142-753: See text Poxviridae is a family of double-stranded DNA viruses . Vertebrates and arthropods serve as natural hosts. There are currently 83 species in this family, divided among 22 genera, which are divided into two subfamilies. Diseases associated with this family include smallpox . Four genera of poxviruses may infect humans: Orthopoxvirus , Parapoxvirus , Yatapoxvirus , Molluscipoxvirus . Orthopoxvirus : smallpox virus (variola), vaccinia virus, cowpox virus, Mpox virus; Parapoxvirus : orf virus, pseudocowpox , bovine papular stomatitis virus; Yatapoxvirus : tanapox virus, yaba monkey tumor virus ; Molluscipoxvirus : molluscum contagiosum virus (MCV). The most common are vaccinia (seen on
284-430: A big potential to modify the genetic control in a host organism. The movement of TEs is a driving force of genome evolution in eukaryotes because their insertion can disrupt gene functions, homologous recombination between TEs can produce duplications, and TE can shuffle exons and regulatory sequences to new locations. Retrotransposons are found mostly in eukaryotes but not found in prokaryotes. Retrotransposons form
426-445: A buffer to recruit or titrate ions or antibiotics. Extracellular DNA acts as a functional extracellular matrix component in the biofilms of several bacterial species. It may act as a recognition factor to regulate the attachment and dispersal of specific cell types in the biofilm; it may contribute to biofilm formation; and it may contribute to the biofilm's physical strength and resistance to biological stress. Cell-free fetal DNA
568-462: A cell makes up its genome ; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes. The information carried by DNA is held in the sequence of pieces of DNA called genes . Transmission of genetic information in genes is achieved via complementary base pairing. For example, in transcription, when a cell uses the information in a gene, the DNA sequence is copied into
710-450: A chain by covalent bonds (known as the phosphodiester linkage ) 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 separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G), with hydrogen bonds to make double-stranded DNA. The complementary nitrogenous bases are divided into two groups,
852-445: A complementary RNA sequence through the attraction between the DNA and the correct RNA nucleotides. Usually, this RNA copy is then used to make a matching protein sequence in a process called translation , which depends on the same interaction between RNA nucleotides. In an alternative fashion, a cell may copy its genetic information in a process called DNA replication . The details of these functions are covered in other articles; here
994-506: A defined structure that are able to change their location in the genome. TEs are categorized as either as a mechanism that replicates by copy-and-paste or as a mechanism that can be excised from the genome and inserted at a new location. In the human genome, there are three important classes of TEs that make up more than 45% of the human DNA; these classes are The long interspersed nuclear elements (LINEs), The interspersed nuclear elements (SINEs), and endogenous retroviruses. These elements have
1136-492: A double helix can thus be pulled apart like a zipper, either by a mechanical force or high temperature . As a result of this base pair complementarity, all the information in the double-stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication. This reversible and specific interaction between complementary base pairs is critical for all the functions of DNA in organisms. Most DNA molecules are actually two polymer strands, bound together in
1278-428: A full set of the mitochondrial genes. Each human mitochondrion contains, on average, approximately 5 such mtDNA molecules. Each human cell contains approximately 100 mitochondria, giving a total number of mtDNA molecules per human cell of approximately 500. However, the amount of mitochondria per cell also varies by cell type, and an egg cell can contain 100,000 mitochondria, corresponding to up to 1,500,000 copies of
1420-439: A helical fashion by noncovalent bonds; this double-stranded (dsDNA) structure is maintained largely by the intrastrand base stacking interactions, which are strongest for G,C stacks. The two strands can come apart—a process known as melting—to form two single-stranded DNA (ssDNA) molecules. Melting occurs at high temperatures, low salt and high pH (low pH also melts DNA, but since DNA is unstable due to acid depurination, low pH
1562-571: A higher number is also possible but this would be against the natural principle of least effort . The phosphate groups of DNA give it similar acidic properties to phosphoric acid and it can be considered as a strong acid . It will be fully ionized at a normal cellular pH, releasing protons which leave behind negative charges on the phosphate groups. These negative charges protect DNA from breakdown by hydrolysis by repelling nucleophiles which could hydrolyze it. Pure DNA extracted from cells forms white, stringy clumps. The expression of genes
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#17327870206471704-459: A human disease which suggests a relatively recent origin. However, if the mutation rate is assumed to be similar to that of the herpesviruses the divergence date between variola from Taterapox has been estimated to be 50,000 years ago. While this is consistent with the other published estimates it suggests that the archaeological and historical evidence is very incomplete. Better estimates of mutation rates in these viruses are needed. The species in
1846-534: A large portion of the genomes of many eukaryotes. A retrotransposon is a transposable element that transposes through an RNA intermediate. Retrotransposons are composed of DNA , but are transcribed into RNA for transposition, then the RNA transcript is copied back to DNA formation with the help of a specific enzyme called reverse transcriptase. A retrotransposon that carries reverse transcriptase in its sequence can trigger its own transposition but retrotransposons that lack
1988-667: A long-standing puzzle known as the " C-value enigma ". However, some DNA sequences that do not code protein may still encode functional non-coding RNA molecules, which are involved in the regulation of gene expression . Some noncoding DNA sequences play structural roles in chromosomes. Telomeres and centromeres typically contain few genes but are important for the function and stability of chromosomes. An abundant form of noncoding DNA in humans are pseudogenes , which are copies of genes that have been disabled by mutation. These sequences are usually just molecular fossils , although they can occasionally serve as raw genetic material for
2130-405: A main driving role to generate genetic novelty and natural genome editing. Works of science fiction illustrate concerns about the availability of genome sequences. Michael Crichton's 1990 novel Jurassic Park and the subsequent film tell the story of a billionaire who creates a theme park of cloned dinosaurs on a remote island, with disastrous outcomes. A geneticist extracts dinosaur DNA from
2272-413: A major role in shaping the genome. Duplication may range from extension of short tandem repeats , to duplication of a cluster of genes, and all the way to duplication of entire chromosomes or even entire genomes . Such duplications are probably fundamental to the creation of genetic novelty. Horizontal gene transfer is invoked to explain how there is often an extreme similarity between small portions of
2414-467: A major theme of the book. The 1997 film Gattaca is set in a futurist society where genomes of children are engineered to contain the most ideal combination of their parents' traits, and metrics such as risk of heart disease and predicted life expectancy are documented for each person based on their genome. People conceived outside of the eugenics program, known as "In-Valids" suffer discrimination and are relegated to menial occupations. The protagonist of
