182-550: 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
364-459: A catalyst . Laboratory synthesis of biopolymers, especially of proteins , is an area of intensive research. There are three main classes of biopolymers: polysaccharides , polypeptides , and polynucleotides . In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase . The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from
546-441: A lower critical solution temperature phase transition (LCST), at which phase separation occurs with heating. In dilute solutions, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In
728-502: A bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent , or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer behaves like an ideal random coil . The transition between
910-441: 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
1092-461: 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
1274-450: 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,
1456-507: A circular mitochondrial genome. Medusozoa and calcarea clades however include species with linear mitochondrial chromosomes. With a few exceptions, animals have 37 genes in their mitochondrial DNA: 13 for proteins , 22 for tRNAs , and 2 for rRNAs . Mitochondrial genomes for animals average about 16,000 base pairs in length. The anemone Isarachnanthus nocturnus has the largest mitochondrial genome of any animal at 80,923 bp. The smallest known mitochondrial genome in animals belongs to
1638-445: 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
1820-593: A database) to determine maternal lineage. Most often, the comparison is made with the revised Cambridge Reference Sequence . Vilà et al. have published studies tracing the matrilineal descent of domestic dogs from wolves. The concept of the Mitochondrial Eve is based on the same type of analysis, attempting to discover the origin of humanity by tracking the lineage back in time. Entities subject to uniparental inheritance and with little to no recombination may be expected to be subject to Muller's ratchet ,
2002-408: A degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, crystallinity may also be associated with decreased transparency. The space occupied by a polymer molecule is generally expressed in terms of radius of gyration , which
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#17327581547962184-587: A deviation from a simple linear chain. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers , comb polymers , polymer brushes , dendronized polymers , ladder polymers , and dendrimers . There exist also two-dimensional polymers (2DP) which are composed of topologically planar repeat units. A polymer's architecture affects many of its physical properties including solution viscosity, melt viscosity, solubility in various solvents, glass-transition temperature and
2366-500: A donor female, and nuclear DNA from the mother and father. In the spindle transfer procedure, the nucleus of an egg is inserted into the cytoplasm of an egg from a donor female which has had its nucleus removed, but still contains the donor female's mtDNA. The composite egg is then fertilized with the male's sperm. The procedure is used when a woman with genetically defective mitochondria wishes to procreate and produce offspring with healthy mitochondria. The first known child to be born as
2548-490: 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
2730-435: A finding that has been rejected by other scientists. In sexual reproduction , mitochondria are normally inherited exclusively from the mother; the mitochondria in mammalian sperm are usually destroyed by the egg cell after fertilization. Also, mitochondria are present solely in the midpiece, which is used for propelling the sperm cells, and sometimes the midpiece, along with the tail, is lost during fertilization. In 1999 it
2912-464: A flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible. The attractive forces between polymer chains play a large part in determining the polymer's properties. Because polymer chains are so long, they have many such interchain interactions per molecule, amplifying the effect of these interactions on the polymer properties in comparison to attractions between conventional molecules. Different side groups on
3094-434: A genome suggests that complete gene loss is possible, and transferring mitochondrial genes to the nucleus has several advantages. The difficulty of targeting remotely-produced hydrophobic protein products to the mitochondrion is one hypothesis for why some genes are retained in mtDNA; colocalisation for redox regulation is another, citing the desirability of localised control over mitochondrial machinery. Recent analysis of
3276-479: A given application, the properties of a polymer can be tuned or enhanced by combination with other materials, as in composites . Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and lower use of fertilizers (synthetic fibres), preserve other materials (coatings), protect and save lives (hygiene, medical applications). A representative, non-exhaustive list of applications
3458-545: A healthy human sperm has been reported to contain on average 5 molecules), degradation of sperm mtDNA in the male genital tract and in the fertilized egg; and, at least in a few organisms, failure of sperm mtDNA to enter the egg. Whatever the mechanism, this single parent ( uniparental inheritance ) pattern of mtDNA inheritance is found in most animals, most plants and also in fungi. In a study published in 2018, human babies were reported to inherit mtDNA from both their fathers and their mothers resulting in mtDNA heteroplasmy ,
3640-439: 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
3822-402: A high surface quality and are also highly transparent so that the laser properties are dominated by the laser dye used to dope the polymer matrix. These type of lasers, that also belong to the class of organic lasers , are known to yield very narrow linewidths which is useful for spectroscopy and analytical applications. An important optical parameter in the polymer used in laser applications
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#17327581547964004-569: 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
4186-531: A larger change in conformation and adopt the Z form . Here, the strands turn about 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
4368-662: 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
4550-405: A mainstay of phylogenetics and evolutionary biology . It also permits tracing the relationships of populations, and so has become important in anthropology and biogeography . Nuclear and mitochondrial DNA are thought to have separate evolutionary origins, with the mtDNA derived from the circular genomes of bacteria engulfed by the ancestors of modern eukaryotic cells. This theory is called
4732-542: A mutation in mtDNA has been used to help diagnose prostate cancer in patients with negative prostate biopsy . mtDNA alterations can be detected in the bio-fluids of patients with cancer. mtDNA is characterized by the high rate of polymorphisms and mutations. Some of which are increasingly recognized as an important cause of human pathology such as oxidative phosphorylation (OXPHOS) disorders, maternally inherited diabetes and deafness (MIDD), Type 2 diabetes mellitus, Neurodegenerative disease , heart failure and cancer. Though
4914-626: A mutational (contrary to the selective one) explanation for the observation that long-lived species have GC-rich mtDNA: long-lived species become GC-rich simply because of their biased process of mutagenesis. An association between mtDNA mutational spectrum and species-specific life-history traits in mammals opens a possibility to link these factors together discovering new life-history-specific mutagens in different groups of organisms. Deletion breakpoints frequently occur within or near regions showing non-canonical (non-B) conformations, namely hairpins, cruciforms and cloverleaf-like elements. Moreover, there
5096-401: A polymer behaves as a continuous macroscopic material. They are classified as bulk properties, or intensive properties according to thermodynamics . The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale. The tensile strength of a material quantifies how much elongating stress
5278-421: A polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. A polymer which contains only a single type of repeat unit is known as a homopolymer , while a polymer containing two or more types of repeat units is known as a copolymer . A terpolymer is a copolymer which contains three types of repeat units. Polystyrene
5460-433: A polymeric material can be described at different length scales, from the sub-nm length scale up to the macroscopic one. There is in fact a hierarchy of structures, in which each stage provides the foundations for the next one. The starting point for the description of the structure of a polymer is the identity of its constituent monomers. Next, the microstructure essentially describes the arrangement of these monomers within
5642-536: A process called reptation in which each chain molecule is constrained by entanglements with neighboring chains to move within a virtual tube. The theory of reptation can explain polymer molecule dynamics and viscoelasticity . Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization and melting transitions , whereas amorphous polymers do not. In polymers, crystallization and melting do not suggest solid-liquid phase transitions, as in
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5824-436: 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
6006-525: A result of mitochondrial donation was a boy born to a Jordanian couple in Mexico on 6 April 2016. The concept that mtDNA is particularly susceptible to reactive oxygen species generated by the respiratory chain due to its proximity remains controversial. mtDNA does not accumulate any more oxidative base damage than nuclear DNA. It has been reported that at least some types of oxidative DNA damage are repaired more efficiently in mitochondria than they are in
6188-427: A result, they typically have lower melting temperatures than other polymers. When a polymer is dispersed or dissolved in a liquid, such as in commercial products like paints and glues, the chemical properties and molecular interactions influence how the solution flows and can even lead to self-assembly of the polymer into complex structures. When a polymer is applied as a coating, the chemical properties will influence
6370-510: A role in the mitochondrial bottleneck, exploiting cell-to-cell variability to ameliorate the inheritance of damaging mutations. According to Justin St. John and colleagues, "At the blastocyst stage, the onset of mtDNA replication is specific to the cells of the trophectoderm . In contrast, the cells of the inner cell mass restrict mtDNA replication until they receive the signals to differentiate to specific cell types." The two strands of
6552-516: 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 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
6734-443: 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
6916-435: A species and also for identifying and quantifying the phylogeny (evolutionary relationships; see phylogenetics ) among different species. To do this, biologists determine and then compare the mtDNA sequences from different individuals or species. Data from the comparisons is used to construct a network of relationships among the sequences, which provides an estimate of the relationships among the individuals or species from which
7098-630: A stabilisation or reduction in mutant load between generations. The mechanism underlying the bottleneck is debated, with a recent mathematical and experimental metastudy providing evidence for a combination of the random partitioning of mtDNAs at cell divisions and the random turnover of mtDNA molecules within the cell. Male mitochondrial DNA inheritance has been discovered in Plymouth Rock chickens . Evidence supports rare instances of male mitochondrial inheritance in some mammals as well. Specifically, documented occurrences exist for mice, where
7280-456: A statistical distribution of chain lengths, the molecular weight is expressed in terms of weighted averages. The number-average molecular weight ( M n ) and weight-average molecular weight ( M w ) are most commonly reported. The ratio of these two values ( M w / M n ) is the dispersity ( Đ ), which is commonly used to express the width of the molecular weight distribution. The physical properties of polymer strongly depend on
7462-537: A tendency to form amorphous and semicrystalline structures rather than crystals . Polymers are studied in the fields of polymer science (which includes polymer chemistry and polymer physics ), biophysics and materials science and engineering . Historically, products arising from the linkage of repeating units by covalent chemical bonds have been the primary focus of polymer science. An emerging important area now focuses on supramolecular polymers formed by non-covalent links. Polyisoprene of latex rubber
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7644-415: 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 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
7826-432: A variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of four types of nucleotide subunits. A polymer containing ionizable subunits (e.g., pendant carboxylic groups ) is known as a polyelectrolyte or ionomer , when the fraction of ionizable units is large or small respectively. The microstructure of a polymer (sometimes called configuration) relates to
8008-448: A wide range of mtDNA genomes suggests that both these features may dictate mitochondrial gene retention. Across all organisms, there are six main mitochondrial genome types, classified by structure (i.e. circular versus linear), size, presence of introns or plasmid like structures , and whether the genetic material is a singular molecule or collection of homogeneous or heterogeneous molecules. In many unicellular organisms (e.g.,
8190-405: A wide-meshed cross-linking between the "main chains". Close-meshed crosslinking, on the other hand, leads to thermosets . Cross-links and branches are shown as red dots in the figures. Highly branched polymers are amorphous and the molecules in the solid interact randomly. An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to
8372-814: Is a substance or material that consists of very large molecules, or macromolecules , that are constituted by many repeating subunits derived from one or more species of monomers . Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers . Their consequently large molecular mass , relative to small molecule compounds , produces unique physical properties including toughness , high elasticity , viscoelasticity , and
8554-479: Is a crucial physical parameter for polymer manufacturing, processing, and use. Below T g , molecular motions are frozen and polymers are brittle and glassy. Above T g , molecular motions are activated and polymers are rubbery and viscous. The glass-transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of plasticizers . Whereas crystallization and melting are first-order phase transitions ,
8736-532: Is a linear genome made up of homogeneous DNA molecules (type 5). Great variation in mtDNA gene content and size exists among fungi and plants, although there appears to be a core subset of genes present in all eukaryotes (except for the few that have no mitochondria at all). In Fungi, however, there is no single gene shared among all mitogenomes. Some plant species have enormous mitochondrial genomes, with Silene conica mtDNA containing as many as 11,300,000 base pairs. Surprisingly, even those huge mtDNAs contain
8918-410: Is a long-chain n -alkane. There are also branched macromolecules with a main chain and side chains, in the case of polyethylene the side chains would be alkyl groups . In particular unbranched macromolecules can be in the solid state semi-crystalline, crystalline chain sections highlighted red in the figure below. While branched and unbranched polymers are usually thermoplastics, many elastomers have
9100-467: Is a well-established marker of oxidative DNA damage. In persons with amyotrophic lateral sclerosis (ALS), the enzymes that normally repair 8-oxoG DNA damages in the mtDNA of spinal motor neurons are impaired. Thus oxidative damage to mtDNA of motor neurons may be a significant factor in the etiology of ALS. Over the past decade, an Israeli research group led by Professor Vadim Fraifeld has shown that strong and significant correlations exist between
9282-520: 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 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
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#17327581547969464-400: Is also commonly present in polymer backbones, such as those of polyethylene glycol , polysaccharides (in glycosidic bonds ), and DNA (in phosphodiester bonds ). Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This happens in
9646-512: Is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume , which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration. The simplest theoretical models for polymers in the molten, amorphous state are ideal chains . Polymer properties depend of their structure and they are divided into classes according to their physical bases. Many physical and chemical properties describe how
9828-481: Is an example of a natural polymer, and the polystyrene of styrofoam is an example of a synthetic polymer. In biological contexts, essentially all biological macromolecules —i.e., proteins (polyamides), nucleic acids (polynucleotides), and polysaccharides —are purely polymeric, or are composed in large part of polymeric components. The term "polymer" derives from Greek πολύς (polus) 'many, much' and μέρος (meros) 'part'. The term
10010-446: 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
10192-433: 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,
10374-428: Is composed only of styrene -based repeat units, and is classified as a homopolymer. Polyethylene terephthalate , even though produced from two different monomers ( ethylene glycol and terephthalic acid ), is usually regarded as a homopolymer because only one type of repeat unit is formed. Ethylene-vinyl acetate contains more than one variety of repeat unit and is a copolymer. Some biological polymers are composed of
10556-492: Is data supporting the involvement of helix-distorting intrinsically curved regions and long G-tetrads in eliciting instability events. In addition, higher breakpoint densities were consistently observed within GC-skewed regions and in the close vicinity of the degenerate sequence motif YMMYMNNMMHM. Unlike nuclear DNA, which is inherited from both parents and in which genes are rearranged in the process of recombination , there
10738-409: Is defined, for small strains , as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. Viscoelasticity describes a complex time-dependent elastic response, which will exhibit hysteresis in the stress-strain curve when
10920-433: 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
11102-425: Is found in plastids , such as chloroplasts . Human mitochondrial DNA was the first significant part of the human genome to be sequenced. This sequencing revealed that human mtDNA has 16,569 base pairs and encodes 13 proteins . As in other vertebrates, the human mitochondrial genetic code differs slightly from nuclear DNA. Since animal mtDNA evolves faster than nuclear genetic markers, it represents
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#173275815479611284-473: Is found in the blood of the mother, and can be sequenced to determine a great deal of information about the developing fetus. Polymer A polymer is a substance composed of macromolecules. A macromolecule is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. A polymer ( / ˈ p ɒ l ɪ m ər / )
11466-450: Is given below. Mitochondrial DNA Mitochondrial DNA ( mtDNA and mDNA ) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in a eukaryotic cell; most of the DNA is in the cell nucleus , and, in plants and algae, the DNA also
11648-411: 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
11830-419: 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
12012-514: Is observed in bivalve mollusks. In those species, females have only one type of mtDNA (F), whereas males have F type mtDNA in their somatic cells, but M type of mtDNA (which can be as much as 30% divergent) in germline cells. Paternally inherited mitochondria have additionally been reported in some insects such as fruit flies , honeybees , and periodical cicadas . An IVF technique known as mitochondrial donation or mitochondrial replacement therapy (MRT) results in offspring containing mtDNA from
12194-431: 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
12376-517: 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
12558-427: 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
12740-540: Is severely degraded. Autosomal cells only have two copies of nuclear DNA, but can have hundreds of copies of mtDNA due to the multiple mitochondria present in each cell. This means highly degraded evidence that would not be beneficial for STR analysis could be used in mtDNA analysis. mtDNA may be present in bones, teeth, or hair, which could be the only remains left in the case of severe degradation. In contrast to STR analysis, mtDNA sequencing uses Sanger sequencing . The known sequence and questioned sequence are both compared to
12922-410: 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 a second protein when read in
13104-435: Is the change in refractive index with temperature also known as dn/dT. For the polymers mentioned here the (dn/dT) ~ −1.4 × 10 in units of K in the 297 ≤ T ≤ 337 K range. Most conventional polymers such as polyethylene are electrical insulators , but the development of polymers containing π-conjugated bonds has led to a wealth of polymer-based semiconductors , such as polythiophenes . This has led to many applications in
13286-485: Is the first multicellular organism known to have this absence of aerobic respiration and live completely free of oxygen dependency. There are three different mitochondrial genome types in plants and fungi. The first type is a circular genome that has introns (type 2) and may range from 19 to 1000 kbp in length. The second genome type is a circular genome (about 20–1000 kbp) that also has a plasmid-like structure (1 kb) (type 3). The final genome type found in plants and fungi
13468-563: Is the main constituent of wood and paper. Hemoglycin (previously termed hemolithin ) is a space polymer that is the first polymer of amino acids found in meteorites . The list of synthetic polymers , roughly in order of worldwide demand, includes polyethylene , polypropylene , polystyrene , polyvinyl chloride , synthetic rubber , phenol formaldehyde resin (or Bakelite ), neoprene , nylon , polyacrylonitrile , PVB , silicone , and many more. More than 330 million tons of these polymers are made every year (2015). Most commonly,
13650-439: 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
13832-400: 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 the functions of these RNAs are not entirely clear. One proposal
14014-452: Is used in an analogous way to determine the patrilineal history.) This is usually accomplished on human mitochondrial DNA by sequencing the hypervariable control regions (HVR1 or HVR2), and sometimes the complete molecule of the mitochondrial DNA, as a genealogical DNA test . HVR1, for example, consists of about 440 base pairs. These 440 base pairs are compared to the same regions of other individuals (either specific people or subjects in
14196-510: Is usually no change in mtDNA from parent to offspring. Although mtDNA also recombines, it does so with copies of itself within the same mitochondrion. Because of this and because the mutation rate of animal mtDNA is higher than that of nuclear DNA, mtDNA is a powerful tool for tracking ancestry through females ( matrilineage ) and has been used in this role to track the ancestry of many species back hundreds of generations. mtDNA testing can be used by forensic scientists in cases where nuclear DNA
14378-521: The POLG2 gene. The replisome machinery is formed by DNA polymerase, TWINKLE and mitochondrial SSB proteins . TWINKLE is a helicase , which unwinds short stretches of dsDNA in the 5' to 3' direction. All these polypeptides are encoded in the nuclear genome. During embryogenesis , replication of mtDNA is strictly down-regulated from the fertilized oocyte through the preimplantation embryo. The resulting reduction in per-cell copy number of mtDNA plays
14560-654: 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,
14742-406: 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
14924-468: 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
15106-518: The ciliate Tetrahymena and the green alga Chlamydomonas reinhardtii ), and in rare cases also in multicellular organisms (e.g. in some species of Cnidaria ), the mtDNA is linear DNA . Most of these linear mtDNAs possess telomerase -independent telomeres (i.e., the ends of the linear DNA ) with different modes of replication, which have made them interesting objects of research because many of these unicellular organisms with linear mtDNA are known pathogens . Most ( bilaterian ) animals have
15288-499: The endosymbiotic theory . In the cells of extant organisms, the vast majority of the proteins in the mitochondria (numbering approximately 1500 different types in mammals ) are coded by nuclear DNA , but the genes for some, if not most, of them are thought to be of bacterial origin, having been transferred to the eukaryotic nucleus during evolution . The reasons mitochondria have retained some genes are debated. The existence in some species of mitochondrion-derived organelles lacking
15470-419: 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
