A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+. The free energy released in this process is used to form the high-energy molecules ATP and NADH. Glycolysis is a sequence of ten enzyme-catalyzed reactions. Most monosaccharides, such as fructose and galactose, can be converted to one of these intermediates; the intermediates may be directly useful. For example, the intermediate dihydroxyacetone phosphate is a source of the glycerol that combines with fatty acids to form fat. Glycolysis is an oxygen-independent metabolic pathway; the wide occurrence of glycolysis indicates. Indeed, the reactions that constitute glycolysis and its parallel pathway, the pentose phosphate pathway, occur metal-catalyzed under the oxygen-free conditions of the Archean oceans in the absence of enzymes. In most organisms, glycolysis occurs in the cytosol; the most common type of glycolysis is the Embden–Meyerhof–Parnas, discovered by Gustav Embden, Otto Meyerhof, Jakub Karol Parnas.
Glycolysis refers to other pathways, such as the Entner–Doudoroff pathway and various heterofermentative and homofermentative pathways. However, the discussion here will be limited to the Embden–Meyerhof–Parnas pathway; the glycolysis pathway can be separated into two phases: The Preparatory/Investment Phase – wherein ATP is consumed. The Pay Off Phase – wherein ATP is produced; the overall reaction of glycolysis is: The use of symbols in this equation makes it appear unbalanced with respect to oxygen atoms, hydrogen atoms, charges. Atom balance is maintained by the two phosphate groups: Each exists in the form of a hydrogen phosphate anion, dissociating to contribute 2 H+ overall Each liberates an oxygen atom when it binds to an ADP molecule, contributing 2 O overallCharges are balanced by the difference between ADP and ATP. In the cellular environment, all three hydroxyl groups of ADP dissociate into −O− and H+, giving ADP3−, this ion tends to exist in an ionic bond with Mg2+, giving ADPMg−.
ATP behaves identically except that it has four hydroxyl groups, giving ATPMg2−. When these differences along with the true charges on the two phosphate groups are considered together, the net charges of −4 on each side are balanced. For simple fermentations, the metabolism of one molecule of glucose to two molecules of pyruvate has a net yield of two molecules of ATP. Most cells will carry out further reactions to'repay' the used NAD+ and produce a final product of ethanol or lactic acid. Many bacteria use inorganic compounds as hydrogen acceptors to regenerate the NAD+. Cells performing aerobic respiration synthesize much more ATP, but not as part of glycolysis; these further aerobic reactions use pyruvate and NADH + H+ from glycolysis. Eukaryotic aerobic respiration produces 34 additional molecules of ATP for each glucose molecule, however most of these are produced by a vastly different mechanism to the substrate-level phosphorylation in glycolysis; the lower-energy production, per glucose, of anaerobic respiration relative to aerobic respiration, results in greater flux through the pathway under hypoxic conditions, unless alternative sources of anaerobically oxidizable substrates, such as fatty acids, are found.
The pathway of glycolysis as it is known today took 100 years to discover. The combined results of many smaller experiments were required in order to understand the pathway as a whole; the first steps in understanding glycolysis began in the nineteenth century with the wine industry. For economic reasons, the French wine industry sought to investigate why wine sometime turned distasteful, instead of fermenting into alcohol. French scientist Louis Pasteur researched this issue during the 1850s, the results of his experiments began the long road to elucidating the pathway of glycolysis, his experiments showed. While Pasteur's experiments were groundbreaking, insight into the component steps of glycolysis were provided by the non-cellular fermentation experiments of Eduard Buchner during the 1890s. Buchner demonstrated that the conversion of glucose to ethanol was possible using a non-living extract of yeast; this experiment not only revolutionized biochemistry, but allowed scientists to analyze this pathway in a more controlled lab setting.
In a series of experiments, scientists Arthur Harden and William Young discovered more pieces of glycolysis. They discovered the regulatory effects of ATP on glucose consumption during alcohol fermentation, they shed light on the role of one compound as a glycolysis intermediate: fructose 1,6-bisphosphate. The elucidation of fructose 1,6-bisphosphate was accomplished by measuring CO2 levels when yeast juice was incubated with glucose. CO2 production increased then slowed down. Harden and Young noted that this process would restart if an inorganic phosphate was added to the mixture. Harden and Young deduced that this process produced organic phosphate esters, further experiments allowed them to extract fructose diphosphate. Arthur Harden and William Young along with Nick Sheppard determined, in a second experiment, that a heat-sensitive high-molecular-weight subcellular fraction and a heat-insensitive low-molecular-weight cytoplasm fraction are required together for fermenta
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
The annelids known as the ringed worms or segmented worms, are a large phylum, with over 22,000 extant species including ragworms and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, yet others in moist terrestrial environments; the annelids are bilaterally symmetrical, coelomate, invertebrate organisms. They have parapodia for locomotion. Most textbooks still use the traditional division into polychaetes and leech-like species. Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora and Sipuncula regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a "super-phylum" of protostomes that includes molluscs, brachiopods and nemerteans; the basic annelid form consists of multiple segments.
Each segment has the same sets of organs and, in most polychates, has a pair of parapodia that many species use for locomotion. Septa separate the segments of many species, but are poorly defined or absent in others, Echiura and Sipuncula show no obvious signs of segmentation. In species with well-developed septa, the blood circulates within blood vessels, the vessels in segments near the front ends of these species are built up with muscles that act as hearts; the septa of such species enable them to change the shapes of individual segments, which facilitates movement by peristalsis or by undulations that improve the effectiveness of the parapodia. In species with incomplete septa or none, the blood circulates through the main body cavity without any kind of pump, there is a wide range of locomotory techniques – some burrowing species turn their pharynges inside out to drag themselves through the sediment. Earthworms are oligochaetes that support terrestrial food chains both as prey and in some regions are important in aeration and enriching of soil.
The burrowing of marine polychaetes, which may constitute up to a third of all species in near-shore environments, encourages the development of ecosystems by enabling water and oxygen to penetrate the sea floor. In addition to improving soil fertility, annelids serve humans as bait. Scientists observe annelids to monitor the quality of fresh water. Although blood-letting is used less by doctors, some leech species are regarded as endangered species because they have been over-harvested for this purpose in the last few centuries. Ragworms' jaws are now being studied by engineers as they offer an exceptional combination of lightness and strength. Since annelids are soft-bodied, their fossils are rare – jaws and the mineralized tubes that some of the species secreted. Although some late Ediacaran fossils may represent annelids, the oldest known fossil, identified with confidence comes from about 518 million years ago in the early Cambrian period. Fossils of most modern mobile polychaete groups appeared by the end of the Carboniferous, about 299 million years ago.
Palaeontologists disagree about whether some body fossils from the mid Ordovician, about 472 to 461 million years ago, are the remains of oligochaetes, the earliest indisputable fossils of the group appear in the Tertiary period, which began 66 million years ago. There are over 22,000 living annelid species, ranging in size from microscopic to the Australian giant Gippsland earthworm and Amynthas mekongianus, which can both grow up to 3 metres long. Although research since 1997 has radically changed scientists' views about the evolutionary family tree of the annelids, most textbooks use the traditional classification into the following sub-groups: Polychaetes; as their name suggests, they have multiple chetae per segment. Polychaetes have parapodia that function as limbs, nuchal organs that are thought to be chemosensors. Most are marine animals, although a few species live in fresh water and fewer on land. Clitellates; these have few or no chetae per segment, no nuchal organs or parapodia. However, they have a unique reproductive organ, the ring-shaped clitellum around their bodies, which produces a cocoon that stores and nourishes fertilized eggs until they hatch or, in moniligastrids, yolky eggs that provide nutrition for the embyros.
The clitellates are sub-divided into: Oligochaetes. Oligochaetes have a sticky pad in the roof of the mouth. Most are burrowers that feed on wholly or decomposed organic materials. Hirudinea, whose name means "leech-shaped" and whose best known members are leeches. Marine species are blood-sucking parasites on fish, while most freshwater species are predators, they have suckers at both ends of their bodies, use these to move rather like inchworms. The Archiannelida, minute annelids that live in the spaces between grains of marine sediment, were treated as a separate class because of their simple body structure, but are now regarded as polychaetes; some other groups of animals have been classified in various ways, but are now regarded as annelids: Pogonophora / Siboglinidae were first discovered in 1914, their lack of a recognizable gut made it difficult to classify them. They have been classified as a separate phylum, Pogonophora, or as two phyla and Vestimentifera. More they have been re-classified as a family, Siboglinidae
A biomolecule or biological molecule is a loosely used term for molecules and ions that are present in organisms, essential to some biological process such as cell division, morphogenesis, or development. Biomolecules include large macromolecules such as proteins, carbohydrates and nucleic acids, as well as small molecules such as primary metabolites, secondary metabolites, natural products. A more general name for this class of material is biological materials. Biomolecules are endogenous but may be exogenous. For example, pharmaceutical drugs may be natural products or semisynthetic or they may be synthetic. Biology and its subsets of biochemistry and molecular biology study biomolecules and their reactions. Most biomolecules are organic compounds, just four elements—oxygen, carbon and nitrogen—make up 96% of the human body's mass, but many other elements, such as the various biometals, are present in small amounts. The uniformity of specific types of molecules and of some metabolic pathways as invariant features between the diversity of life forms is called "biochemical universals" or "theory of material unity of the living beings", a unifying concept in biology, along with cell theory and evolution theory.
A diverse range of biomolecules exist, including: Small molecules: Lipids, fatty acids, sterols, monosaccharides Vitamins Hormones, neurotransmitters Metabolites Monomers and polymers: Nucleosides are molecules formed by attaching a nucleobase to a ribose or deoxyribose ring. Examples of these include cytidine, adenosine and thymidine. Nucleosides can be phosphorylated by specific kinases in producing nucleotides. Both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides. DNA uses the deoxynucleotides C, G, A, T, while RNA uses the ribonucleotides C, G, A, U. Modified bases are common, as found in ribosomal RNA or transfer RNAs or for discriminating the new from old strands of DNA after replication; each nucleotide is made of a pentose and one to three phosphate groups. They contain carbon, oxygen and phosphorus, they serve as sources of chemical energy, participate in cellular signaling, are incorporated into important cofactors of enzymatic reactions.
DNA structure is dominated by the well-known double helix formed by Watson-Crick base-pairing of C with G and A with T. This is known as B-form DNA, is overwhelmingly the most favorable and common state of DNA. DNA can sometimes occur as single strands or as A-form or Z-form helices, in more complex 3D structures such as the crossover at Holliday junctions during DNA replication. RNA, in contrast, forms large and complex 3D tertiary structures reminiscent of proteins, as well as the loose single strands with locally folded regions that constitute messenger RNA molecules; those RNA structures contain many stretches of A-form double helix, connected into definite 3D arrangements by single-stranded loops and junctions. Examples are tRNA, ribosomes and riboswitches; these complex structures are facilitated by the fact that RNA backbone has less local flexibility than DNA but a large set of distinct conformations because of both positive and negative interactions of the extra OH on the ribose. Structured RNA molecules can do specific binding of other molecules and can themselves be recognized specifically.
Monosaccharides are the simplest form of carbohydrates with only one simple sugar. They contain an aldehyde or ketone group in their structure; the presence of an aldehyde group in a monosaccharide is indicated by the prefix aldo-. A ketone group is denoted by the prefix keto-. Examples of monosaccharides are the hexoses, fructose, Tetroses, galactose, pentoses and deoxyribose. Consumed fructose and glucose have different rates of gastric emptying, are differentially absorbed and have different metabolic fates, providing multiple opportunities for 2 different saccharides to differentially affect food intake. Most saccharides provide fuel for cellular respiration. Disaccharides are formed when two monosaccharides, or two single simple sugars, form a bond with removal of water, they can be hydrolyzed to yield their saccharin building blocks by boiling with dilute acid or reacting them with appropriate enzymes. Examples of disaccharides include sucrose and lactose. Polysaccharides are polymerized complex carbohydrates.
They have multiple simple sugars. Examples are starch and glycogen, they are large and have a complex branched connectivity. Because of their size, polysaccharides are not water-soluble, but their many hydroxy groups become hydrated individually when exposed to water, some polysaccharides form thick colloidal dispersions when heated in water. Shorter polysaccharides, with 3 - 10 monomers, are called oligosaccharides. A fluorescent indicato