1.
Cell (biology)
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The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology. Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins. Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells. Most plant and animal cells are only under a microscope. The cell was discovered by Robert Hooke in 1665, who named the unit for its resemblance to cells inhabited by Christian monks in a monastery. Cells emerged on Earth at least 3.5 billion years ago, Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes
2.
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
3.
Chromosome
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A chromosome is a DNA molecule with part or all of the genetic material of an organism. Prokaryotes usually have one single circular chromosome, whereas most eukaryotes are diploid, chromosomes in eukaryotes are composed of chromatin fiber. Chromatin fiber is made of nucleosomes, a nucleosome is a histone octamer with part of a longer DNA strand attached to and wrapped around it. Chromatin fiber, together with associated proteins is known as chromatin, chromatin is present in most cells, with a few exceptions, for example, red blood cells. Occurring only in the nucleus of cells, chromatin contains the vast majority of DNA, except for a small amount inherited maternally. Chromosomes are normally visible under a microscope only when the cell is undergoing the metaphase of cell division. Before this happens every chromosome is copied once, and the copy is joined to the original by a centromere resulting in an X-shaped structure, the original chromosome and the copy are now called sister chromatids. During metaphase, when a chromosome is in its most condensed state, in this highly condensed form chromosomes are easiest to distinguish and study. In prokaryotic cells, chromatin occurs free-floating in cytoplasm, as these cells lack organelles, the main information-carrying macromolecule is a single piece of coiled double-helix DNA, containing many genes, regulatory elements and other noncoding DNA. The DNA-bound macromolecules are proteins that serve to package the DNA, chromosomes vary widely between different organisms. Some species such as certain bacteria also contain plasmids or other extrachromosomal DNA and these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a significant role in genetic diversity. In prokaryotes and viruses, the DNA is often densely packed and organized, in the case of archaea, by homologs to eukaryotic histones, small circular genomes called plasmids are often found in bacteria and also in mitochondria and chloroplasts, reflecting their bacterial origins. Some use the term chromosome in a sense, to refer to the individualized portions of chromatin in cells. However, others use the concept in a sense, to refer to the individualized portions of chromatin during cell division. The word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes, schleiden, Virchow and Bütschli were among the first scientists who recognized the structures now so familiar to everyone as chromosomes. The term was coined by von Waldeyer-Hartz, referring to the term chromatin, in a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes and it is the second of these principles that was so original
4.
DNA
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Deoxyribonucleic acid is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids, alongside proteins, lipids and complex carbohydrates, most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are termed polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases—cytosine, guanine, adenine, or thymine —a sugar called deoxyribose, and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037, in comparison the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information and this information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences, the two strands of DNA run in opposite directions to each other and are thus antiparallel. Attached to each sugar is one of four types of nucleobases and it is the sequence of these four nucleobases along the backbone that encodes biological information. RNA strands are created using DNA strands as a template in a process called transcription, under the genetic code, these RNA strands are translated to specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells DNA is organized into structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, eukaryotic organisms store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast prokaryotes store their DNA only in the cytoplasm, within the eukaryotic chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed, DNA was first isolated by Friedrich Miescher in 1869. DNA is used by researchers as a tool to explore physical laws and theories, such as the ergodic theorem. The unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro-, among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a polymer made from repeating units called nucleotides
5.
RNA
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Ribonucleic acid is a polymeric molecule essential in various biological roles in coding, decoding, regulation, and expression of genes. RNA and DNA are nucleic acids, and, along with proteins and carbohydrates, like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand. Cellular organisms use messenger RNA to convey information that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome, some RNA molecules play an active role within cells by catalyzing biological reactions, controlling gene expression, or sensing and communicating responses to cellular signals. One of these processes is protein synthesis, a universal function where RNA molecules direct the assembly of proteins on ribosomes. This process uses transfer RNA molecules to deliver amino acids to the ribosome, analysis of these RNAs has revealed that they are highly structured. Unlike DNA, their structures do not consist of long double helices, in this fashion, RNAs can achieve chemical catalysis. For instance, determination of the structure of the enzyme that catalyzes peptide bond formation—revealed that its active site is composed entirely of RNA. Each nucleotide in RNA contains a sugar, with carbons numbered 1 through 5. A base is attached to the 1 position, in general, adenine, cytosine, guanine, adenine and guanine are purines, cytosine and uracil are pyrimidines. A phosphate group is attached to the 3 position of one ribose, the phosphate groups have a negative charge each, making RNA a charged molecule. The bases form hydrogen bonds between cytosine and guanine, between adenine and uracil and between guanine and uracil, however, other interactions are possible, such as a group of adenine bases binding to each other in a bulge, or the GNRA tetraloop that has a guanine–adenine base-pair. An important structural feature of RNA that distinguishes it from DNA is the presence of a group at the 2 position of the ribose sugar. The A-form geometry results in a deep and narrow major groove. RNA is transcribed with only four bases, but these bases, pseudouridine, in which the linkage between uracil and ribose is changed from a C–N bond to a C–C bond, and ribothymidine are found in various places. Another notable modified base is hypoxanthine, a deaminated adenine base whose nucleoside is called inosine, inosine plays a key role in the wobble hypothesis of the genetic code. The specific roles of many of these modifications in RNA are not fully understood, the functional form of single-stranded RNA molecules, just like proteins, frequently requires a specific tertiary structure. The scaffold for this structure is provided by secondary structural elements that are hydrogen bonds within the molecule and this leads to several recognizable domains of secondary structure like hairpin loops, bulges, and internal loops
6.
Integrase
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Retroviral integrase is an enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell. Retroviral INs are not to be confused with phage integrases, such as λ phage integrase, IN is a key component in the retroviral pre-integration complex. The complex of integrase bound to cognate viral DNA ends has been referred to as the intasome, biochemical data and structural data suggest that retroviral IN functions as a tetramer. All three domains are important for multimerisation and viral DNA binding, early in 2010, scientists solved the crystal structure of IN from prototype foamy virus assembled on viral DNA ends. In addition, several host cellular proteins have shown to interact with IN to facilitate the integration process. Human chromatin-associated protein LEDGF, which tightly binds HIV IN and directs HIV PIC towards highly expressed genes for integration, is an example of such a host factor, integration occurs following production of the double-stranded viral DNA by the viral RNA/DNA-dependent DNA polymerase reverse transcriptase. The main function of IN is to insert the viral DNA into the host chromosomal DNA, integration is a point of no return for the cell, which becomes a permanent carrier of the viral genome. Integration is in responsible for the persistence of retroviral infections. After integration, the gene expression and particle production may take place immediately or at some point in the future. The timing, it is presumed, depends on the activity of the chromosomal locus hosting the provirus, the strand transfer reaction, in which the processed 3 ends of the viral DNA are covalently ligated to the host chromosomal DNA. Both reactions are catalysed by the active site and occur via transesterification, without a covalent protein-DNA intermediate, in contrast to reactions catalysed by Ser. HIV integrase is a 32 kDa protein produced from the C-terminal portion of the Pol gene product, in November 2005, data from a phase 2 study of an investigational HIV integrase inhibitor, MK-0518, demonstrated that the compound has potent antiviral activity. On October 12,2007, the Food and Drug Administration approved the integrase inhibitor Raltegravir, the second integrase inhibitor, elvitegravir, was approved in the U. S. in August 2012. The crystal structure of human foamy virus integrase has been examined successfully and this protein may use the morpheein model of allosteric regulation. Site-specific recombinase technology Integrases at the US National Library of Medicine Medical Subject Headings
7.
Germline
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However, there are many exceptions, including processes and concepts such as various forms of apomixis, autogamy, automixis, cloning, or parthenogenesis. The cells of the germline commonly are called germ cells, for example, gametes such as the sperm or the egg are part of the germline. In sexually reproducing organisms, cells that are not in the germline are called somatic cells, the term refers to all of the cells of body apart from the gametes. According to this view mutations, recombinations and other changes in the germline may be passed to offspring. This need not apply to somatically reproducing organisms, such as some Porifera, for example, many varieties of citrus, plants in the Rosaceae and some in the Asteraceae, such as Taraxacum produce seeds apomictically when somatic diploid cells displace the ovule or early embryo. Somatic cells of most organisms however, can only approach any such capability to a limited extent, many of his views necessarily changed during his life, and some of the resulting inconsistencies were discussed in depth by George Romanes. Plants and basal metazoans such as sponges and corals do not sequester a distinct germline and it is therefore likely that germline sequestration first evolved in complex animals with sophisticated body plans, i. e. bilaterians. There are several theories on the origin of the strict germline-soma distinction, setting aside an isolated germ cell population early in embryogenesis might promote cooperation between the somatic cells of a complex multicellular organism. August Weismann Epigenetics Germ line development Germinal choice technology Weismann barrier
8.
Bacteriophage
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A bacteriophage /ˈbækˈtɪər. i. oʊˌfeɪdʒ/ is a virus that infects and replicates within a bacterium. The term is derived from bacteria and the Greek, φαγεῖν, bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes, phages replicate within the bacterium following the injection of their genome into its cytoplasm. Bacteriophages are among the most common and diverse entities in the biosphere, phages are widely distributed in locations populated by bacterial hosts, such as soil or the intestines of animals. They have been used for over 90 years as an alternative to antibiotics in the former Soviet Union and Central Europe and they are seen as a possible therapy against multi-drug-resistant strains of many bacteria. Bacteriophages occur abundantly in the biosphere, with different virions, genomes, phages are classified by the International Committee on Taxonomy of Viruses according to morphology and nucleic acid. Nineteen families are recognized by the ICTV that infect bacteria. Of these, only two families have RNA genomes, and only five families are enveloped, of the viral families with DNA genomes, only two have single-stranded genomes. Eight of the families with DNA genomes have circular genomes while nine have linear genomes. Nine families infect bacteria only, nine infect archaea only, in 1915, British bacteriologist Frederick Twort, superintendent of the Brown Institution of London, discovered a small agent that infected and killed bacteria. He believed the agent must be one of the following, a stage in the cycle of the bacteria. Tworts work was interrupted by the onset of World War I, for d’Hérelle, there was no question as to the nature of his discovery, In a flash I had understood, what caused my clear spots was in fact an invisible microbe … a virus parasitic on bacteria. DHérelle called the virus a bacteriophage or bacteria-eater and he also recorded a dramatic account of a man suffering from dysentery who was restored to good health by the bacteriophages. It was DHerelle who conducted research into bacteriophages and introduced the concept of phage therapy. In 1969, Max Delbrück, Alfred Hershey and Salvador Luria were awarded the Nobel Prize in Physiology and Medicine for their discoveries of the replication of viruses and their genetic structure. Phages were discovered to be agents and were used in the former Soviet Republic of Georgia. They had widespread use, including treatment of soldiers in the Red Army, however, they were abandoned for general use in the West for several reasons, Medical trials were carried out, but a basic lack of understanding of phages made these invalid. Antibiotics were discovered and marketed widely and they were easier to make, store and to prescribe
9.
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
10.
Lysogenic cycle
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Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the nucleic acid into the host bacteriums genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally, lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood. The key difference between the cycle and the lysogenic cycle is that the lysogenic cycle does not lyse the host cell. Phages that replicate only via the cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages. In the lysogenic cycle, the phage DNA first integrates into the chromosome to produce the prophage. When the bacterium reproduces, the prophage is also copied and is present in each of the daughter cells, the daughter cells can continue to replicate with the prophage present or the prophage can exit the bacterial chromosome to initiate the lytic cycle. Bacteriophages are viruses that infect and replicate within a bacterium, temperate phages can reproduce using both the lytic and the lysogenic cycle. Via the lysogenic cycle, the genome is not expressed and is instead integrated into the bacterias genome to form the prophage. In this scenario, the daughter bacteria cells contain prophage and are known as lysogens, lysogens can remain in the lysogenic cycle for many generations but can switch to the lytic cycle at any time via a process known as induction. During induction, prophage DNA is excised from the genome and is transcribed and translated to make coat proteins for the virus. The model organism for studying lysogeny is lambda phage, prophage integration, maintenance of lysogeny, induction, and control of phage genome excision in induction is described in detail in the lambda phage article. Bacteriophages are parasitic because they infect their hosts, use bacterial machinery to replicate, temperate phages can lead to both advantages and disadvantages for their hosts via the lysogenic cycle. During the lysogenic cycle, the genome is incorporated as prophage. Nonetheless, a temperate phage can escape repression to replicate, produce viral particles, the temperate phage escaping repression would be a disadvantage for the bacteria. On the other hand, the prophage may transfer genes that enhance host virulence and resistance to the immune system, also, the repressor produced by the prophage that prevents prophage genes from being expressed confers an immunity for the host bacteria from lytic infection by related viruses. In some interactions between lysogenic phages and bacteria, lysogenic conversion may occur, which can also be called phage conversion and it is when a temperate phage induces a change in the phenotype of the infected bacteria that is not part of a usual phage cycle. Changes can often involve the external membrane of the cell by making it impervious to other phages or even by increasing the capability of the bacteria for a host
11.
Reverse transcriptase
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A reverse transcriptase is an enzyme used to generate complementary DNA from an RNA template, a process termed reverse transcription. It is mainly associated with retroviruses, RT inhibitors are widely used as antiretroviral drugs. RT activities are associated with the replication of chromosome ends. Retroviral RT has three sequential biochemical activities, RNA-dependent DNA polymerase activity, ribonuclease H, and DNA-dependent DNA polymerase activity. The same sequence of reactions is used in the laboratory to convert RNA to DNA for use in molecular cloning, RNA sequencing, polymerase chain reaction. Well studied reverse transcriptases include, HIV-1 reverse transcriptase from human immunodeficiency virus type 1 has two subunits, which have respective molecular weights of 66 and 51 kDa, M-MLV reverse transcriptase from the Moloney murine leukemia virus is a single 75 kDa monomer. AMV reverse transcriptase from the avian myeloblastosis virus also has two subunits, a 63 kDa subunit and a 95 kDa subunit, telomerase reverse transcriptase that maintains the telomeres of eukaryotic chromosomes. For their achievements, both shared the 1975 Nobel Prize in Physiology or Medicine, the enzymes are encoded and used by reverse-transcribing viruses, which use the enzyme during the process of replication. Reverse-transcribing RNA viruses, such as retroviruses, use the enzyme to reverse-transcribe their RNA genomes into DNA, reverse-transcribing DNA viruses, such as the hepadnaviruses, can allow RNA to serve as a template in assembling and making DNA strands. HIV infects humans with the use of this enzyme, without reverse transcriptase, the viral genome would not be able to incorporate into the host cell, resulting in failure to replicate. Reverse transcriptase creates single-stranded DNA from an RNA template, the process of reverse transcription is extremely error-prone, and it is during this step that mutations may occur. Such mutations may cause drug resistance, retroviruses, also referred to as class VI ssRNA-RT viruses, are RNA reverse-transcribing viruses with a DNA intermediate. Their genomes consist of two molecules of positive-sense single-stranded RNA with a 5 cap and 3 polyadenylated tail, examples of retroviruses include the human immunodeficiency virus and the human T-lymphotropic virus. Complementary DNA then binds to the U5 and R region of the viral RNA, a domain on the reverse transcriptase enzyme called RNAse H degrades the 5’ end of the RNA which removes the U5 and R region. The primer then jumps to the 3’ end of the genome. The first strand of complementary DNA is extended, and the majority of viral RNA is degraded by RNAse H, once the strand is completed, second strand synthesis is initiated from the viral RNA. There is then another jump where the PBS from the second strand hybridizes with the complementary PBS on the first strand, both strands are extended further and can be incorporated into the hosts genome by the enzyme integrase. Retroviral RNA is arranged in 5’ terminus to 3’ terminus, the site where the primer is annealed to viral RNA is called the primer-binding site
12.
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
. PMID 15044706.