2556-409: A narrower, deeper major groove. The A form occurs under non-physiological conditions in partly dehydrated samples of DNA, while in the cell it may be produced in hybrid pairings of DNA and RNA strands, and in enzyme-DNA complexes. Segments of DNA where the bases have been chemically modified by methylation may undergo a larger change in conformation and adopt the Z form . Here, the strands turn about
2698-428: A new site. This cut-and-paste mechanism typically reinserts transposons near their original location (within 100 kb). DNA transposons are found in bacteria and make up 3% of the human genome and 12% of the genome of the roundworm C. elegans . Genome size is the total number of the DNA base pairs in one copy of a haploid genome. Genome size varies widely across species. Invertebrates have small genomes, this
2840-562: A new squirrel poxvirus in Berlin, Germany. The date of the appearance of smallpox is not settled. It most likely evolved from a rodent virus between 68,000 and 16,000 years ago. The wide range of dates is due to the different records used to calibrate the molecular clock. One clade was the variola major strains (the more clinically severe form of smallpox) which spread from Asia between 400 and 1,600 years ago. A second clade included both alastrim minor (a phenotypically mild smallpox) described from
2982-402: A number of unclassified species for which new genera may be created in the future. The prototypical poxvirus is vaccinia virus , known for its role in the eradication of smallpox. The vaccinia virus is an effective tool for foreign protein expression, as it elicits a strong host immune-response. The vaccinia virus enters cells primarily by cell fusion, although currently the receptor responsible
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#17327870206473124-442: A radius of 10 Å (1.0 nm). According to another study, when measured in a different solution, the DNA chain measured 22–26 Å (2.2–2.6 nm) wide, and one nucleotide unit measured 3.3 Å (0.33 nm) long. The buoyant density of most DNA is 1.7g/cm . DNA does not usually exist as a single strand, but instead as a pair of strands that are held tightly together. These two long strands coil around each other, in
3266-415: A reference, whereas analyses of coverage depth and mapping topology can provide details regarding structural variations such as chromosomal translocations and segmental duplications. DNA sequences that carry the instructions to make proteins are referred to as coding sequences. The proportion of the genome occupied by coding sequences varies widely. A larger genome does not necessarily contain more genes, and
3408-415: A relatively high G+C content. The reasons for these differences are not known. Replication of the poxvirus involves several stages. The virus first binds to a receptor on the host cell surface; the receptors for the poxvirus are thought to be glycosaminoglycans . After binding to the receptor, the virus enters the cell where it uncoats. Uncoating of the virus is a two step process. Firstly the outer membrane
3550-487: A reverse transcriptase must use reverse transcriptase synthesized by another retrotransposon. Retrotransposons can be transcribed into RNA, which are then duplicated at another site into the genome. Retrotransposons can be divided into long terminal repeats (LTRs) and non-long terminal repeats (Non-LTRs). Long terminal repeats (LTRs) are derived from ancient retroviral infections, so they encode proteins related to retroviral proteins including gag (structural proteins of
3692-416: A second protein when read in the opposite direction along the other strand. In bacteria , this overlap may be involved in the regulation of gene transcription, while in viruses, overlapping genes increase the amount of information that can be encoded within the small viral genome. DNA can be twisted like a rope in a process called DNA supercoiling . With DNA in its "relaxed" state, a strand usually circles
3834-445: A simple TTAGGG sequence. These guanine-rich sequences may stabilize chromosome ends by forming structures of stacked sets of four-base units, rather than the usual base pairs found in other DNA molecules. Here, four guanine bases, known as a guanine tetrad , form a flat plate. These flat four-base units then stack on top of each other to form a stable G-quadruplex structure. These structures are stabilized by hydrogen bonding between
3976-404: A single, linear molecule of DNA, but some are made up of a circular DNA molecule. Prokaryotes and eukaryotes have DNA genomes. Archaea and most bacteria have a single circular chromosome , however, some bacterial species have linear or multiple chromosomes. If the DNA is replicated faster than the bacterial cells divide, multiple copies of the chromosome can be present in a single cell, and if
4118-414: A single, linear, double-stranded segment of DNA. By comparison, rhinoviruses are 1/10 as large as a typical Poxviridae virion. Phylogenetic analysis of 26 different chordopoxvirus genomes has shown that the central region of the genome is conserved and contains ~90 genes. The termini in contrast are not conserved between species. Of this group Avipoxvirus is the most divergent. The next most divergent
4260-646: A species related to both the poxviruses and the adenoviruses. Based on the genome organisation and DNA replication mechanism a phylogenetic relationships may exist between the rudiviruses ( Rudiviridae ) and the large eukaryal DNA viruses: the African swine fever virus ( Asfarviridae ), Chlorella viruses ( Phycodnaviridae ) and poxviruses ( Poxviridae ). The mutation rate in poxvirus genomes has been estimated to be 0.9–1.2 x 10 substitutions per site per year. A second estimate puts this rate at 0.5–7 × 10 nucleotide substitutions per site per year. A third estimate places
4402-424: A vocabulary into which genome fits systematically. It is very difficult to come up with a precise definition of "genome." It usually refers to the DNA (or sometimes RNA) molecules that carry the genetic information in an organism but sometimes it is difficult to decide which molecules to include in the definition; for example, bacteria usually have one or two large DNA molecules ( chromosomes ) that contain all of
Poxviridae - Misplaced Pages Continue
4544-537: Is Molluscipoxvirus. Capripoxvirus, Leporipoxvirus, Suipoxvirus and Yatapoxvirus genera cluster together: Capripoxvirus and Suipoxvirus share a common ancestor and are distinct from the genus Orthopoxvirus. Within the Othopoxvirus genus Cowpox virus strain Brighton Red, Ectromelia virus and Mpox virus do not group closely with any other member. Variola virus and Camelpox virus form a subgroup. Vaccinia virus
4686-485: Is also correlated to a small number of transposable elements. Fish and Amphibians have intermediate-size genomes, and birds have relatively small genomes but it has been suggested that birds lost a substantial portion of their genomes during the phase of transition to flight. Before this loss, DNA methylation allows the adequate expansion of the genome. In humans, the nuclear genome comprises approximately 3.1 billion nucleotides of DNA, divided into 24 linear molecules,
4828-432: Is another DIRS-like elements belong to Non-LTRs. Non-LTRs are widely spread in eukaryotic genomes. Long interspersed elements (LINEs) encode genes for reverse transcriptase and endonuclease, making them autonomous transposable elements. The human genome has around 500,000 LINEs, taking around 17% of the genome. Short interspersed elements (SINEs) are usually less than 500 base pairs and are non-autonomous, so they rely on
4970-455: Is based on phenotypic characteristics; morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. The smallpox virus remains the most notable member of the family. Diseases caused by pox viruses, especially smallpox, have been known about for centuries. One of the earliest suspected cases is that of Egyptian pharaoh Ramses V who is thought to have died from smallpox circa 1150 years BCE. Smallpox
5112-447: Is called intercalation . Most intercalators are aromatic and planar molecules; examples include ethidium bromide , acridines , daunomycin , and doxorubicin . For an intercalator to fit between base pairs, the bases must separate, distorting the DNA strands by unwinding of the double helix. This inhibits both transcription and DNA replication, causing toxicity and mutations. As a result, DNA intercalators may be carcinogens , and in
5254-435: Is called a polynucleotide . The backbone of the DNA strand is made from alternating phosphate and sugar groups. The sugar in DNA is 2-deoxyribose , which is a pentose (five- carbon ) sugar. The sugars are joined by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These are known as the 3′-end (three prime end), and 5′-end (five prime end) carbons,
5396-444: Is carried in plasmids . For this, the word genome should not be used as a synonym of chromosome . Eukaryotic genomes are composed of one or more linear DNA chromosomes. The number of chromosomes varies widely from Jack jumper ants and an asexual nemotode , which each have only one pair, to a fern species that has 720 pairs. It is surprising the amount of DNA that eukaryotic genomes contain compared to other genomes. The amount
5538-434: Is dependent on ionic strength and the concentration of DNA. As a result, it is both the percentage of GC base pairs and the overall length of a DNA double helix that determines the strength of the association between the two strands of DNA. Long DNA helices with a high GC -content have more strongly interacting strands, while short helices with high AT content have more weakly interacting strands. In biology, parts of
5680-564: Is even more than what is necessary for DNA protein-coding and noncoding genes due to the fact that eukaryotic genomes show as much as 64,000-fold variation in their sizes. However, this special characteristic is caused by the presence of repetitive DNA, and transposable elements (TEs). A typical human cell has two copies of each of 22 autosomes , one inherited from each parent, plus two sex chromosomes , making it diploid. Gametes , such as ova, sperm, spores, and pollen, are haploid, meaning they carry only one copy of each chromosome. In addition to
5822-492: Is facilitated by active DNA demethylation , a process that entails the DNA base excision repair pathway. This pathway is employed in the erasure of CpG methylation (5mC) in primordial germ cells. The erasure of 5mC occurs via its conversion to 5-hydroxymethylcytosine (5hmC) driven by high levels of the ten-eleven dioxygenase enzymes TET1 and TET2 . Genomes are more than the sum of an organism's genes and have traits that may be measured and studied without reference to
Poxviridae - Misplaced Pages Continue
5964-480: Is found in the blood of the mother, and can be sequenced to determine a great deal of information about the developing fetus. Genome In the fields of molecular biology and genetics , a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses ). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of
6106-440: Is growing rapidly. The US National Institutes of Health maintains one of several comprehensive databases of genomic information. Among the thousands of completed genome sequencing projects include those for rice , a mouse , the plant Arabidopsis thaliana , the puffer fish , and the bacteria E. coli . In December 2013, scientists first sequenced the entire genome of a Neanderthal , an extinct species of humans . The genome
6248-411: Is influenced by how the DNA is packaged in chromosomes, in a structure called chromatin . Base modifications can be involved in packaging, with regions that have low or no gene expression usually containing high levels of methylation of cytosine bases. DNA packaging and its influence on gene expression can also occur by covalent modifications of the histone protein core around which DNA is wrapped in
6390-432: Is introduced by enzymes called topoisomerases . These enzymes are also needed to relieve the twisting stresses introduced into DNA strands during processes such as transcription and DNA replication . DNA exists in many possible conformations that include A-DNA , B-DNA , and Z-DNA forms, although only B-DNA and Z-DNA have been directly observed in functional organisms. The conformation that DNA adopts depends on
6532-416: Is most closely related to CPV-GRI-90. The GC-content of family member genomes differ considerably. Avipoxvirus, capripoxvirus, cervidpoxvirus, orthopoxvirus, suipoxvirus, yatapoxvirus and one Entomopox genus (Betaentomopoxvirus) along with several other unclassified Entomopoxviruses have a low G+C content while others - Molluscipoxvirus, Orthopoxvirus, Parapoxvirus and some unclassified Chordopoxvirus - have
6674-422: Is nothing special about the four natural nucleobases that evolved on Earth. On the other hand, DNA is tightly related to RNA which does not only act as a transcript of DNA but also performs as molecular machines many tasks in cells. For this purpose it has to fold into a structure. It has been shown that to allow to create all possible structures at least four bases are required for the corresponding RNA , while
6816-432: Is one of four types of nucleobases (or bases ). It is the sequence of these four nucleobases along the backbone that encodes genetic information. RNA strands are created using DNA strands as a template in a process called transcription , where DNA bases are exchanged for their corresponding bases except in the case of thymine (T), for which RNA substitutes uracil (U). Under the genetic code , these RNA strands specify
6958-517: Is rarely used). The stability of the dsDNA form depends not only on the GC -content (% G,C basepairs) but also on sequence (since stacking is sequence specific) and also length (longer molecules are more stable). The stability can be measured in various ways; a common way is the melting temperature (also called T m value), which is the temperature at which 50% of the double-strand molecules are converted to single-strand molecules; melting temperature
7100-401: Is rather exceptional, eukaryotes generally have these features in their genes and their genomes contain variable amounts of repetitive DNA. In mammals and plants, the majority of the genome is composed of repetitive DNA. High-throughput technology makes sequencing to assemble new genomes accessible to everyone. Sequence polymorphisms are typically discovered by comparing resequenced isolates to
7242-428: Is recreated by an enzyme called DNA polymerase . This enzyme makes the complementary strand by finding the correct base through complementary base pairing and bonding it onto the original strand. As DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms are used to copy the antiparallel strands of the double helix. In this way, the base on the old strand dictates which base appears on
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#17327870206477384-614: Is released as external enveloped virion. DNA Deoxyribonucleic acid ( / d iː ˈ ɒ k s ɪ ˌ r aɪ b oʊ nj uː ˌ k l iː ɪ k , - ˌ k l eɪ -/ ; DNA ) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix . The polymer carries genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses . DNA and ribonucleic acid (RNA) are nucleic acids . Alongside proteins , lipids and complex carbohydrates ( polysaccharides ), nucleic acids are one of
7526-425: Is removed as the particle enters the cell; secondly the virus particle (without the outer membrane) fuses with the cellular membrane to release the core into the cytoplasm. The pox viral genes are expressed in two phases. The early genes encode the non-structural protein, including proteins necessary for replication of the viral genome, and are expressed before the genome is replicated. The late genes are expressed after
7668-462: Is the complete list of the nucleotides (A, C, G, and T for DNA genomes) that make up all the chromosomes of an individual or a species. Within a species, the vast majority of nucleotides are identical between individuals, but sequencing multiple individuals is necessary to understand the genetic diversity. In 1976, Walter Fiers at the University of Ghent (Belgium) was the first to establish
7810-516: Is the largest human chromosome with approximately 220 million base pairs , and would be 85 mm long if straightened. In eukaryotes , in addition to nuclear DNA , there is also mitochondrial DNA (mtDNA) which encodes certain proteins used by the mitochondria. The mtDNA is usually relatively small in comparison to the nuclear DNA. For example, the human mitochondrial DNA forms closed circular molecules, each of which contains 16,569 DNA base pairs, with each such molecule normally containing
7952-489: Is to allow the cell to replicate chromosome ends using the enzyme telomerase , as the enzymes that normally replicate DNA cannot copy the extreme 3′ ends of chromosomes. These specialized chromosome caps also help protect the DNA ends, and stop the DNA repair systems in the cell from treating them as damage to be corrected. In human cells , telomeres are usually lengths of single-stranded DNA containing several thousand repeats of
8094-421: Is to reduce the number of genes in a genome to the bare minimum and still have the organism in question survive. There is experimental work being done on minimal genomes for single cell organisms as well as minimal genomes for multi-cellular organisms (see developmental biology ). The work is both in vivo and in silico . There are many enormous differences in size in genomes, specially mentioned before in
8236-408: Is unknown. Vaccinia contains three classes of genes: early, intermediate and late. These genes are transcribed by viral RNA polymerase and associated transcription factors. Vaccinia replicates its genome in the cytoplasm of infected cells, and after late-stage gene expression undergoes virion morphogenesis, which produces intracellular mature virions contained within an envelope membrane. The origin of
8378-657: The DNA sequence . Mutagens include oxidizing agents , alkylating agents and also high-energy electromagnetic radiation such as ultraviolet light and X-rays . The type of DNA damage produced depends on the type of mutagen. For example, UV light can damage DNA by producing thymine dimers , which are cross-links between pyrimidine bases. On the other hand, oxidants such as free radicals or hydrogen peroxide produce multiple forms of damage, including base modifications, particularly of guanosine, and double-strand breaks. A typical human cell contains about 150,000 bases that have suffered oxidative damage. Of these oxidative lesions,
8520-601: The Genoscope in Paris. Reference genome sequences and maps continue to be updated, removing errors and clarifying regions of high allelic complexity. The decreasing cost of genomic mapping has permitted genealogical sites to offer it as a service, to the extent that one may submit one's genome to crowdsourced scientific endeavours such as DNA.LAND at the New York Genome Center , an example both of
8662-664: The Orthopoxvirus into the extant genera occurred ~14,000 years ago. The genus Leporipoxvirus diverged ~137,000 ± 35,000 years ago. This was followed by the ancestor of the genus Yatapoxvirus . The last common ancestor of the Capripoxvirus and Suipoxvirus diverged 111,000 ± 29,000 years ago. An isolate from a fish – salmon gill poxvirus – appears to be the earliest branch in the Chordopoxvirinae . A new systematic has been proposed recently after findings of
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#17327870206478804-406: The amino-acid sequences of proteins is determined by the rules of translation , known collectively as the genetic code . The genetic code consists of three-letter 'words' called codons formed from a sequence of three nucleotides (e.g. ACT, CAG, TTT). In transcription, the codons of a gene are copied into messenger RNA by RNA polymerase . This RNA copy is then decoded by a ribosome that reads
8946-469: The cell nucleus as nuclear DNA , and some in the mitochondria as mitochondrial DNA or in chloroplasts as chloroplast DNA . In contrast, prokaryotes ( bacteria and archaea ) store their DNA only in the cytoplasm , in circular chromosomes . Within eukaryotic chromosomes, chromatin proteins, such as histones , compact and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of
9088-406: The economies of scale and of citizen science . Viral genomes can be composed of either RNA or DNA. The genomes of RNA viruses can be either single-stranded RNA or double-stranded RNA , and may contain one or more separate RNA molecules (segments: monopartit or multipartit genome). DNA viruses can have either single-stranded or double-stranded genomes. Most DNA virus genomes are composed of
9230-426: The intracellular mature virion form of the virus, which contains different envelope, is also infectious. They vary in their shape depending upon the species but are generally shaped like a brick or as an oval form similar to a rounded brick because they are wrapped by the endoplasmic reticulum. The virion is exceptionally large, its size is around 200 nm in diameter and 300 nm in length and carries its genome in
9372-455: The mitochondria . In addition, algae and plants have chloroplast DNA. Most textbooks make a distinction between the nuclear genome and the organelle (mitochondria and chloroplast) genomes so when they speak of, say, the human genome, they are only referring to the genetic material in the nucleus. This is the most common use of 'genome' in the scientific literature. Most eukaryotes are diploid , meaning that there are two of each chromosome in
9514-423: The 16 chromosomes of budding yeast Saccharomyces cerevisiae published as the result of a European-led effort begun in the mid-1980s. 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 genome sequencing dramatically cheaper and easier, and the number of complete genome sequences
9656-419: The 3′ and 5′ carbons along the sugar-phosphate backbone confers directionality (sometimes called polarity) to each DNA strand. In a nucleic acid double helix , the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel . The asymmetric ends of DNA strands are said to have a directionality of five prime end (5′ ), and three prime end (3′), with
9798-542: The 5′ end having a terminal phosphate group and the 3′ end a terminal hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the related pentose sugar ribose in RNA. The DNA double helix is stabilized primarily by two forces: hydrogen bonds between nucleotides and base-stacking interactions among aromatic nucleobases. The four bases found in DNA are adenine ( A ), cytosine ( C ), guanine ( G ) and thymine ( T ). These four bases are attached to
9940-467: The American continents and isolates from West Africa which diverged from an ancestral strain between 1,400 and 6,300 years before present. This clade further diverged into two subclades at least 800 years ago. A second estimate has placed the separation of variola from Taterapox at 3000–4000 years ago. This is consistent with archaeological and historical evidence regarding the appearance of smallpox as
10082-435: The DNA are transcribed. DNA is a long polymer made from repeating units called nucleotides . The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds . Both chains are coiled around the same axis, and have the same pitch of 34 ångströms (3.4 nm ). The pair of chains have
10224-460: The DNA double helix that need to separate easily, such as the TATAAT Pribnow box in some promoters , tend to have a high AT content, making the strands easier to pull apart. In the laboratory, the strength of this interaction can be measured by finding the melting temperature T m necessary to break half of the hydrogen bonds. When all the base pairs in a DNA double helix melt,
10366-486: The Indian subcontinent) and molluscum contagiosum, but Mpox infections are rising (seen in west and central African rainforest countries). The similarly named disease chickenpox is not a true poxvirus and is caused by the herpesvirus varicella zoster . The name of the family, Poxviridae , is a legacy of the original grouping of viruses associated with diseases that produced poxes on the skin. Modern viral classification
10508-401: The RNA sequence by base-pairing the messenger RNA to transfer RNA , which carries amino acids. Since there are 4 bases in 3-letter combinations, there are 64 possible codons (4 combinations). These encode the twenty standard amino acids , giving most amino acids more than one possible codon. There are also three 'stop' or 'nonsense' codons signifying the end of the coding region; these are
10650-491: The TAG, TAA, and TGA codons, (UAG, UAA, and UGA on the mRNA). Cell division is essential for an organism to grow, but, when a cell divides, it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. The double-stranded structure of DNA provides a simple mechanism for DNA replication . Here, the two strands are separated and then each strand's complementary DNA sequence
10792-442: The axis of the double helix once every 10.4 base pairs, but if the DNA is twisted the strands become more tightly or more loosely wound. If the DNA is twisted in the direction of the helix, this is positive supercoiling, and the bases are held more tightly together. If they are twisted in the opposite direction, this is negative supercoiling, and the bases come apart more easily. In nature, most DNA has slight negative supercoiling that
10934-412: The blood of ancient mosquitoes and fills in the gaps with DNA from modern species to create several species of dinosaurs. A chaos theorist is asked to give his expert opinion on the safety of engineering an ecosystem with the dinosaurs, and he repeatedly warns that the outcomes of the project will be unpredictable and ultimately uncontrollable. These warnings about the perils of using genomic information are
11076-407: The canonical bases plus uracil. Twin helical strands form the DNA backbone. Another double helix may be found tracing the spaces, or grooves, between the strands. These voids are adjacent to the base pairs and may provide a binding site . As the strands are not symmetrically located with respect to each other, the grooves are unequally sized. The major groove is 22 ångströms (2.2 nm) wide, while
11218-467: The case of thalidomide, a teratogen . Others such as benzo[ a ]pyrene diol epoxide and aflatoxin form DNA adducts that induce errors in replication. Nevertheless, due to their ability to inhibit DNA transcription and replication, other similar toxins are also used in chemotherapy to inhibit rapidly growing cancer cells. DNA usually occurs as linear chromosomes in eukaryotes , and circular chromosomes in prokaryotes . The set of chromosomes in
11360-581: The cell (see below) , but the major and minor grooves are always named to reflect the differences in width that would be seen if the DNA was twisted back into the ordinary B form . In a DNA double helix, each type of nucleobase on one strand bonds with just one type of nucleobase on the other strand. This is called complementary base pairing . Purines form hydrogen bonds to pyrimidines, with adenine bonding only to thymine in two hydrogen bonds, and cytosine bonding only to guanine in three hydrogen bonds. This arrangement of two nucleotides binding together across
11502-549: The cells divide faster than the DNA can be replicated, multiple replication of the chromosome is initiated before the division occurs, allowing daughter cells to inherit complete genomes and already partially replicated chromosomes. Most prokaryotes have very little repetitive DNA in their genomes. However, some symbiotic bacteria (e.g. Serratia symbiotica ) have reduced genomes and a high fraction of pseudogenes: only ~40% of their DNA encodes proteins. Some bacteria have auxiliary genetic material, also part of their genome, which
11644-619: The chromatin structure or else by remodeling carried out by chromatin remodeling complexes (see Chromatin remodeling ). There is, further, crosstalk between DNA methylation and histone modification, so they can coordinately affect chromatin and gene expression. For one example, cytosine methylation produces 5-methylcytosine , which is important for X-inactivation of chromosomes. The average level of methylation varies between organisms—the worm Caenorhabditis elegans lacks cytosine methylation, while vertebrates have higher levels, with up to 1% of their DNA containing 5-methylcytosine. Despite
11786-478: The chromosomes in the nucleus, organelles such as the chloroplasts and mitochondria have their own DNA. Mitochondria are sometimes said to have their own genome often referred to as the " mitochondrial genome ". The DNA found within the chloroplast may be referred to as the " plastome ". Like the bacteria they originated from, mitochondria and chloroplasts have a circular chromosome. Unlike prokaryotes where exon-intron organization of protein coding genes exists but
11928-455: The co-discoverers of the structure of DNA. Whereas a genome sequence lists the order of every DNA base in a genome, a genome map identifies the landmarks. A genome map is less detailed than a genome sequence and aids in navigating around the genome. The Human Genome Project was organized to map and to sequence the human genome . A fundamental step in the project was the release of a detailed genomic map by Jean Weissenbach and his team at
12070-415: The complete nucleotide sequence of a viral RNA-genome ( Bacteriophage MS2 ). The next year, Fred Sanger completed the first DNA-genome sequence: Phage Φ-X174 , of 5386 base pairs. The first bacterial genome to be sequenced was that of Haemophilus influenzae , completed by a team at The Institute for Genomic Research in 1995. A few months later, the first eukaryotic genome was completed, with sequences of
12212-480: The conditions found in cells, it is not a well-defined conformation but a family of related DNA conformations that occur at the high hydration levels present in cells. Their corresponding X-ray diffraction and scattering patterns are characteristic of molecular paracrystals with a significant degree of disorder. Compared to B-DNA, the A-DNA form is a wider right-handed spiral, with a shallow, wide minor groove and
12354-405: The creation of new genes through the process of gene duplication and divergence . A gene is a sequence of DNA that contains genetic information and can influence the phenotype of an organism. Within a gene, the sequence of bases along a DNA strand defines a messenger RNA sequence, which then defines one or more protein sequences. The relationship between the nucleotide sequences of genes and
12496-449: The cytoplasm called the nucleoid . The genetic information in a genome is held within genes, and the complete set of this information in an organism is called its genotype . A gene is a unit of heredity and is a region of DNA that influences a particular characteristic in an organism. Genes contain an open reading frame that can be transcribed, and regulatory sequences such as promoters and enhancers , which control transcription of
12638-421: The cytoplasm possible. Most double-stranded DNA viruses require the host cell's DNA-dependent RNA polymerase to perform transcription. These host polymerases are found in the nucleus , and therefore most double-stranded DNA viruses carry out a part of their infection cycle within the host cell's nucleus. The ancestor of the poxviruses is not known but structural studies suggest it may have been an adenovirus or
12780-445: The details of any particular genes and their products. Researchers compare traits such as karyotype (chromosome number), genome size , gene order, codon usage bias , and GC-content to determine what mechanisms could have produced the great variety of genomes that exist today (for recent overviews, see Brown 2002; Saccone and Pesole 2003; Benfey and Protopapas 2004; Gibson and Muse 2004; Reese 2004; Gregory 2005). Duplications play
12922-405: The double helix (from six-carbon ring to six-carbon ring) is called a Watson-Crick base pair. DNA with high GC-content is more stable than DNA with low GC -content. A Hoogsteen base pair (hydrogen bonding the 6-carbon ring to the 5-carbon ring) is a rare variation of base-pairing. As hydrogen bonds are not covalent , they can be broken and rejoined relatively easily. The two strands of DNA in
13064-442: The edges of the bases and chelation of a metal ion in the centre of each four-base unit. Other structures can also be formed, with the central set of four bases coming from either a single strand folded around the bases, or several different parallel strands, each contributing one base to the central structure. In addition to these stacked structures, telomeres also form large loop structures called telomere loops, or T-loops. Here,
13206-481: The end of an otherwise complementary double-strand of DNA. However, branched DNA can occur if a third strand of DNA is introduced and contains adjoining regions able to hybridize with the frayed regions of the pre-existing double-strand. Although the simplest example of branched DNA involves only three strands of DNA, complexes involving additional strands and multiple branches are also possible. Branched DNA can be used in nanotechnology to construct geometric shapes, see
13348-480: The envelope membrane is still unknown. The intracellular mature virions are then transported to the Golgi apparatus where it is wrapped with an additional two membranes, becoming the intracellular enveloped virus. This is transported along cytoskeletal microtubules to reach the cell periphery, where it fuses with the plasma membrane to become the cell-associated enveloped virus. This triggers actin tails on cell surfaces or
13490-441: The essential genetic material but they also contain smaller extrachromosomal plasmid molecules that carry important genetic information. The definition of 'genome' that is commonly used in the scientific literature is usually restricted to the large chromosomal DNA molecules in bacteria. Eukaryotic genomes are even more difficult to define because almost all eukaryotic species contain nuclear chromosomes plus extra DNA molecules in
13632-456: The fact that this virus is large and complex, replication is relatively quick taking approximately 12 hours until the host cell dies by the release of viruses. The replication of poxvirus is unusual for a virus with double-stranded DNA genome because it occurs in the cytoplasm, although this is typical of other large DNA viruses. Poxvirus encodes its own machinery for genome transcription, a DNA dependent RNA polymerase, which makes replication in
13774-599: The first end-to-end human genome sequence in March 2022. The term genome was created in 1920 by Hans Winkler , professor of botany at the University of Hamburg , Germany. The website Oxford Dictionaries and the Online Etymology Dictionary suggest the name is a blend of the words gene and chromosome . However, see omics for a more thorough discussion. A few related -ome words already existed, such as biome and rhizome , forming
13916-418: The focus is on the interactions between DNA and other molecules that mediate the function of the genome. Genomic DNA is tightly and orderly packed in the process called DNA condensation , to fit the small available volumes of the cell. In eukaryotes, DNA is located in the cell nucleus , with small amounts in mitochondria and chloroplasts . In prokaryotes, the DNA is held within an irregularly shaped body in
14058-461: The four major types of macromolecules that are essential for all known forms of life . The two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides . Each nucleotide is composed of one of four nitrogen-containing nucleobases ( cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose , and a phosphate group . The nucleotides are joined to one another in
14200-448: The functions of these RNAs are not entirely clear. One proposal is that antisense RNAs are involved in regulating gene expression through RNA-RNA base pairing. A few DNA sequences in prokaryotes and eukaryotes, and more in plasmids and viruses , blur the distinction between sense and antisense strands by having overlapping genes . In these cases, some DNA sequences do double duty, encoding one protein when read along one strand, and
14342-455: The genome has been replicated and encode the structural proteins to make the virus particle. The assembly of the virus particle occurs in five stages of maturation that lead to the final exocytosis of the new enveloped virion. After the genome has been replicated, the immature virion assembles the A5 protein to create the intracellular mature virion. The protein aligns and the brick-shaped envelope of
14484-458: The genome such as regulatory sequences (see non-coding DNA ), and often a substantial fraction of junk DNA with no evident function. Almost all eukaryotes have mitochondria and a small mitochondrial genome . Algae and plants also contain chloroplasts with a chloroplast genome. The study of the genome is called genomics . The genomes of many organisms have been sequenced and various regions have been annotated. The Human Genome Project
14626-406: The genomes of two organisms that are otherwise very distantly related. Horizontal gene transfer seems to be common among many microbes . Also, eukaryotic cells seem to have experienced a transfer of some genetic material from their chloroplast and mitochondrial genomes to their nuclear chromosomes. Recent empirical data suggest an important role of viruses and sub-viral RNA-networks to represent
14768-974: The headquarters of the federal Centers for Disease Control and Prevention (the C.D.C.) in Atlanta , Georgia (the United States) and at the Institute of Virus Preparations in Moscow. After the September 11 attacks in 2001, the American and UK governments have had increased concern over the use of smallpox, or a smallpox-like disease, in bioterrorism. However, several poxviruses including vaccinia virus, myxoma virus, tanapox virus and raccoon pox virus are currently being investigated for their therapeutic potential in various human cancers in preclinical and clinical studies. Poxviridae viral particles (virions) are generally enveloped (external enveloped virion), though
14910-448: The helical axis in a left-handed spiral, the opposite of the more common B form. These unusual structures can be recognized by specific Z-DNA binding proteins and may be involved in the regulation of transcription. For many years, exobiologists have proposed the existence of a shadow biosphere , a postulated microbial biosphere of Earth that uses radically different biochemical and molecular processes than currently known life. One of
15052-455: The human genome All the cells of an organism originate from a single cell, so they are expected to have identical genomes; however, in some cases, differences arise. Both the process of copying DNA during cell division and exposure to environmental mutagens can result in mutations in somatic cells. In some cases, such mutations lead to cancer because they cause cells to divide more quickly and invade surrounding tissues. In certain lymphocytes in
15194-425: The human genome and 9% of the fruit fly genome. Tandem repeats can be functional. For example, telomeres are composed of the tandem repeat TTAGGG in mammals, and they play an important role in protecting the ends of the chromosome. In other cases, expansions in the number of tandem repeats in exons or introns can cause disease . For example, the human gene huntingtin (Htt) typically contains 6–29 tandem repeats of
15336-517: The human immune system, V(D)J recombination generates different genomic sequences such that each cell produces a unique antibody or T cell receptors. During meiosis , diploid cells divide twice to produce haploid germ cells. During this process, recombination results in a reshuffling of the genetic material from homologous chromosomes so each gamete has a unique genome. Genome-wide reprogramming in mouse primordial germ cells involves epigenetic imprint erasure leading to totipotency . Reprogramming
15478-448: The hydration level, DNA sequence, the amount and direction of supercoiling, chemical modifications of the bases, the type and concentration of metal ions , and the presence of polyamines in solution. The first published reports of A-DNA X-ray diffraction patterns —and also B-DNA—used analyses based on Patterson functions that provided only a limited amount of structural information for oriented fibers of DNA. An alternative analysis
15620-427: The hydrolytic activities of cellular water, etc., also occur frequently. Although most of these damages are repaired, in any cell some DNA damage may remain despite the action of repair processes. These remaining DNA damages accumulate with age in mammalian postmitotic tissues. This accumulation appears to be an important underlying cause of aging. Many mutagens fit into the space between two adjacent base pairs, this
15762-412: The importance of 5-methylcytosine, it can deaminate to leave a thymine base, so methylated cytosines are particularly prone to mutations . Other base modifications include adenine methylation in bacteria, the presence of 5-hydroxymethylcytosine in the brain , and the glycosylation of uracil to produce the "J-base" in kinetoplastids . DNA can be damaged by many sorts of mutagens , which change
15904-418: The intracellular enveloped virion. These particles are then fused to the cell plasma to form the cell-associated enveloped virion, which encounters the microtubules and prepares to exit the cell as an extracellular enveloped virion. The assembly of the virus particle occurs in the cytoplasm of the cell and is a complex process that is currently being researched to understand each stage in more depth. Considering
16046-441: The minor groove is 12 Å (1.2 nm) in width. Due to the larger width of the major groove, the edges of the bases are more accessible in the major groove than in the minor groove. As a result, proteins such as transcription factors that can bind to specific sequences in double-stranded DNA usually make contact with the sides of the bases exposed in the major groove. This situation varies in unusual conformations of DNA within
16188-516: The mitochondrial genome (constituting up to 90% of the DNA of the cell). A DNA sequence is called a "sense" sequence if it is the same as that of a messenger RNA copy that is translated into protein. The sequence on the opposite strand is called the "antisense" sequence. Both sense and antisense sequences can exist on different parts of the same strand of DNA (i.e. both strands can contain both sense and antisense sequences). In both prokaryotes and eukaryotes, antisense RNA sequences are produced, but
16330-608: The more deadly smallpox, a worldwide effort to vaccinate everyone against smallpox began with the ultimate goal to rid the world of the plague-like epidemic. The last case of endemic smallpox occurred in Somalia in 1977. Extensive searches over two years detected no further cases, and in 1979 the World Health Organization (WHO) declared the disease officially eradicated. In 1986, all virus samples were destroyed or transferred to two approved WHO reference labs: at
16472-477: The most dangerous are double-strand breaks, as these are difficult to repair and can produce point mutations , insertions , deletions from the DNA sequence, and chromosomal translocations . These mutations can cause cancer . Because of inherent limits in the DNA repair mechanisms, if humans lived long enough, they would all eventually develop cancer. DNA damages that are naturally occurring , due to normal cellular processes that produce reactive oxygen species,
16614-476: The multicellular eukaryotic genomes. Much of this is due to the differing abundances of transposable elements, which evolve by creating new copies of themselves in the chromosomes. Eukaryote genomes often contain many thousands of copies of these elements, most of which have acquired mutations that make them defective. Here is a table of some significant or representative genomes. See #See also for lists of sequenced genomes. Initial sequencing and analysis of
16756-464: The new strand, and the cell ends up with a perfect copy of its DNA. Naked extracellular DNA (eDNA), most of it released by cell death, is nearly ubiquitous in the environment. Its concentration in soil may be as high as 2 μg/L, and its concentration in natural aquatic environments may be as high at 88 μg/L. Various possible functions have been proposed for eDNA: it may be involved in horizontal gene transfer ; it may provide nutrients; and it may act as
16898-795: The nucleotides CAG (encoding a polyglutamine tract). An expansion to over 36 repeats results in Huntington's disease , a neurodegenerative disease. Twenty human disorders are known to result from similar tandem repeat expansions in various genes. The mechanism by which proteins with expanded polygulatamine tracts cause death of neurons is not fully understood. One possibility is that the proteins fail to fold properly and avoid degradation, instead accumulating in aggregates that also sequester important transcription factors, thereby altering gene expression. Tandem repeats are usually caused by slippage during replication, unequal crossing-over and gene conversion. Transposable elements (TEs) are sequences of DNA with
17040-426: The nucleus but the 'genome' refers to only one copy of each chromosome. Some eukaryotes have distinctive sex chromosomes, such as the X and Y chromosomes of mammals, so the technical definition of the genome must include both copies of the sex chromosomes. For example, the standard reference genome of humans consists of one copy of each of the 22 autosomes plus one X chromosome and one Y chromosome. A genome sequence
17182-454: The open reading frame. In many species , only a small fraction of the total sequence of the genome encodes protein. For example, only about 1.5% of the human genome consists of protein-coding exons , with over 50% of human DNA consisting of non-coding repetitive sequences . The reasons for the presence of so much noncoding DNA in eukaryotic genomes and the extraordinary differences in genome size , or C-value , among species, represent
17324-428: The place of thymine in RNA and differs from thymine by lacking a methyl group on its ring. In addition to RNA and DNA, many artificial nucleic acid analogues have been created to study the properties of nucleic acids, or for use in biotechnology. Modified bases occur in DNA. The first of these recognized was 5-methylcytosine , which was found in the genome of Mycobacterium tuberculosis in 1925. The reason for
17466-530: The presence of these noncanonical bases in bacterial viruses ( bacteriophages ) is to avoid the restriction enzymes present in bacteria. This enzyme system acts at least in part as a molecular immune system protecting bacteria from infection by viruses. Modifications of the bases cytosine and adenine, the more common and modified DNA bases, play vital roles in the epigenetic control of gene expression in plants and animals. A number of noncanonical bases are known to occur in DNA. Most of these are modifications of
17608-412: The prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond . Therefore, any DNA strand normally has one end at which there is a phosphate group attached to the 5′ carbon of a ribose (the 5′ phosphoryl) and another end at which there is a free hydroxyl group attached to the 3′ carbon of a ribose (the 3′ hydroxyl). The orientation of
17750-590: The proportion of non-repetitive DNA decreases along with increasing genome size in complex eukaryotes. Noncoding sequences include introns , sequences for non-coding RNAs, regulatory regions, and repetitive DNA. Noncoding sequences make up 98% of the human genome. There are two categories of repetitive DNA in the genome: tandem repeats and interspersed repeats. Short, non-coding sequences that are repeated head-to-tail are called tandem repeats . Microsatellites consisting of 2–5 basepair repeats, while minisatellite repeats are 30–35 bp. Tandem repeats make up about 4% of
17892-466: The proposals was the existence of lifeforms that use arsenic instead of phosphorus in DNA . A report in 2010 of the possibility in the bacterium GFAJ-1 was announced, though the research was disputed, and evidence suggests the bacterium actively prevents the incorporation of arsenic into the DNA backbone and other biomolecules. At the ends of the linear chromosomes are specialized regions of DNA called telomeres . The main function of these regions
18034-439: The proteins encoded by LINEs for transposition. The Alu element is the most common SINE found in primates. It is about 350 base pairs and occupies about 11% of the human genome with around 1,500,000 copies. DNA transposons encode a transposase enzyme between inverted terminal repeats. When expressed, the transposase recognizes the terminal inverted repeats that flank the transposon and catalyzes its excision and reinsertion in
18176-444: The rate at 4–6 × 10. The last common ancestor of the extant poxviruses that infect vertebrates existed 0.5 million years ago . The genus Avipoxvirus diverged from the ancestor 249 ± 69 thousand years ago. The ancestor of the genus Orthopoxvirus was next to diverge from the other clades at 0.3 million years ago . A second estimate of this divergence time places this event at 166,000 ± 43,000 years ago. The division of
18318-432: The section on uses in technology below. Several artificial nucleobases have been synthesized, and successfully incorporated in the eight-base DNA analogue named Hachimoji DNA . Dubbed S, B, P, and Z, these artificial bases are capable of bonding with each other in a predictable way (S–B and P–Z), maintain the double helix structure of DNA, and be transcribed to RNA. Their existence could be seen as an indication that there
18460-431: The sequence of amino acids within proteins in a process called translation . Within eukaryotic cells, DNA is organized into long structures called chromosomes . Before typical cell division , these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms ( animals , plants , fungi and protists ) store most of their DNA inside
18602-476: The shape of a double helix . The nucleotide contains both a segment of the backbone of the molecule (which holds the chain together) and a nucleobase (which interacts with the other DNA strand in the helix). A nucleobase linked to a sugar is called a nucleoside , and a base linked to a sugar and to one or more phosphate groups is called a nucleotide . A biopolymer comprising multiple linked nucleotides (as in DNA)
18744-423: The shortest 45 000 000 nucleotides in length and the longest 248 000 000 nucleotides, each contained in a different chromosome. There is no clear and consistent correlation between morphological complexity and genome size in either prokaryotes or lower eukaryotes . Genome size is largely a function of the expansion and contraction of repetitive DNA elements. Since genomes are very complex, one research strategy
18886-552: The single-ringed pyrimidines and the double-ringed purines . In DNA, the pyrimidines are thymine and cytosine; the purines are adenine and guanine. Both strands of double-stranded DNA store the same biological information . This information is replicated when the two strands separate. A large part of DNA (more than 98% for humans) 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
19028-502: The single-stranded DNA curls around in a long circle stabilized by telomere-binding proteins. At the very end of the T-loop, the single-stranded telomere DNA is held onto a region of double-stranded DNA by the telomere strand disrupting the double-helical DNA and base pairing to one of the two strands. This triple-stranded structure is called a displacement loop or D-loop . In DNA, fraying occurs when non-complementary regions exist at
19170-518: The strands separate and exist in solution as two entirely independent molecules. These single-stranded DNA molecules have no single common shape, but some conformations are more stable than others. In humans, the total female diploid nuclear genome per cell extends for 6.37 Gigabase pairs (Gbp), is 208.23 cm long and weighs 6.51 picograms (pg). Male values are 6.27 Gbp, 205.00 cm, 6.41 pg. Each DNA polymer can contain hundreds of millions of nucleotides, such as in chromosome 1 . Chromosome 1
19312-474: The subfamily Chordopoxvirinae infect vertebrates and those in the subfamily Entomopoxvirinae infect insects . There are ten recognised genera in the Chordopoxvirinae and three in the Entomopoxvirinae . The following subfamilies and genera are recognized (- virinae denotes subfamily and - virus denotes genus): Chordopoxvirinae Entomopoxvirinae Both subfamilies also contain
19454-469: The sugar-phosphate to form the complete nucleotide, as shown for adenosine monophosphate . Adenine pairs with thymine and guanine pairs with cytosine, forming A-T and G-C base pairs . The nucleobases are classified into two types: the purines , A and G , which are fused five- and six-membered heterocyclic compounds , and the pyrimidines , the six-membered rings C and T . A fifth pyrimidine nucleobase, uracil ( U ), usually takes
19596-541: The virus), pol (reverse transcriptase and integrase), pro (protease), and in some cases env (envelope) genes. These genes are flanked by long repeats at both 5' and 3' ends. It has been reported that LTRs consist of the largest fraction in most plant genome and might account for the huge variation in genome size. Non-long terminal repeats (Non-LTRs) are classified as long interspersed nuclear elements (LINEs), short interspersed nuclear elements (SINEs), and Penelope-like elements (PLEs). In Dictyostelium discoideum , there
19738-405: Was extracted from the toe bone of a 130,000-year-old Neanderthal found in a Siberian cave . 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 full genome of James D. Watson , one of
19880-526: Was proposed by Wilkins et al. in 1953 for the in vivo B-DNA X-ray diffraction-scattering patterns of highly hydrated DNA fibers in terms of squares of Bessel functions . In the same journal, James Watson and Francis Crick presented their molecular modeling analysis of the DNA X-ray diffraction patterns to suggest that the structure was a double helix. Although the B-DNA form is most common under
20022-527: Was started in October 1990, and then reported the sequence of the human genome in April 2003, although the initial "finished" sequence was missing 8% of the genome consisting mostly of repetitive sequences. With advancements in technology that could handle sequencing of the many repetitive sequences found in human DNA that were not fully uncovered by the original Human Genome Project study, scientists reported
20164-502: Was thought to have been transferred to Europe around the early 8th century and then to the Americas in the early 16th century, resulting in the deaths of 3.2 million Aztecs within two years of introduction. This death toll can be attributed to the indigenous population's complete lack of exposure to the virus over millennia. A century after Edward Jenner showed that the less potent cowpox could be used to effectively vaccinate against
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