15652-589: 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
15834-432: 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
16016-671: 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, 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,
16198-470: 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 is introduced by enzymes called topoisomerases . These enzymes are also needed to relieve
16380-496: The DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids . The protein may be modified further following translation in order to provide appropriate structure and functioning. There are other biopolymers such as rubber , suberin , melanin , and lignin . Naturally occurring polymers such as cotton , starch , and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on
16562-400: 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
16744-572: The Revised Cambridge Reference Sequence to generate their respective haplotypes. If the known sample sequence and questioned sequence originated from the same matriline, one would expect to see identical sequences and identical differences from the rCRS. Cases arise where there are no known samples to collect and the unknown sequence can be searched in a database such as EMPOP. The Scientific Working Group on DNA Analysis Methods recommends three conclusions for describing
16926-491: 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
17108-543: The accumulation of deleterious mutations until functionality is lost. Animal populations of mitochondria avoid this through a developmental process known as the mtDNA bottleneck . The bottleneck exploits random processes in the cell to increase the cell-to-cell variability in mutant load as an organism develops: a single egg cell with some proportion of mutant mtDNA thus produces an embryo in which different cells have different mutant loads. Cell-level selection may then act to remove those cells with more mutant mtDNA, leading to
17290-419: The accumulation of mtDNA damage in several organs of rats. For example, dietary restriction prevented age-related accumulation of mtDNA damage in the cortex and decreased it in the lung and testis. Increased mt DNA damage is a feature of several neurodegenerative diseases . The brains of individuals with Alzheimer's disease have elevated levels of oxidative DNA damage in both nuclear DNA and mtDNA, but
17472-441: The adhesion of the coating and how it interacts with external materials, such as superhydrophobic polymer coatings leading to water resistance. Overall the chemical properties of a polymer are important elements for designing new polymeric material products. Polymers such as PMMA and HEMA:MMA are used as matrices in the gain medium of solid-state dye lasers , also known as solid-state dye-doped polymer lasers. These polymers have
17654-434: The backbone in a variety of ways. A copolymer containing a controlled arrangement of monomers is called a sequence-controlled polymer . Alternating, periodic and block copolymers are simple examples of sequence-controlled polymers . Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types of tacticity: isotactic (all substituents on
17836-523: 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 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
18018-407: 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
18200-464: 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
18382-421: The case of water or other molecular fluids. Instead, crystallization and melting refer to the phase transitions between two solid states ( i.e. , semi-crystalline and amorphous). Crystallization occurs above the glass-transition temperature ( T g ) and below the melting temperature ( T m ). All polymers (amorphous or semi-crystalline) go through glass transitions . The glass-transition temperature ( T g )
18564-581: 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
18746-616: 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
18928-456: The coding instructions for some proteins, which may have an effect on organism metabolism and/or fitness. Mutations of mitochondrial DNA can lead to a number of illnesses including exercise intolerance and Kearns–Sayre syndrome (KSS), which causes a person to lose full function of heart, eye, and muscle movements. Some evidence suggests that they might be major contributors to the aging process and age-associated pathologies . Particularly in
19110-434: The comb jelly Vallicula multiformis , which consist of 9,961 bp. In February 2020, a jellyfish-related parasite – Henneguya salminicola – was discovered that lacks a mitochondrial genome but retains structures deemed mitochondrion-related organelles. Moreover, nuclear DNA genes involved in aerobic respiration and in mitochondrial DNA replication and transcription were either absent or present only as pseudogenes . This
19292-718: The context of disease, the proportion of mutant mtDNA molecules in a cell is termed heteroplasmy . The within-cell and between-cell distributions of heteroplasmy dictate the onset and severity of disease and are influenced by complicated stochastic processes within the cell and during development. Mutations in mitochondrial tRNAs can be responsible for severe diseases like the MELAS and MERRF syndromes. Mutations in nuclear genes that encode proteins that mitochondria use can also contribute to mitochondrial diseases. These diseases do not follow mitochondrial inheritance patterns, but instead follow Mendelian inheritance patterns. Recently
19474-476: The continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene ('polythene' in British English), whose repeat unit or monomer is ethylene . Many other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen
19656-404: 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
19838-448: 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
20020-536: The degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers. Polymers with
20202-403: The differences between a known mtDNA sequence and a questioned mtDNA sequence: exclusion for two or more differences between the sequences, inconclusive if there is one nucleotide difference, or cannot exclude if there are no nucleotide differences between the two sequences. The rapid mutation rate (in animals) makes mtDNA useful for assessing genetic relationships of individuals or groups within
20384-626: The differences in animal species maximum life spans in a multiplicative manner (i.e., species maximum life span = their mtDNA GC% * metabolic rate). To support the scientific community in carrying out comparative analyses between mtDNA features and longevity across animals, a dedicated database was built named MitoAge . De novo mutations arise either due to mistakes during DNA replication or due to unrepaired damage caused in turn by endogenous and exogenous mutagens. It has been long believed that mtDNA can be particularly sensitive to damage caused by reactive oxygen species (ROS), however G>T substitutions,
20566-404: 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
20748-400: The driving force for mixing is usually entropy , not interaction energy. In other words, miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction, but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with
20930-441: 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,
21112-480: 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
21294-417: The field of organic electronics . Nowadays, synthetic polymers are used in almost all walks of life. Modern society would look very different without them. The spreading of polymer use is connected to their unique properties: low density, low cost, good thermal/electrical insulation properties, high resistance to corrosion, low-energy demanding polymer manufacture and facile processing into final products. For
21476-418: 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
21658-459: 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
21840-527: The free energy of mixing for polymer solutions and thereby making solvation less favorable, and thereby making the availability of concentrated solutions of polymers far rarer than those of small molecules. Furthermore, the phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition (UCST), at which phase separation occurs with cooling, polymer mixtures commonly exhibit
22022-403: The genetic distances of distantly related species. Statistical models that treat substitution rates among codon positions separately, can thus be used to simultaneously estimate phylogenies that contain both closely and distantly related species Mitochondrial DNA was admitted into evidence for the first time ever in a United States courtroom in 1996 during State of Tennessee v. Paul Ware . In
22204-401: The glass transition is not. The glass transition shares features of second-order phase transitions (such as discontinuity in the heat capacity, as shown in the figure), but it is generally not considered a thermodynamic transition between equilibrium states. In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results from the fact that
22386-477: The hallmark of the oxidative damage in the nuclear genome, are very rare in mtDNA and do not increase with age. Comparing the mtDNA mutational spectra of hundreds of mammalian species, it has been recently demonstrated that species with extended lifespans have an increased rate of A>G substitutions on single-stranded heavy chain. This discovery led to the hypothesis that A>G is a mitochondria-specific marker of age-associated oxidative damage. This finding provides
22568-421: The human mitochondrial DNA are distinguished as the heavy strand and the light strand. The heavy strand is rich in guanine and encodes 12 subunits of the oxidative phosphorylation system, two ribosomal RNAs (12S and 16S), and 14 transfer RNAs (tRNAs). The light strand encodes one subunit, and 8 tRNAs. So, altogether mtDNA encodes for two rRNAs, 22 tRNAs, and 13 protein subunits , all of which are involved in
22750-424: 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
22932-524: The idea is controversial, some evidence suggests a link between aging and mitochondrial genome dysfunction. In essence, mutations in mtDNA upset a careful balance of reactive oxygen species (ROS) production and enzymatic ROS scavenging (by enzymes like superoxide dismutase , catalase , glutathione peroxidase and others). However, some mutations that increase ROS production (e.g., by reducing antioxidant defenses) in worms increase, rather than decrease, their longevity. Also, naked mole rats , rodents about
23114-408: 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
23296-415: The individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures. Copolymers are classified either as statistical copolymers, alternating copolymers, block copolymers, graft copolymers or gradient copolymers. In the schematic figure below, Ⓐ and Ⓑ symbolize the two repeat units . Monomers within a copolymer may be organized along
23478-466: The initiation of the transcription of the heavy and light strands are located in the main non-coding region of the mtDNA called the displacement loop, the D-loop . There is evidence that the transcription of the mitochondrial rRNAs is regulated by the heavy-strand promoter 1 (HSP1), and the transcription of the polycistronic transcripts coding for the protein subunits are regulated by HSP2. Measurement of
23660-451: The latter case, increasing the polymer chain length 10-fold would increase the viscosity over 1000 times. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass-transition temperature (T g ). This is a result of the increase in chain interactions such as van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix
23842-436: The length (or equivalently, the molecular weight) of the polymer chain. One important example of the physical consequences of the molecular weight is the scaling of the viscosity (resistance to flow) in the melt. The influence of the weight-average molecular weight ( M w {\displaystyle M_{w}} ) on the melt viscosity ( η {\displaystyle \eta } ) depends on whether
24024-415: The levels of the mtDNA-encoded RNAs in bovine tissues has shown that there are major differences in the expression of the mitochondrial RNAs relative to total tissue RNA. Among the 12 tissues examined the highest level of expression was observed in heart, followed by brain and steroidogenic tissue samples. As demonstrated by the effect of the trophic hormone ACTH on adrenal cortex cells, the expression of
24206-417: The load is removed. Dynamic mechanical analysis or DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time. Transport properties such as diffusivity describe how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes. The movement of individual macromolecules occurs by
24388-443: The longevity of species. The application of a mitochondrial-specific ROS scavenger, which lead to a significant longevity of the mice studied, suggests that mitochondria may still be well-implicated in ageing. Extensive research is being conducted to further investigate this link and methods to combat ageing. Presently, gene therapy and nutraceutical supplementation are popular areas of ongoing research. Bjelakovic et al. analyzed
24570-424: The male-inherited mitochondria were subsequently rejected. It has also been found in sheep, and in cloned cattle. Rare cases of male mitochondrial inheritance have been documented in humans. Although many of these cases involve cloned embryos or subsequent rejection of the paternal mitochondria, others document in vivo inheritance and persistence under lab conditions. Doubly uniparental inheritance of mtDNA
24752-436: The market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur . Ways in which polymers can be modified include oxidation , cross-linking , and end-capping . The structure of
24934-413: The material will endure before failure. This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general, tensile strength increases with polymer chain length and crosslinking of polymer chains. Young's modulus quantifies the elasticity of the polymer. It
25116-439: 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
25298-525: The mitochondrial genes may be strongly regulated by external factors, apparently to enhance the synthesis of mitochondrial proteins necessary for energy production. Interestingly, while the expression of protein-encoding genes was stimulated by ACTH, the levels of the mitochondrial 16S rRNA showed no significant change. In most multicellular organisms , mtDNA is inherited from the mother (maternally inherited). Mechanisms for this include simple dilution (an egg contains on average 200,000 mtDNA molecules, whereas
25480-474: 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,
25662-480: The mtDNA base composition and animal species-specific maximum life spans. As demonstrated in their work, higher mtDNA guanine + cytosine content ( GC% ) strongly associates with longer maximum life spans across animal species. An additional observation is that the mtDNA GC% correlation with the maximum life spans is independent of the well-known correlation between animal species metabolic rate and maximum life spans. The mtDNA GC% and resting metabolic rate explain
25844-838: The mtDNA has approximately 10-fold higher levels than nuclear DNA. It has been proposed that aged mitochondria is the critical factor in the origin of neurodegeneration in Alzheimer's disease. Analysis of the brains of AD patients suggested an impaired function of the DNA repair pathway, which would cause reduce the overall quality of mtDNA. In Huntington's disease , mutant huntingtin protein causes mitochondrial dysfunction involving inhibition of mitochondrial electron transport , higher levels of reactive oxygen species and increased oxidative stress . Mutant huntingtin protein promotes oxidative damage to mtDNA, as well as nuclear DNA, that may contribute to Huntington's disease pathology . The DNA oxidation product 8-oxoguanine (8-oxoG)
26026-558: The mtDNAs were taken. mtDNA can be used to estimate the relationship between both closely related and distantly related species. Due to the high mutation rate of mtDNA in animals, the 3rd positions of the codons change relatively rapidly, and thus provide information about the genetic distances among closely related individuals or species. On the other hand, the substitution rate of mt-proteins is very low, thus amino acid changes accumulate slowly (with corresponding slow changes at 1st and 2nd codon positions) and thus they provide information about
26208-461: 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
26390-472: The nucleus. mtDNA is packaged with proteins which appear to be as protective as proteins of the nuclear chromatin. Moreover, mitochondria evolved a unique mechanism which maintains mtDNA integrity through degradation of excessively damaged genomes followed by replication of intact/repaired mtDNA. This mechanism is not present in the nucleus and is enabled by multiple copies of mtDNA present in mitochondria. The outcome of mutation in mtDNA may be an alteration in
26572-444: The number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture is far smaller than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, is comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase
26754-453: 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
26936-448: 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 the axis of the double helix once every 10.4 base pairs, but if
27118-487: The oxidative phosphorylation process. Between most (but not all) protein-coding regions, tRNAs are present (see the human mitochondrial genome map ). During transcription, the tRNAs acquire their characteristic L-shape that gets recognized and cleaved by specific enzymes. With the mitochondrial RNA processing, individual mRNA, rRNA, and tRNA sequences are released from the primary transcript. Folded tRNAs therefore act as secondary structure punctuations. The promoters for
27300-719: The partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than Kevlar 's ( Twaron ), but polyesters have greater flexibility. Polymers with non-polar units such as polyethylene interact only through weak Van der Waals forces . As
27482-422: The physical arrangement of monomer residues along the backbone of the chain. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Various polymer structures can be produced depending on the monomers and reaction conditions: A polymer may consist of linear macromolecules containing each only one unbranched chain. In the case of unbranched polyethylene, this chain
27664-426: 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
27846-466: The plant and fungal genomes also exist in some protists, as do two unique genome types. One of these unique types is a heterogeneous collection of circular DNA molecules (type 4) while the other is a heterogeneous collection of linear molecules (type 6). Genome types 4 and 6 each range from 1–200 kbp in size. The smallest mitochondrial genome sequenced to date is the 5,967 bp mtDNA of the parasite Plasmodium falciparum . Endosymbiotic gene transfer,
28028-399: The polymer and create gaps between polymer chains for greater mobility and fewer interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used in clothing for
28210-426: The polymer at the scale of a single chain. The microstructure determines the possibility for the polymer to form phases with different arrangements, for example through crystallization , the glass transition or microphase separation . These features play a major role in determining the physical and chemical properties of a polymer. The identity of the repeat units (monomer residues, also known as "mers") comprising
28392-543: The polymer can lend the polymer to ionic bonding or hydrogen bonding between its own chains. These stronger forces typically result in higher tensile strength and higher crystalline melting points. The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to
28574-403: The polymer is above or below the onset of entanglements . Below the entanglement molecular weight , η ∼ M w 1 {\displaystyle \eta \sim {M_{w}}^{1}} , whereas above the entanglement molecular weight, η ∼ M w 3.4 {\displaystyle \eta \sim {M_{w}}^{3.4}} . In
28756-583: The polymerization of PET polyester . The monomers are terephthalic acid (HOOC—C 6 H 4 —COOH) and ethylene glycol (HO—CH 2 —CH 2 —OH) but the repeating unit is —OC—C 6 H 4 —COO—CH 2 —CH 2 —O—, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Synthetic methods are generally divided into two categories, step-growth polymerization and chain polymerization . The essential difference between
28938-527: 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
29120-411: 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
29302-499: The process by which genes that were coded in the mitochondrial genome are transferred to the cell's main genome, likely explains why more complex organisms such as humans have smaller mitochondrial genomes than simpler organisms such as protists. Mitochondrial DNA is replicated by the DNA polymerase gamma complex which is composed of a 140 kDa catalytic DNA polymerase encoded by the POLG gene and two 55 kDa accessory subunits encoded by
29484-461: 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
29666-409: The results of 78 studies between 1977 and 2012, involving a total of 296,707 participants, and concluded that antioxidant supplements do not reduce all-cause mortality nor extend lifespan, while some of them, such as beta carotene, vitamin E, and higher doses of vitamin A, may actually increase mortality. In a recent study, it was shown that dietary restriction can reverse ageing alterations by affecting
29848-626: 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 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
30030-442: The same number and kinds of genes as related plants with much smaller mtDNAs. The genome of the mitochondrion of the cucumber ( Cucumis sativus ) consists of three circular chromosomes (lengths 1556, 84 and 45 kilobases), which are entirely or largely autonomous with regard to their replication . Protists contain the most diverse mitochondrial genomes, with five different types found in this kingdom. Type 2, type 3 and type 5 of
30212-437: The same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents). Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. The macroscopic physical properties of a polymer are related to the interactions between the polymer chains. When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases,
30394-432: 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
30576-431: 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
30758-476: 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)
30940-552: 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
31122-500: 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
31304-500: The size of mice , live about eight times longer than mice despite having reduced, compared to mice, antioxidant defenses and increased oxidative damage to biomolecules. Once, there was thought to be a positive feedback loop at work (a 'Vicious Cycle'); as mitochondrial DNA accumulates genetic damage caused by free radicals, the mitochondria lose function and leak free radicals into the cytosol . A decrease in mitochondrial function reduces overall metabolic efficiency. However, this concept
31486-512: The size of individual polymer coils in solution. A variety of techniques may be employed for the synthesis of a polymeric material with a range of architectures, for example living polymerization . A common means of expressing the length of a chain is the degree of polymerization , which quantifies the number of monomers incorporated into the chain. As with other molecules, a polymer's size may also be expressed in terms of molecular weight . Since synthetic polymerization techniques typically yield
31668-448: The states is known as a coil–globule transition . Inclusion of plasticizers tends to lower T g and increase polymer flexibility. Addition of the plasticizer will also modify dependence of the glass-transition temperature T g on the cooling rate. The mobility of the chain can further change if the molecules of plasticizer give rise to hydrogen bonding formation. Plasticizers are generally small molecules that are chemically similar to
31850-466: 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
32032-686: The term crystalline finds identical usage to that used in conventional crystallography . For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography , may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions;
32214-485: 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 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
32396-439: 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 the hydration level, DNA sequence, the amount and direction of supercoiling, chemical modifications of
32578-555: The two is that in chain polymerization, monomers are added to the chain one at a time only, such as in polystyrene , whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester . Step-growth polymerization can be divided into polycondensation , in which low-molar-mass by-product is formed in every reaction step, and polyaddition . Newer methods, such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without
32760-605: Was coined in 1833 by Jöns Jacob Berzelius , though with a definition distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger , who spent the next decade finding experimental evidence for this hypothesis. Polymers are of two types: naturally occurring and synthetic or man made . Natural polymeric materials such as hemp , shellac , amber , wool , silk , and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose , which
32942-410: Was conclusively disproved when it was demonstrated that mice, which were genetically altered to accumulate mtDNA mutations at accelerated rate do age prematurely, but their tissues do not produce more ROS as predicted by the 'Vicious Cycle' hypothesis. