the relationship between the ocellaris clownfish that dwell among the tentacles of Ritteri sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protect the clownfish from its predators, a special mucus on the clownfish protects it from the stinging tentacles. A further example is the fish, which sometimes lives together with a shrimp. The shrimp digs and cleans up a burrow in the sand in which both the shrimp and the fish live. The shrimp is almost blind, leaving it vulnerable to predators when outside its burrow, in case of danger the goby fish touches the shrimp with its tail to warn it. When that happens both the shrimp and goby fish quickly retreat into the burrow, different species of gobies also exhibit mutualistic behavior through cleaning up ectoparasites in other fish. Another non-obligate symbiosis is known from encrusting bryozoans and hermit crabs, the bryozoan colony develops a cirumrotatory growth and offers the crab a helicospiral-tubular extension of its living chamber that initially was situated within a gastropod shell. A spectacular examples of mutualism is between the siboglinid tube worms and symbiotic bacteria that live at hydrothermal vents and cold seeps
11.
Bacteria
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Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods, Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology, There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants, Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of bodies and bacteria are responsible for the putrefaction stage in this process. In March 2013, data reported by researchers in October 2012, was published and it was suggested that bacteria thrive in the Mariana Trench, which with a depth of up to 11 kilometres is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, You can find microbes everywhere—theyre extremely adaptable to conditions, the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial particularly in the gut flora. However several species of bacteria are pathogenic and cause diseases, including cholera, syphilis, anthrax, leprosy. The most common fatal diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year. In developed countries, antibiotics are used to treat infections and are also used in farming, making antibiotic resistance a growing problem. Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and these evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. In 2008, fossils of macroorganisms were discovered and named as the Francevillian biota, however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea, here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea
12.
Archaea
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The Archaea constitute a domain and kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles in their cells, Archaea were initially classified as bacteria, receiving the name archaebacteria, but this classification is outdated. Archaeal cells have unique properties separating them from the two domains of life, Bacteria and Eukaryota. The Archaea are further divided into multiple recognized phyla, classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment. Archaea and bacteria are generally similar in size and shape, although a few archaea have very strange shapes, such as the flat, other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. Archaea use more energy sources than eukaryotes, these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea use sunlight as a source, and other species of archaea fix carbon, however, unlike plants and cyanobacteria. Archaea reproduce asexually by fission, fragmentation, or budding, unlike bacteria and eukaryotes. They are also found in the colon, oral cavity. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet, Archaea are a major part of Earths life and may play roles in both the carbon cycle and the nitrogen cycle. No clear examples of archaeal pathogens or parasites are known, one example is the methanogens that inhabit human and ruminant guts, where their vast numbers aid digestion. Methanogens are also used in production and sewage treatment, and enzymes from extremophile archaea that can endure high temperatures. For much of the 20th century, prokaryotes were regarded as a group of organisms and classified based on their biochemistry, morphology. For example, microbiologists tried to classify based on the structures of their cell walls, their shapes. In 1965, Emile Zuckerkandl and Linus Pauling proposed instead using the sequences of the genes in different prokaryotes to work out how they are related to each other and this approach, known as phylogenetics, is the main method used today. Archaea were first classified as a group of prokaryotes in 1977 by Carl Woese. These two groups were named the Archaebacteria and Eubacteria and treated as kingdoms or subkingdoms, which Woese. Woese argued that group of prokaryotes is a fundamentally different sort of life
13.
Plastid
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The plastid is a major double-membrane organelle found, among others, in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell and they often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cells color. They have an evolutionary origin and possess a double-stranded DNA molecule that is circular. Those plastids that contain chlorophyll can carry out photosynthesis, Plastids can also store products like starch and can synthesise fatty acids and terpenes, which can be used for producing energy and as raw material for the synthesis of other molecules. For example, the components of the plant cuticle and its epicuticular wax are synthesized by the cells from palmitic acid. All plastids are derived from proplastids, which are present in the regions of the plant. Proplastids and young chloroplasts commonly divide by fission, but more mature chloroplasts also have this capacity. In plants, plastids may differentiate into several forms, depending upon which function they play in the cell, each plastid creates multiple copies of a circular 75–250 kilobase plastome. The plastome contains about 100 genes encoding ribosomal and transfer ribonucleic acids as well as involved in photosynthesis. However, these only represent a small fraction of the total protein set-up necessary to build and maintain the structure. Plastid DNA exists as large protein-DNA complexes associated with the envelope membrane. Each nucleoid particle may contain more than 10 copies of the plastid DNA, the proplastid contains a single nucleoid located in the centre of the plastid. The developing plastid has many nucleoids, localized at the periphery of the plastid, during the development of proplastids to chloroplasts, and when plastids convert from one type to another, nucleoids change in morphology, size and location within the organelle. The remodelling of nucleoids is believed to occur by modifications to the composition, many plastids, particularly those responsible for photosynthesis, possess numerous internal membrane layers. In plant cells, long thin protuberances called stromules sometimes form and extend from the main body into the cytosol. Proteins, and presumably smaller molecules, can move within stromules, most cultured cells that are relatively large compared to other plant cells have very long and abundant stromules that extend to the cell periphery. In 2014, evidence of possible plastid genome loss was found in Rafflesia lagascae, a non-photosynthetic parasitic flowering plant, and in Polytomella, extensive searches for plastid genes in both Rafflesia and Polytomella yielded no results, however the conclusion that their plastomes are entirely missing is still controversial. Some scientists argue that plastid genome loss is unlikely since even non-photosynthetic plastids contain genes necessary to complete various biosynthetic pathways, in algae, the term leucoplast is used for all unpigmented plastids and their function differs from the leucoplasts of plants
14.
Chloroplast
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Chloroplasts /ˈklɔːrəˌplæsts, -plɑːsts/ are organelles, specialized subunits, in plant and algal cells. Their discovery inside plant cells is usually credited to Julius von Sachs and they then use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of functions, including fatty acid synthesis, much amino acid synthesis. The number of chloroplasts per cell varies from one, in algae, up to 100 in plants like Arabidopsis. A chloroplast is a type of known as a plastid. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll, chloroplasts are highly dynamic—they circulate and are moved around within plant cells, and occasionally pinch in two to reproduce. Their behavior is influenced by environmental factors like light color. Chloroplasts, like mitochondria, contain their own DNA, which is thought to be inherited from their ancestor—a photosynthetic cyanobacterium that was engulfed by a eukaryotic cell. Chloroplasts cannot be made by the plant cell and must be inherited by each cell during cell division. With one exception, all chloroplasts can probably be traced back to a single endosymbiotic event, despite this, chloroplasts can be found in an extremely wide set of organisms, some not even directly related to each other—a consequence of many secondary and even tertiary endosymbiotic events. The word chloroplast is derived from the Greek words chloros, which means green, and plastes, the first definitive description of a chloroplast was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, A. F. W. Schimper would name these bodies as chloroplastids, in 1884, Eduard Strasburger adopted the term chloroplasts. Chloroplasts are one of many types of organelles in the plant cell and they are considered to have originated from cyanobacteria through endosymbiosis—when a eukaryotic cell engulfed a photosynthesizing cyanobacterium that became a permanent resident in the cell. Mitochondria are thought to have come from an event, where an aerobic prokaryote was engulfed. This origin of chloroplasts was first suggested by the Russian biologist Konstantin Mereschkowski in 1905 after Andreas Schimper observed in 1883 that chloroplasts closely resemble cyanobacteria, chloroplasts are only found in plants, algae, and the amoeboid Paulinella chromatophora. Cyanobacteria are considered the ancestors of chloroplasts and they are sometimes called blue-green algae even though they are prokaryotes. They are a phylum of bacteria capable of carrying out photosynthesis. Cyanobacteria also contain a cell wall, which is thicker than in other gram-negative bacteria
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Rickettsiales
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The Rickettsiales, also called rickettsias, are an order of small proteobacteria. Most of those described survive only as endosymbionts of other cells, some are notable pathogens, including Rickettsia, which causes a variety of diseases in humans. On the other end of the scale, genetic studies support the theory according to which mitochondria. Some have also speculated that viruses might have developed from them, the Rickettsiales are among the most mysterious groups of Proteobacteria, owing largely to difficulties in cultivating them. The group includes all obligate endosymbiont bacteria, however, a number of species have been removed, such as Coxiella burnetii, the cause of Q fever. The Rickettsiales has an order the Pelagibacterales, which is composed of free living bacteria with extremely streamlined genomes. The relation between the two order is retained in the subclass, the Rickettsidae, which include the Rickettsiales, the Pelagibacteriales and the extinct protomitochondrion
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Cyanobacteria
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The name cyanobacteria comes from the color of the bacteria. Sometimes, they are called blue-green algae, and incorrectly so, because cyanobacteria are prokaryotes, like other prokaryotes, cyanobacteria have no membrane-sheathed organelles. Photosynthesis is performed in distinctive folds in the membrane of the cell. Biologists commonly agree that chloroplasts found in eukaryotes have their ancestry in cyanobacteria, via a process called endosymbiosis, Cyanobacteria are a group of photosynthetic, nitrogen fixing bacteria that live in a wide variety of habitats such as moist soils and in water. They may be free-living or form relationships with plants or with lichen-forming fungi as in the lichen genus Peltigera. They range from unicellular to filamentous and include colonial species, colonies may form filaments, sheets, or even hollow balls. Cyanobacteria can fix nitrogen in anaerobic conditions by means of specialized cells called heterocysts. Heterocysts may also form under the environmental conditions when fixed nitrogen is scarce. Free-living cyanobacteria are present in the column in rice paddies, and cyanobacteria can be found growing as epiphytes on the surfaces of the green alga, Chara. Cyanobacteria such as, can provide rice plantations with biofertilizer, many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere. The cells in a hormogonium are often thinner than in the state. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, each individual cell of a cyanobacterium typically has a thick, gelatinous cell wall. They lack flagella, but hormogonia of some species can move about by gliding along surfaces, many of the multicellular filamentous forms of Oscillatoria are capable of a waving motion, the filament oscillates back and forth. In water columns, some cyanobacteria float by forming gas vesicles and these vesicles are not organelles as such. They are not bounded by membranes, but by a protein sheath. Cyanobacteria can be found in almost every terrestrial and aquatic habitat—oceans, fresh water, damp soil, temporarily moistened rocks in deserts, bare rock and soil and they can occur as planktonic cells or form phototrophic biofilms. They are found in almost every endolithic ecosystem, a few are endosymbionts in lichens, plants, various protists, or sponges and provide energy for the host. Some live in the fur of sloths, providing a form of camouflage, aquatic cyanobacteria are known for their extensive and highly visible blooms that can form in both freshwater and marine environments
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Fission (biology)
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In biology, fission is the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original. The object experiencing fission is usually a cell, but the term may refer to how organisms, bodies, populations. The fission may be binary fission, in which a single entity produces two parts, or multiple fission, in which a single entity produces multiple parts, organisms in the domains of Archaea and Bacteria reproduce with binary fission. This form of reproduction and cell division is also used by some organelles within eukaryotic organisms. Binary fission results in the reproduction of a prokaryotic cell by dividing the cell into two parts, each with the potential to grow to the size of the original. Unlike the process of mitosis used by cells, binary fission takes place without the formation of a spindle apparatus in the cell. The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane, when the cell begins to pull apart, the replicated and original chromosomes are separated. The consequence of this method of reproduction is that all the cells are genetically identical. The process of fission in bacteria involves the following steps. First, the cells DNA is replicated, the replicated DNA copies then move to opposite poles of the cell in an energy-dependent process. Then, the plate of the cell constricts and separates the plasma membrane such that each new cell has exactly the same genetic material. More specifically, the following occur, The bacterium before binary fission is when the DNA is tightly coiled. The DNA of the bacterium has uncoiled and duplicated, the DNA is pulled to the separate poles of the bacterium as it increases size to prepare for splitting. The growth of a new cell wall begins to separate the bacterium, the new cell wall fully develops, resulting in the complete split of the bacterium. The new daughter cells have tightly coiled DNA rods, ribosomes, and plasmids, binary fission is generally rapid though its speed varies between species. For E. coli, cells typically divide about every 20 minutes at 37 °C and this time period can therefore be referred to as the doubling time. Some species other than E. coli may have faster or slower doubling times, some organelles in eukaryotic cells reproduce using binary fission. Mitochondrial fission occurs frequently within the cell, even when the cell is not actively undergoing mitosis, binary fission in organisms can occur in four ways, irregular, longitudinal, transverse, oblique
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Porin (protein)
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Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. Unlike other membrane proteins, porins are large enough to allow passive diffusion. They are present in the membrane of gram-negative bacteria and some gram-positive bacteria of the group Mycolata, the mitochondria. Porins are composed of β strands, which are, in general, linked together by beta turns on the cytoplasmic side, the β strands lie in an antiparallel fashion and form a cylindrical tube, called a β barrel. The amino acid composition of the porin β strands are unique in that polar and nonpolar residues alternate along them, the porin channel is partially blocked by a loop, called the eyelet, which projects into the cavity. In general, it is found between strands 5 and 6 of each barrel, and it defines the size of solute that can traverse the channel. It is lined almost exclusively with charged amino acids arranged on opposite sides of the channel, to transport medium-sized or charged molecules across, the molecules move through a porin, a water-filled channel or pore. Porins typically control the diffusion of small metabolites like sugars, ions, porins are chemically selective – transporting only one group of molecules – or may be specific for one molecule. Beta-lactam and fluoroquinolone antibiotics must pass through porins to reach their targets in gram negative bacteria, bacteria can develop resistance to these antibiotics by mutating the gene that encodes the porin – the antibiotics are then excluded from passing through the outer membrane. The term nucleoporin refers to completely unrelated proteins facilitating transport through nuclear pores in the nuclear envelope, the discovery of porins has been attributed to Hiroshi Nikaido, nicknamed the porinologist. There are five evolutionarily independent superfamilies of porins, porin superfamily I includes 47 families of porins with a range of numbers of trans-membrane β-strands. These include the GBP, SP and RPP porin families, while PSF I includes 47 families, PSF II-V each contain only 2 families. While PSF I derives members from gram-negative bacteria primarily one family of eukaryotic mitochondrial porins, PSF II, PSF III and V are derived from eukaryotic organelle
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Cardiolipin
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Cardiolipin is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid composition. It can also be found in the membranes of most bacteria, the name ‘cardiolipin’ is derived from the fact that it was first found in animal hearts. It was first isolated from beef heart in the early 1940s, Cardiolipin is a kind of diphosphatidylglycerol lipid. Two phosphatidic acid moieties connect with a backbone in the center to form a dimeric structure. So it has four groups and potentially carries two negative charges. As there are four distinct alkyl chains in cardiolipin, the potential for complexity of this species is enormous. However, in most animal tissues, cardiolipin contains 18-carbon fatty alkyl chains with 2 unsaturated bonds on each of them and it has been proposed that the 4 acyl chain configuration is an important structural requirement for the high affinity of CL to inner membrane proteins in mammalian mitochondria. However, studies with isolated enzyme preparations indicate that its importance may vary depending on the protein examined, since there are two phosphates in the molecule, each of them can catch one proton. Although it has a structure, ionizing one phosphate happens at a very different levels of acidity than ionizing both, pK1 =3 and pK2 >7.5. So under normal conditions, the molecule may carry only one negative charge. The hydroxyl groups on phosphate would form an intramolecular hydrogen bond with the centered glycerol’s hydroxyl group. This structure traps one proton, which is helpful for oxidative phosphorylation. As the head group forms such compact bicycle structure, the group area is quite small relative to the big tail region consisting of 4 acyl chains. Based on this structure, the fluorescent mitochondrial indicator, nonyl acridine orange was introduced in 1982. NAO has a large head and small tail structure which can compensate with cardiolipin’s small head large tail structure. Several studies were published utilizing NAO both as a quantitative mitochondrial indicator and an indicator of CL content in mitochondria. However, NAO is influenced by membrane potential and/or the spatial arrangement of CL, but NAO still represents a simple method of assessing CL content. Cardiolipin has a weight of 1466.0585 g/mol
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Nucleus (cell)
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In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. Cell nuclei contain most of the genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones. The genes within these chromosomes are the nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, because the nuclear membrane is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules. Movement of large molecules such as proteins and RNA through the pores is required for gene expression and the maintenance of chromosomes. The best-known of these is the nucleolus, which is involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA, the nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek and he observed a lumen, the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei, the nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area and he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the plays a role in generating cells. He believed that he had observed new cells assembling around cytoblasts, Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The function of the nucleus remained unclear, between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a nucleated cell, therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other groups, including amphibians. Eduard Strasburger produced the results for plants in 1884
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Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
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Andreas Franz Wilhelm Schimper
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Andreas Franz Wilhelm Schimper was a German botanist and phytogeographer who made major contributions in the fields of histology, ecology and plant geography. He travelled to South East Asia and the Caribbean as part of the 1899 deep-sea expedition and his health had been seriously affected by malaria and he died of complications at the age of only 45 years in 1901. He coined the terms tropical rainforest and sclerophyll and is commemorated in numerous specific names, Schimper was born in Strassburg, into a family of eminent scientists. His father Wilhelm Philippe Schimper was Director of the Natural History Museum in Strassburg, Professor of Geology, and his fathers cousin was Georg Wilhelm Schimper, prominent collector and explorer in Arabia and North Africa and the naturalist Karl Friedrich Schimper. Schimper studied at the University of Strassburg from 1874 to 1878, thereafter, he worked in Lyon and in 1880 travelled to the United States, becoming a Fellow at Johns Hopkins University in Baltimore, Massachusetts. In 1882, he moved back to the University of Bonn working with Eduard Strasburger, in 1883, Schimper postulated the endosymbiotic origin of chloroplasts and paved the way to the Endosymbiont theory of Konstantin Mereschkowski und Lynn Margulis. In 1886, he was appointed Extraordinary Professor at the University of Bonn and he had become interested in phytogeography and plant ecology, undertaking expeditions to the West Indies and Venezuela in 1882-1883. In 1886, he stayed with Fritz Müller in Brazil, and in 1889-1890 in Ceylon and this resulted in his account of the Rhizophoraceae in Engler & Prantls Natürliche Pflanzenfamilien. In 1898, he accepted the appointment of Professor of Botany at the University of Basel and this was a deep-sea expedition aboard the SS Valdivia under the leadership of Professor Carl Chun. Returning in 1899, he took up the appointment of Professor of Botany at the University of Basel and his health had been seriously affected by malaria contracted in Cameroon and Dar-es-Salaam, and he died of complications of malaria at the age of only 45 years in 1901. In this book he coined the terms tropical rainforest and sclerophyll, in 1894, Schimper was one of the 4 original authors of the textbook of botany Lehrbuch der Botanik and until the 5th edition 1902 editor of the chapter spermatophyta or seed-bearing plants. Rudolf Marloth wrote an account of the Cape floral region for Chuns proposed Wissenschaftliche Ergebnisse der deutschen Tiefsee-Expedition auf dem Dampfer Valdivia 1898-1899, and Schimper contributed two chapters on Gebiet der Hartlaubgehölze and Der Knysnawald. Schimper is commemorated in numerous specific names, in 1892, he was voted a member of the Deutsche Akademie der Naturforscher Leopoldina gewählt. Works by Andreas Franz Wilhelm Schimper at Project Gutenberg Works by or about Andreas Franz Wilhelm Schimper at Internet Archive Books by, Schimper,1903 Biodiversity Heritage Library Botanical Exploration of Southern Africa Mary Gunn & LE Codd
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Mutualism (biology)
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Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits from the activity of the other. Similar interactions within a species are known as co-operation, symbiosis involves two species living in close proximity and includes relationships that are mutualistic, parasitic, and commensal. Symbiotic relationships are sometimes, but not always, mutualistic, a well-known example of mutualism is the relationship between ungulates and bacteria within their intestines. The ungulates benefit from the produced by the bacteria, which facilitates digestion. This can also be found in many different symbiotic relationships. Mutualism plays a key part in ecology, in addition, mutualism is thought to have driven the evolution of much of the biological diversity we see, such as flower forms and co-evolution between groups of species. However mutualism has historically received less attention than other such as predation. It is therefore common to categorise mutualisms according to the closeness of the association, using such as obligate. Defining closeness, however, is also problematic and it can refer to mutual dependency or the biological intimacy of the relationship in relation to physical closeness. The term mutualism was introduced by Pierre-Joseph van Beneden in 1876, other examples include rhizobia bacteria that fix nitrogen for leguminous plants in return for energy-containing carbohydrates. Pollination in which nectar or pollen are traded for pollen dispersal or ant protection of aphids, phagophiles feed on ectoparasites, thereby providing anti-pest service, as in cleaning symbiosis. Elacatinus and Gobiosoma, genus of gobies, also feed on ectoparasites of their clients while cleaning them, zoochory is the dispersal of the seeds of plants by animals. This is similar to pollination in that the plant produces food resources for animals that disperse the seeds, strict service-service interactions are very rare, for reasons that are far from clear. Therefore, what appears to be a service-service mutualism in fact has a service-resource component, a second example is that of the relationship between some ants in the genus Pseudomyrmex and trees in the genus Acacia, such as the whistling thorn and bullhorn acacia. The ants nest inside the plants thorns, in exchange for shelter, the ants protect acacias from attack by herbivores and competition from other plants by trimming back vegetation that would shade the acacia. In addition, another component is present, as the ants regularly feed on lipid-rich food-bodies called Beltian bodies that are on the Acacia plant. In the neotropics, the ant, Myrmelachista schumanni makes its nest in cavities in Duroia hirsute. Plants in the vicinity that belong to other species are killed with formic acid and this selective gardening can be so aggressive that small areas of the rainforest are dominated by Duroia hirsute
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Symbiogenesis
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It holds that the organelles distinguishing eukaryote cells evolved through symbiosis of individual single-celled prokaryotes.5 billion years ago. In more detail, mitochondria appear to be related to Rickettsiales proteobacteria, in 1918 the French scientist Paul Portier published Les Symbiotes in which he claimed that the mitochondria originated from a symbiosis process. Ivan Wallin extended the idea of an origin to mitochondria in the 1920s. The Russian botanist Boris Kozo-Polyansky was the first to explain the theory in terms of Darwinian evolution, in his 1924 book Symbiogenesis, A New Principle of Evolution he wrote, The theory of symbiogenesis is a theory of selection relying on the phenomenon of symbiosis. These theories were dismissed or ignored. The theory was advanced and substantiated with evidence by Lynn Margulis in a 1967 paper. This last idea has not received much acceptance, because flagella lack DNA, according to Margulis and Dorion Sagan, Life did not take over the globe by combat, but by networking. The possibility that peroxisomes may have an endosymbiotic origin has also been considered, christian de Duve proposed that they may have been the first endosymbionts, allowing cells to withstand growing amounts of free molecular oxygen in the Earths atmosphere. However, it now appears that they may be formed de novo, the endosymbiotic theory is considered to be a type of saltational evolution. According to Keeling and Archibald, the way to distinguish organelles from endosymbionts is by their reduced genome sizes. As an endosymbiont evolves into an organelle, most of their genes are transferred to the host cell genome, the host cell and organelle need to develop a transport mechanism that enables transfer back of the protein products needed by the organelle but now manufactured by the cell. Cyanobacteria and α-proteobacteria are the most closely related free-living organisms to plastids, both cyanobacteria and α-proteobacteria maintain a large genome encoding thousands of proteins. Plastids and mitochondria exhibit a reduction in genome size when compared to their bacterial relatives. Nowack and her colleagues performed gene sequencing on the chromatophore and found that only 867 proteins were encoded by these photosynthetic cells, comparisons with their closest free living cyanobacteria of the genus Synechococcus revealed that chromatophores underwent a drastic genome shrinkage. Thus, these chromatophores were found to be non-functional for organelle-specific purposes when compared to mitochondria and this distinction could have promoted the early evolution of photosynthetic organelles. The loss of autonomy, that is, the loss of many genes from endosymbionts. Taking into account the entire original endosymbiont genome, there are three possible fates for genes over evolutionary time. The loss of autonomy and integration of the endosymbiont with its host can be attributed to nuclear gene transfer
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Spirochaete
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A spirochaete or spirochete is a member of the phylum Spirochaetes, which contains distinctive diderm bacteria, most of which have long, helically coiled cells. Spirochaetes stain gram-negative and are chemoheterotrophic in nature, with lengths between 3 and 500 µm and diameters around 0.09 to at least 3 µm and these cause a twisting motion which allows the spirochaete to move about. When reproducing, a spirochaete will undergo asexual transverse binary fission, most spirochaetes are free-living and anaerobic, but there are numerous exceptions. Spirochaetes bacteria are diverse in their capacity, the ecological niches that they inhabit, as well as molecular characteristics including GC content. Many organisms within the Spirochaetes phylum are causative agents of prevalent diseases, Brachyspira pilosicoli and Brachyspira aalborgi, which cause intestinal spirochaetosis Spirochetes may also cause dementia and may be involved in the pathogenesis of Alzheimers disease. Salvarsan, the first partially organic synthetic antimicrobial drug in history, was effective against spirochaetes only and was primarily used to cure syphilis. The class currently consists of 14 validly named genera across 4 orders and 5 families, the orders Brachyspirales, Brevinematales and Leptospirales each contain a single family, Brachyspiraceae, Brevinemataceae and Leptospiraceae, respectively. The Spirochaetales order harbours two families, Spirochaetaceae and Borreliaceae, additional CSIs have been found exclusively shared by each family within the Spirochaetales. These molecular markers are in agreement with the phylogenetic tree branching of two monophyletic clades within the Spirochaetales order. A conserved signature indel has also found exclusively shared by all Spirochaetes species. This CSI is a 3 amino acid insert in the basal body rod protein FlgC which is an important part of the unique endoflagellar structure shared by Spirochaetes species. Given that the CSI is exclusively shared by members within this phylum, historically, the all families belonging to the Spirochaetes phylum were assigned to a single order, the Spirochaetales. These synapomorphic characteristics justify the phylogenetic divisions and are a means to identify each order/family within the phylum, the phylogeny is based on 16S rRNA-based LTP release 123 by The All-Species Living Tree Project. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature, phylum Spirochaetes Garrity & Holt 2001 Class Spirochaetae Cavalier-Smith 2002 Order Leptospirales Gupta et al.2014 Family Leptospiraceae Hovind-Hougen 1979 emend. Levett et al.2005 Genus Leptonema Hovind-Hougen 1983 Genus Leptospira Noguchi 1917 emend, faine and Stallman 1982 Genus Turneriella Levett et al.2005 Order Brachyspirales corrig. Gupta et al.2013 Genus Exilispira Imachi et al.2008 Family Borreliaceae Gupta et al.2014 Genus Borreliella Adeolu & Gupta 2015 Genus Borrelia Swellengrebel 1907 emend. Pikuta et al.2009 Genus Treponema Schaudinn 1905 emend Abt et al.2013 Notes, ♦ Type strain lost or not available ♪ Prokaryotes where no pure cultures are isolated or available, i
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Flagellum
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A flagellum is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The word flagellum in Latin means whip, the primary role of the flagellum is locomotion, but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. Flagella are organelles defined by function rather than structure, large differences occur between different types of flagella, the prokaryotic and eukaryotic flagella differ greatly in protein composition, structure, and mechanism of propulsion. However, both can be used for swimming, an example of a flagellated bacterium is the ulcer-causing Helicobacter pylori, which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium. An example of a eukaryotic cell is the mammalian sperm cell. Eukaryotic flagella are structurally identical to eukaryotic cilia, although distinctions are made according to function and/or length. Fimbriae and pili are also thin appendages, but have different functions and are usually smaller, three types of flagella have so far been distinguished, bacterial, archaeal, and eukaryotic. The main differences among these three types are, Bacterial flagella are helical filaments, each with a motor at its base which can turn clockwise or counterclockwise. They provide two of several kinds of bacterial motility, archaeal flagella are superficially similar to bacterial flagella, but are different in many details and considered non-homologous. Eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back, eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility. Primary cilia are immotile, and are not undulipodia, they have a structurally different 9+0 axoneme rather than the 9+2 axoneme found in both flagella and motile cilia undulipodia, the bacterial flagellum is made up of the protein flagellin. Its shape is a 20-nanometer-thick hollow tube and it is helical and has a sharp bend just outside the outer membrane, this hook allows the axis of the helix to point directly away from the cell. A shaft runs between the hook and the body, passing through protein rings in the cells membrane that act as bearings. Gram-positive organisms have two of these basal body rings, one in the layer and one in the plasma membrane. The filament ends with a capping protein, the flagellar filament is the long, helical screw that propels the bacterium when rotated by the motor, through the hook. Each protofilament is a series of protein chains. However, Campylobacter jejuni has seven protofilaments, the basal body has several traits in common with some types of secretory pores, such as the hollow, rod-like plug in their centers extending out through the plasma membrane. The bacterial flagellum is driven by an engine made up of protein
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Cilium
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A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the larger cell body. There are two types of cilia, motile cilia and nonmotile, or primary cilia, which serve as sensory organelles. In eukaryotes, motile cilia and flagella together make up a group of known as undulipodia. Eukaryotic cilia are structurally identical to eukaryotic flagella, although distinctions are made according to function and/or length. Biologists have various ideas about how the various flagella may have evolved, cilia can be divided into primary and motile forms. In animals, primary cilia are found on nearly every cell, in comparison to motile cilia, non-motile cilia usually occur one per cell, nearly all mammalian cells have a single non-motile primary cilium. The dendritic knob of the neuron, where the odorant receptors are located. Although the primary cilium was discovered in 1898, it was ignored for a century. Only recently has great progress made in understanding the function of the primary cilium. Until the 1990s, the view of the primary cilium was that it was merely a vestigial organelle without important function. The primary cilium is now known to play an important role in the function of human organs. Larger eukaryotes, such as mammals, have motile cilia as well, motile cilia are usually present on a cells surface in large numbers and beat in coordinated waves. In humans, for example, motile cilia are found in the lining of the trachea, in female mammals, the beating of cilia in the Fallopian tubes moves the ovum from the ovary to the uterus. The functioning of cilia is strongly dependent on the maintenance of optimal levels of fluid bathing the cilia. Epithelial sodium channels ENaC that are expressed along the entire length of cilia apparently serve as sensors that regulate fluid level surrounding the cilia. Ciliates are microscopic organisms that possess motile cilia exclusively and use them for either locomotion or to move liquid over their surface. Inside cilia and flagella is a microtubule-based cytoskeleton called the axoneme, the axoneme of primary cilia typically has a ring of nine outer microtubule doublets, and the axoneme of a motile cilium has two central microtubule singlets in addition to the nine outer doublets
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Evolution of flagella
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There are two competing groups of models for the evolutionary origin of the eukaryotic flagellum. Recent studies on the organizing center suggest that the most recent ancestor of all eukaryotes already had a complex flagellar apparatus. These models argue that cilia developed from pre-existing components of the eukaryotic cytoskeleton as an extension of the spindle apparatus. Long-standing suspicions that tubulin was homologous to FtsZ were confirmed in 1998 by the independent resolution of the 3-dimensional structures of the two proteins and these models argue that the cilium evolved from a symbiotic spirochete that attached to a primitive eukaryote or archaebacterium. The modern version of the hypothesis was first proposed by Lynn Margulis, the hypothesis, though very well publicized, was never widely accepted by the experts, in contrast to Margulis arguments for the symbiotic origin of mitochondria and chloroplasts. Margulis did strongly promote and publish versions of this hypothesis until the end of her life, the primary point in favor of the symbiotic hypothesis is that there are eukaryotes that use symbiotic spirochetes as their motility organelles. An approach to the origin of the bacterial flagellum is suggested by the fact that a subset of flagellar components is similar to the Type III secretory. All currently known nonflagellar Type III transport systems serve the function of injecting toxin into eukaryotic cells and it is hypothesised that the flagellum evolved from the type three secretory system. As such, the type three secretory system supports the hypothesis that the flagellum evolved from a simpler bacterial secretion system, Eubacterial flagellum is a multifunctional organelle, and it is one of the two fundamental subdivisions of prokaryotes. It’s also one of a range of motility systems in bacteria, the structure of the organelle appears like a motor, shaft and a propeller. However, the structure of eubacteria varies based on whether their motor systems run on protons or sodium, the evolutionary process of Eubacterial flagellum is probably an example of indirect evolution. A hypothesis on the pathway of eubacterial flagellum argues that a secretory system evolved first, based around the SMC rod-. This is presumed to be the ancestor of the type-III secretory system. Then, an ion pump was introduced to this structure which improved secretion, the ion pump later became the motor protein. This was followed by the emergence of the filament as part of the protein-secretion structure. Gliding-twitching motility arose at this stage or later and was refined into swimming motility. The recently elucidated archaeal flagellum is analogous, not homologous, to the bacterial one, sequence comparison indicates that the archaeal flagellum is homologous to Type IV pili. Interestingly, some Type IV pili can retract, pilus retraction provides the driving force for a different form of bacterial motility called twitching or social gliding which allows bacterial cells to crawl along a surface
29.
Prokaryotic cytoskeleton
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The prokaryotic cytoskeleton is the collective name for all structural filaments in prokaryotes. Not only have analogues for all major proteins in eukaryotes been found in prokaryotes. Cytoskeletal elements play essential roles in cell division, protection, shape determination, FtsZ acts as an organizer protein and is required for cell division. It is the first component of the septum during cytokinesis, despite this functional similarity to actin, FtsZ is homologous to eukaryal tubulin. Although comparison of the structures of FtsZ and tubulin reveal a weak relationship. Furthermore, like tubulin, monomeric FtsZ is bound to GTP, since FtsZ is essential for cell division in bacteria, this protein is a target for the design of new antibiotics. There currently exist several models and mechanisms that regulate Z-ring formation. One of the model of Z-ring formation was proposed by Rashid, Aijaz and Sing, critical Concentration Gradient Model of Bacterial Cell Division. Available from Nature Precedings <http, //hdl. handle. net/10101/npre.2010.4659. 1>. According to this positive and negative regulators of FtsZ assembly form a gradient inside the bacterial cell. The gradient is such that concentration of FtsZ required for FtsZ assembly is minimum at medial position of cell, hence Z-ring. MreB is a protein believed to be analogous to eukaryal actin. MreB and actin have a primary structure match, but are very similar in terms of 3-D structure. Almost all non-spherical bacteria rely on MreB to determine their shape, MreB assembles into a helical network of filamentous structures just under the cytoplasmic membrane, covering the whole length of the cell. MreB is also important for polarity determination in polar bacteria, as it is responsible for the positioning of at least four different polar proteins in C. crescentus. Crescentin is an analogue of eukaryotic intermediate filaments, furthermore, crescentin filaments are roughly 10 nm in diameter and thus fall within diameter range for eukaryal IFs. Crescentin forms a filament from pole to pole alongside the inner. Both MreB and crescentin are necessary for C. crescentus to exist in its shape, it is believed that MreB molds the cell into a rod shape. ParM is an element that possesses a similar structure to actin. Further, it polymerizes bidirectionally and it exhibits dynamic instability, which are both characteristic of tubulin polymerization
30.
Peroxisome
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Peroxisomes IPA, are organelles found in virtually all eukaryotic cells. e. Ether phospholipids critical for the function of mammalian brains and lungs. They also contain approximately 10% of the activity of two enzymes in the pentose phosphate pathway, which is important for energy metabolism. It is vigorously debated if peroxisomes are involved in isoprenoid and cholesterol synthesis in animals, peroxisomes were identified as organelles by the Belgian cytologist Christian de Duve in 1967 after they had been first described by a Swedish doctoral student, J. Rhodin in 1954. A major function of the peroxisome is the breakdown of very long fatty acids through beta-oxidation. In animal cells, the fatty acids are converted to medium chain fatty acids. In yeast and plant cells, this process is carried out exclusively in peroxisomes, the first reactions in the formation of plasmalogen in animal cells also occur in peroxisomes. Plasmalogen is the most abundant phospholipid in myelin, deficiency of plasmalogens causes profound abnormalities in the myelination of nerve cells, which is one reason why many peroxisomal disorders affect the nervous system. Peroxisomes contain oxidative enzymes, such as D-amino acid oxidase and uric acid oxidase, however the last enzyme is absent in humans, explaining the disease known as gout, caused by the accumulation of uric acid. This reaction is important in liver and kidney cells, where the peroxisomes detoxify various toxic substances that enter the blood, about 25% of the ethanol alcohol humans drink is oxidized to acetaldehyde in this way. Dismutase, the components of the cycle, and the NADP-dehydrogenases of the pentose-phosphate pathway. It has been demonstrated that peroxisomes generate superoxide and nitric oxide radicals, the peroxisome of plant cells is polarised when fighting fungal penetration. Infection causes a molecule to play an antifungal role to be made. Peroxisomes can be derived from the reticulum and replicate by fission. Peroxisome matrix proteins are translated in the prior to import. Specific amino acid sequences at the C-terminus or N-terminus of peroxisomal matrix proteins signals them to be imported into the organelle, there are at least 32 known peroxisomal proteins, called peroxins, which participate in the process of peroxisome assembly. Proteins do not have to unfold to be imported into the peroxisome, the protein receptors, the peroxins PEX5 and PEX7, accompany their cargoes all the way into the peroxisome where they release the cargo and then return to the cytosol – a step named recycling. A model describing the import cycle is referred to as the extended shuttle mechanism, there is now evidence that ATP hydrolysis is required for the recycling of receptors to the cytosol
31.
Christian de Duve
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Christian René Marie Joseph, Viscount de Duve was a Nobel Prize-winning Belgian cytologist and biochemist. He made serendipitous discoveries of two organelles, peroxisome and lysosome, for which he shared the Nobel Prize in Physiology or Medicine in 1974 with Albert Claude. In addition to peroxisome and lysosome, he invented the names such as autophagy, endocytosis. A son of Belgian refugees during the First World War, de Duve was born in Thames Ditton, Surrey and his family returned to Belgium in 1920. He was educated by the Jesuits at Onze-Lieve-Vrouwinstituut in Antwerp, upon earning his MD in 1941, he joined research in chemistry, working on insulin and its role in diabetes mellitus. His thesis earned him the highest university degree agrégation de lenseignement supérieur in 1945, with his work on the purification of penicillin, he obtained an MSc degree in 1946. He went for training under Hugo Theorell at the Karolinska Institutet in Stockholm. He joined the faculty of medicine at Leuven in 1947, in 1960 he was invited to the Rockfeller Institute. With mutual arrangement with Leuven, he became professor in both universities from 1962, dividing his time between Leuven and New York and he became emeritus professor of Leuven university in 1985, and of Rockefeller in 1988. De Duve was granted the rank of Viscount in 1989 by King Baudouin of Belgium and he was also a recipient of Francqui Prize, Gairdner Foundation International Award, Heineken Prize, and E. B. Wilson Medal. In 1974 he founded the International Institute of Cellular and Molecular Pathology in Brussels and he was the founding President of the LOréal-UNESCO Awards for Women in Science. He died on 4 May 2013 by self-induced euthanasia in the presence of all of his children, De Duve was born of a shopkeeper Alphonse de Duve and wife Madeleine Pungs in the village of Thames Ditton, near London. His parents fled Belgium at the outbreak of the First World War, after the war in 1920, at age three, he and his family returned to Belgium. He was a boy, always the best student in school. He was educated by the Jesuits at Onze-Lieve-Vrouwinstituut in Antwerp, before studying at the Catholic University of Leuven in 1934 and he wanted to specialize in endocrinology and joined the laboratory of the Belgian physiologist Joseph P. Bouckaert. During his last year at school in 1940, the Germans invaded Belgium. He was drafted to the Belgian army, and posted in southern France as medical officer, there, he was almost immediately taken as prisoner of war by Germans. Thanks to his ability to speak fluent German and Flemish, he outwitted his captors and he immediately continued his medical course, and obtained his MD in 1941 from Leuven
32.
Genome size
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Genome size is the total amount of DNA contained within one copy of a single genome. It is typically measured in terms of mass in picograms or less frequently in Daltons or as the number of nucleotide base pairs typically in megabases. In diploid organisms, genome size is used interchangeably with the term C-value, an organisms complexity is not directly proportional to its genome size, some single cell organisms have much more DNA than humans. The term genome size is often attributed to Hinegardner, even in discussions dealing specifically with terminology in this area of research. Notably, Hinegardner used the only once, in the title. The term actually seems to have first appeared in 1968 when Hinegardner wondered, in the last paragraph of his article, whether cellular DNA content does, in this context, genome size was being used in the sense of genotype to mean the number of genes. The genome sizes of thousands of eukaryotes have been analyzed over the past 50 years, and these data are available in databases for animals, plants. Nuclear genome size is measured in eukaryotes using either densitometric measurements of Feulgen-stained nuclei or flow cytometry. In prokaryotes, pulsed field gel electrophoresis and complete genome sequencing are the predominant methods of genome size determination, nuclear genome sizes are well known to vary enormously among eukaryotic species. In animals they range more than 3, 300-fold, and in plants they differ by a factor of about 1,000. Protist genomes have been reported to vary more than 300, 000-fold in size, however, although there is no longer any paradoxical aspect to the discrepancy between genome size and gene number, this term remains in common usage. Genome reduction, also known as Genome degradation, is the process by which a genome shrinks relative to its ancestor, genomes fluctuate in size regularly, however, genome size reduction is most significant in bacteria. The most evolutionary significant cases of genome reduction may be the eukaryotic organelles that are derived from bacteria and these organelles are descended from endosymbionts, which can only survive within the host cell and which the host cell likewise needs for survival. Many mitochondria have less than 20 genes in their entire genome, many genes have been transferred to the host nucleus, while others have simply been lost and their function replaced by host processes. Other bacteria have become endosymbionts or obligate intracellular pathogens and experienced extensive genome reduction as a result and this process seems to be dominated by genetic drift resulting from small population size, low recombination rates, and high mutation rates, as opposed to selection for smaller genomes. Some free-living marine bacterioplanktons also shows signs of reduction, which are hypothesized to be driven by natural selection. Obligate endosymbiotic species are characterized by an inability to survive external to their host environment. These species have become a threat to human health, as they are often highly capable of evading human immune systems
33.
Genome
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In modern molecular biology and genetics, a genome is the genetic material of an organism. The genome includes both the genes, the noncoding DNA and the material of the mitochondria and chloroplasts. The term genome was created in 1920 by Hans Winkler, professor of botany at the University of Hamburg, the Oxford Dictionary suggests the name is a blend of the words gene and chromosome. However, see omics for a thorough discussion. A few related -ome words already existed—such as biome, rhizome, Some organisms have multiple copies of chromosomes, diploid, triploid, tetraploid and so on. In classical genetics, in a sexually reproducing organism the gamete has half the number of chromosomes of the somatic cell, the halving of the genetic material in gametes is accomplished by the segregation of homologous chromosomes during meiosis. Additionally, the genome can comprise non-chromosomal genetic elements such as viruses, plasmids, even in species that exist in only one sex, what is described as a genome sequence may be a composite read from the chromosomes of various individuals. Colloquially, the genetic makeup is sometimes used to signify the genome of a particular individual or organism. Both the number of pairs and the number of genes vary widely from one species to another. The only exception in humans is found in red blood cells which become enucleated during development. In 1976, Walter Fiers at the University of Ghent was the first to establish the complete sequence of a viral RNA-genome. The next year Fred Sanger completed the first DNA-genome sequence, Phage Φ-X174, the first genome sequence for an archaeon, Methanococcus jannaschii, was completed in 1996, again by The Institute for Genomic Research. The development of new technologies has made it easier and cheaper to do sequencing. The US National Institutes of Health maintains one of several databases of genomic information. Among the thousands of completed genome sequencing projects include those for rice, a mouse, the plant Arabidopsis thaliana, the fish. In December 2013, scientists first sequenced the genome of a Neanderthal. The genome was extracted from the toe bone of a 130, new sequencing technologies, such as massive parallel sequencing have also opened up the prospect of personal genome sequencing as a diagnostic tool, as pioneered by Manteia Predictive Medicine. A major step toward that goal was the completion in 2007 of the genome of James D. Watson
34.
Protein
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Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide, short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance. Most proteins consist of linear polymers built from series of up to 20 different L-α-amino acids, all proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen. The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar
35.
Alphaproteobacteria
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Alphaproteobacteria is a class of bacteria in the phylum Proteobacteria. Its members are diverse and possess few commonalities, but nevertheless share a common ancestor. Like all Proteobacteria, its members are Gram-negative and some of its intracellular parasitic members lack peptidoglycan and are consequently gram variable. Moreover, the class includes the protomitochondrion, the bacterium that was engulfed by the ancestor and gave rise to the mitochondria. A species of technological interest is Rhizobium radiobacter, scientists use this species to transfer foreign DNA into plant genomes. There is some disagreement on the phylogeny of the orders, especially for the location of the Pelagibacterales and this issue stems form the large difference in gene content and the large difference in GC-richness between members of several order. Specifically, Pelagibacterales, Rickettsiales and Holosporales contains species with AT-rich genomes and it has been argued that it could be a case of convergent evolution that would result in an artefactual clustering. The basal group is Magnetococcidae, which is composed by a diversity of magnetotactic bacteria. The Rickettsidae is composed of the intracellular Rickettsiales and the free-living Pelagibacterales, the Caulobacteridae is composed of the Holosporales, Rhodospirillales, Sphingomonadales, Rhodobacterales, Caulobacterales, Kiloniellales, Kordiimonadales, Parvularculales and Sneathiellales. These molecular signatures provide novel means for the circumscription of these taxonomic groups, alphaproteobacteria at the US National Library of Medicine Medical Subject Headings Bacterial Phylogeny Webpage, Alpha Proteobacteria
36.
Chromatophore
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Chromatophores are pigment-containing and light-reflecting cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, have a class of cells called melanocytes for coloration, Chromatophores are largely responsible for generating skin and eye colour in ectothermic animals and are generated in the neural crest during embryonic development. Mature chromatophores are grouped into subclasses based on their colour under white light, xanthophores, erythrophores, iridophores, leucophores, melanophores, some species can rapidly change colour through mechanisms that translocate pigment and reorient reflective plates within chromatophores. This process, often used as a type of camouflage, is called physiological colour change or metachrosis, cephalopods such as the octopus have complex chromatophore organs controlled by muscles to achieve this, whereas vertebrates such as chameleons generate a similar effect by cell signalling. Such signals can be hormones or neurotransmitters and may be initiated by changes in mood, temperature, Chromatophores are studied by scientists to understand human disease and as a tool in drug discovery. Aristotle mentioned the ability of the octopus to change colour for camouflage and signalling in his Historia animalium, The octopus. Seeks its prey by so changing its colour as to render it like the colour of the adjacent to it, it does so also when alarmed. Giosuè Sangiovanni was the first to describe invertebrate pigment-bearing cells as cromoforo in an Italian science journal in 1819 and these changes were effected in such a manner that clouds, varying in tint between a hyacinth red and a chestnut-brown, were continually passing over the body. Any part, being subjected to a shock of galvanism, became almost black, a similar effect. These clouds, or blushes as they may be called, are said to be produced by the expansion and contraction of minute vesicles containing variously coloured fluids. The term chromatophore was adopted as the name for pigment-bearing cells derived from the neural crest of cold-blooded vertebrates, the word itself comes from the Greek words khrōma meaning colour, and phoros meaning bearing. In contrast, the word chromatocyte was adopted for the responsible for colour found in birds. Only one such type, the melanocyte, has been identified in these animals. It was only in the 1960s that chromatophores were well understood to enable them to be classified based on their appearance. This classification system persists to this day, even though the biochemistry of the pigments may be useful to a scientific understanding of how the cells function. Colour-producing molecules fall into two classes, biochromes and structural colours or schemochromes. The biochromes include true pigments, such as carotenoids and pteridines and these pigments selectively absorb parts of the visible light spectrum that makes up white light while permitting other wavelengths to reach the eye of the observer. Structural colours are produced by combinations of diffraction, reflection or scattering of light from structures with a scale around a quarter of the wavelength of light
37.
Cell division
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Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a cell cycle. Meiosis results in four daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division, both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor, prokaryotes undergo a vegetative cell division known as binary fission, where their genetic material is segregated equally into two daughter cells. All cell divisions, regardless of organism, are preceded by a round of DNA replication. For simple unicellular organisms such as the amoeba, one cell division is equivalent to reproduction – an entire new organism is created, on a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Mitotic cell division enables sexually reproducing organisms to develop from the one-celled zygote, after growth, cell division by mitosis allows for continual construction and repair of the organism. The human body experiences about 10 quadrillion cell divisions in a lifetime, the primary concern of cell division is the maintenance of the original cells genome. Before division can occur, the information that is stored in chromosomes must be replicated. A great deal of infrastructure is involved in keeping genomic information consistent between generations. Interphase is the process a cell must go through mitosis, meiosis. Interphase consists of four stages, G1, S, G2. If the cell does not progress through G1, the cell enters a stage called G0. In G0, cells are living but they are put on hold. The cells may later be called back into interphase if needed at a later time, there are checkpoints during interphase that allow the cell to be either progressed or denied further development. In S phase, the chromosomes are replicated in order for the content to be maintained. During G2, the cell undergoes the final stages of growth before it enters the M phase, the M phase, can be either mitosis or meiosis depending on the type of cell
38.
Synechococcus
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Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 to 1.5 µm, the photosynthetic coccoid cells are preferentially found in well–lit surface waters where it can be very abundant. Many freshwater species of Synechococcus have also been described, the genome of S. elongatus strain PCC7002 has a size of 3008047 bp, whereas the oceanic strain WH8102 has a genome of size 2.4 Mbp. Synechococcus is one of the most important components of the prokaryotic autotrophic picoplankton in the temperate to tropical oceans and this definition of the genus Synechococcus contained organisms of considerable genetic diversity and was later subdivided into subgroups based on the presence of the accessory pigment phycoerythrin. The marine forms of Synechococcus are coccoid cells between 0.6 and 1.6 µm in size and they are Gram-negative cells with highly structured cell walls that may contain projections on their surface. Electron microscopy frequently reveals the presence of phosphate inclusions, glycogen granules, cells are known to be motile by a gliding method and a novel uncharacterized, nonphototactic swimming method that does not involve flagellar motion. Marine Synechococcus species are not thought to fix nitrogen. The main photosynthetic pigment in Synechococcus is chlorophyll a, while its major accessory pigments are phycobilliproteins, the four commonly recognized phycobilins are phycocyanin, allophycocyanin, allophycocyanin B and phycoerythrin. In addition Synechococcus also contains zeaxanthin but no diagnostic pigment for this organism is known, zeaxanthin is also found in Prochlorococcus, red algae and as a minor pigment in some chlorophytes and eustigmatophytes. Similarly, phycoerythrin is also found in rhodophytes and some cryptomonads, phylogenetic description of Synechococcus is difficult. Isolates are morphologically similar, yet exhibit a G+C content ranging from 39 to 71%. Initially, attempts were made to divide the group into three subclusters, each with a range of genomic G+C content. The observation that open-ocean isolates alone nearly span the complete G+C spectrum, however, bergeys Manual now divides Synechococcus into five clusters based on morphology, physiology, and genetic traits. Cluster 1 includes relatively large nonmotile obligate photoautotrophs that exhibit low salt tolerance, reference strains for this cluster are PCC6301 and PCC6312, which were isolated from fresh water in Texas and California, respectively. Cluster 2 also is characterized by low salt tolerance, cells are obligate photoautrotrophs, lack phycoerythrin, and are thermophilic. The reference strain PCC6715 was isolated from a hot spring in Yellowstone National Park, cluster 3 includes phycoerythrin-lacking marine Synechococcus species that are euryhaline, i. e. capable of growth in both marine and freshwater environments. Several strains, including the reference strain PCC7003, are facultative heterotrophs, cluster 4 contains a single isolate, PCC7335. This strain contains phycoerthrin and was first isolated from the zone in Puerto Peñasco, Mexico
39.
Photosynthesis
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Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms activities. In most cases, oxygen is released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis, such organisms are called photoautotrophs, in plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, in the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate. Using the ATP and NADPH produced by the light-dependent reactions, the compounds are then reduced and removed to form further carbohydrates. Cyanobacteria appeared later, the oxygen they produced contributed directly to the oxygenation of the Earth. Today, the rate of energy capture by photosynthesis globally is approximately 130 terawatts. Photosynthetic organisms also convert around 100–115 thousand million tonnes of carbon into biomass per year. Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from carbon dioxide, however, not all organisms that use light as a source of energy carry out photosynthesis, photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon. In plants, algae, and cyanobacteria, photosynthesis releases oxygen and this is called oxygenic photosynthesis and is by far the most common type of photosynthesis used by living organisms. Although there are differences between oxygenic photosynthesis in plants, algae, and cyanobacteria, the overall process is quite similar in these organisms. There are also varieties of anoxygenic photosynthesis, used mostly by certain types of bacteria. Carbon dioxide is converted into sugars in a process called carbon fixation, photosynthesis provides the energy in the form of free electrons that are used to split carbon from carbon dioxide that is then used to fix that carbon once again as carbohydrate. Carbon fixation is a redox reaction, so photosynthesis supplies the energy that drives both process. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the energy-storage molecules ATP, during the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide. Most organisms that utilize oxygenic photosynthesis use visible light for the light-dependent reactions, some organisms employ even more radical variants of photosynthesis. Some archea use a method that employs a pigment similar to those used for vision in animals. The bacteriorhodopsin changes its configuration in response to sunlight, acting as a proton pump and this produces a proton gradient more directly, which is then converted to chemical energy
40.
Evolution
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Evolution is change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of organisation, including the levels of species, individual organisms. In July 2016, scientists reported identifying a set of 355 genes from the LUCA of all living on Earth. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, existing patterns of biodiversity have been shaped both by speciation and by extinction. More than 99 percent of all species that lived on Earth are estimated to be extinct. Estimates of Earths current species range from 10 to 14 million, more recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. In the mid-19th century, Charles Darwin formulated the theory of evolution by natural selection. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are fitted for the functional roles they perform. The processes by which the changes occur, from one generation to another, are called evolutionary processes or mechanisms, the four most widely recognized evolutionary processes are natural selection, genetic drift, mutation and gene migration. Natural selection and genetic drift sort variation, mutation and gene migration create variation, consequences of selection can include meiotic drive, nonrandom mating and genetic hitchhiking. In the early 20th century the modern evolutionary synthesis integrated classical genetics with Darwins theory of evolution by natural selection through the discipline of population genetics, the importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis, evolutionism, evolutionary computation, a sub-field of artificial intelligence, involves the application of Darwinian principles to problems in computer science. The proposal that one type of organism could descend from another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander, such proposals survived into Roman times. The poet and philosopher Lucretius followed Empedocles in his masterwork De rerum natura, in contrast to these materialistic views, Aristotelianism considered all natural things as actualisations of fixed natural possibilities, known as forms. This was part of a teleological understanding of nature in which all things have an intended role to play in a divine cosmic order. In the 17th century, the new method of modern science rejected the Aristotelian approach, however, this new approach was slow to take root in the biological sciences, the last bastion of the concept of fixed natural types. The biological classification introduced by Carl Linnaeus in 1735 explicitly recognized the nature of species relationships. Other naturalists of this time speculated on the change of species over time according to natural laws
41.
Horizontal gene transfer
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Horizontal gene transfer or lateral gene transfer is the movement of genetic material between unicellular and/or multicellular organisms other than by the transmission of DNA from parent to offspring. HGT is an important factor in the evolution of many organisms and it often involves temperate bacteriophages and plasmids. Most thinking in genetics has focused upon vertical transfer, but horizontal gene transfer is important, artificial horizontal gene transfer is a form of genetic engineering. Inter-bacterial gene transfer was first described in Japan in a 1959 publication that demonstrated the transfer of resistance between different species of bacteria. In the mid-1980s, Syvanen predicted that lateral gene transfer existed, had biological significance, as Jian, Rivera and Lake put it, Increasingly, studies of genes and genomes are indicating that considerable horizontal transfer has occurred between prokaryotes. The phenomenon appears to have had significance for unicellular eukaryotes as well. As Bapteste et al. observe, additional evidence suggests that gene transfer might also be an important evolutionary mechanism in protist evolution, there is some evidence that even higher plants and animals have been affected and this has raised concerns for safety. Grafting of one plant to another can transfer chloroplasts, mitochondrial DNA, some Lepidoptera have been genetically modified by horizontal gene transfer from the wasp bracovirus. Bites from the insect Reduviidae can, via a parasite, infect humans with the trypanosomal Chagas disease and it has been suggested that lateral gene transfer to humans from bacteria may play a role in cancer. Richardson and Palmer state, Horizontal gene transfer has played a role in bacterial evolution and is fairly common in certain unicellular eukaryotes. However, the prevalence and importance of HGT in the evolution of multicellular eukaryotes remain unclear, some have argued that the process may be a hidden hazard of genetic engineering as it could allow transgenic DNA to spread from species to species. There are several mechanisms for horizontal gene transfer, Transformation, the alteration of a cell resulting from the introduction, uptake. This process is common in bacteria, but less so in eukaryotes. Transformation is often used in laboratories to insert genes into bacteria for experiments or for industrial or medical applications. See also molecular biology and biotechnology, transduction, the process in which bacterial DNA is moved from one bacterium to another by a virus. Bacterial conjugation, a process involves the transfer of DNA via a plasmid from a donor cell to a recombinant recipient cell during cell-to-cell contact. Gene transfer agents, virus-like elements encoded by the host that are found in the alphaproteobacteria order Rhodobacterales. A transposon is a segment of DNA that can sometimes pick up a resistance gene and insert it into a plasmid or chromosome
42.
Complementary DNA
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In genetics, complementary DNA is double-stranded DNA synthesized from a single stranded RNA template in a reaction catalyzed by the enzyme reverse transcriptase. CDNA is often used to clone genes in prokaryotes. When scientists want to express a protein in a cell that does not normally express that protein. CDNA is also produced naturally by retroviruses and then integrated into the hosts genome, the term cDNA is also used, typically in a bioinformatics context, to refer to an mRNA transcripts sequence, expressed as DNA bases rather than RNA bases. The number of introns present in a cDNA is zero, since it is derived from eukaryotic mRNA which does not contain introns, although there are several methods for doing so, cDNA is most often synthesized from mature mRNA using the enzyme reverse transcriptase. This enzyme, which occurs in retroviruses, operates on a single strand of mRNA. To obtain eukaryotic cDNA whose introns have been removed, A eukaryotic cell transcribes the DNA into RNA, the same cell processes the pre-mRNA strands by removing introns, and adding a poly-A tail and 5’ Methyl-Guanine cap This mixture of mature mRNA strands is extracted from the cell. The Poly-A tail of the post-transcription mRNA can be taken advantage of with oligo beads in an affinity chromatography assay and this synthesizes one complementary strand of DNA hybridized to the original mRNA strand. To synthesize an additional DNA strand, traditionally one would digest the RNA of the strand, using an enzyme like RNase H. After digestion of the RNA, a single stranded DNA is left and because single stranded nucleic acids are hydrophobic and it is likely that the ssDNA forms a hairpin loop at the 3 end. From the hairpin loop, a DNA polymerase can use it as a primer to transcribe a complementary sequence for the ss cDNA. Now, you should be left with a double stranded cDNA with identical sequence as the mRNA of interest, Complementary DNA is often used in gene cloning or as gene probes or in the creation of a cDNA library. Partial sequences of cDNAs are often obtained as expressed sequence tags and this is achieved by designing sequence-specific DNA primers that hybridize to the 5 and 3 ends of a cDNA region coding for a protein. Once amplified, the sequence can be cut at each end with nucleases, such vectors allow for self-replication, inside the cells, and potentially integration in the host DNA. They typically also contain a promoter to drive transcription of the target cDNA into mRNA. Some viruses also use cDNA to turn their viral RNA into mRNA, the mRNA is used to make viral proteins to take over the host cell. CDNA library cDNA microarray RNA-Seq H-Invitational Database Functional Annotation of the Mouse database Complementary DNA tool
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Messenger RNA
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Messenger RNA is a large family of RNA molecules that convey genetic information from DNA to the ribosome, where they specify the amino acid sequence of the protein products of gene expression. As in DNA, mRNA genetic information is in the sequence of nucleotides, each codon encodes for a specific amino acid, except the stop codons, which terminate protein synthesis. It should not be confused with mitochondrial DNA, the brief existence of an mRNA molecule begins with transcription, and ultimately ends in degradation. During its life, a molecule may also be processed, edited. Eukaryotic mRNA molecules often require extensive processing and transport, while prokaryotic mRNA molecules do not, a molecule of eukaryotic mRNA and the proteins surrounding it are together called a messenger RNP. Transcription is when RNA is made from DNA, during transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes, the short-lived, unprocessed or partially processed product is termed precursor mRNA, or pre-mRNA, once completely processed, it is termed mature mRNA. Processing of mRNA differs greatly among eukaryotes, bacteria, and archea, non-eukaryotic mRNA is, in essence, mature upon transcription and requires no processing, except in rare cases. Eukaryotic pre-mRNA, however, requires extensive processing, a 5 cap is a modified guanine nucleotide that has been added to the front or 5 end of a eukaryotic messenger RNA shortly after the start of transcription. The 5 cap consists of a terminal 7-methylguanosine residue that is linked through a 5-5-triphosphate bond to the first transcribed nucleotide and its presence is critical for recognition by the ribosome and protection from RNases. Cap addition is coupled to transcription, and occurs co-transcriptionally, such that each influences the other, shortly after the start of transcription, the 5 end of the mRNA being synthesized is bound by a cap-synthesizing complex associated with RNA polymerase. This enzymatic complex catalyzes the reactions that are required for mRNA capping. Synthesis proceeds as a biochemical reaction. In some instances, an mRNA will be edited, changing the composition of that mRNA. An example in humans is the apolipoprotein B mRNA, which is edited in some tissues, the editing creates an early stop codon, which, upon translation, produces a shorter protein. Polyadenylation is the covalent linkage of a moiety to a messenger RNA molecule. In eukaryotic organisms most messenger RNA molecules are polyadenylated at the 3 end, the poly tail and the protein bound to it aid in protecting mRNA from degradation by exonucleases. Polyadenylation is also important for transcription termination, export of the mRNA from the nucleus, MRNA can also be polyadenylated in prokaryotic organisms, where poly tails act to facilitate, rather than impede, exonucleolytic degradation
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Autophagy
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Autophagy is the natural, regulated, destructive mechanism of the cell that disassembles unnecessary or dysfunctional components. Autophagy allows the orderly degradation and recycling of cellular components, in macroautophagy, targeted cytoplasmic constituents are isolated from the rest of the cell within a double-membraned vesicle known as an autophagosome. The autophagosome eventually fuses with lysosomes and the contents are degraded and recycled, two additional forms of autophagy are also commonly described, microautophagy and chaperone-mediated autophagy. In disease, autophagy has been seen as a response to stress. In the extreme case of starvation, the breakdown of cellular components promotes cellular survival by maintaining cellular energy levels, the name autophagy was coined by Belgian biochemist Christian de Duve in 1963. Autophagy was first observed by Keith R. Porter and his student Thomas Ashford at the Rockefeller Institute and they called this autolysis after Christian de Duve and Alex B. However Porter and Ashford wrongly interpreted their data as lysosome formation, lysosomes could not be cell organelles, but part of cytoplasm such as mitochondria, and that hydrolytic enzymes were produced by microbodies. In 1963 researchers published a detailed description of focal cytoplasmic degradation. Inspired by this discovery, de Duve christened the phenomena autophagy, unlike Porter and Ashford, de Duve conceived the term as a part of lysosomal function while describing the role of glucagon as a major inducer of cell degradation in the liver. With his student Peter, he established that lysosomes are responsible for glucagon-induced autophagy and this was the first time the fact that lysosomes were established as the sites of intracellular autophagy. A new era of research began in 1990s when several groups of scientists independently discovered autophagy-related genes using the budding yeast. They soon found that they were in fact looking at essentially the same pathway, initially, the genes discovered by these and other yeast groups were given different names. A unified nomenclature was advocated in 2003 by the yeast researchers to use ATG to denote autophagy genes, the 2016 Nobel Prize in Physiology or Medicine was awarded to Yoshinori Ohsumi. Dr. Ohsumi’s contribution to research is well recognized. However, some have pointed out that the award could have been more inclusive, the field of autophagy research experienced accelerated growth at the turn of the century. Knowledge of ATG genes provided scientists more convenient tools to dissect functions of autophagy in human health, in 1999, a landmark discovery connecting autophagy with cancer was published by Beth Levine’s group. To this date, relationship between cancer and autophagy continues to be a theme of autophagy research. The roles of autophagy in neurodegeneration and immune defense also received considerable attention, in 2003, the first Gordon conference on autophagy was held at Waterville
. PMID 13741827.
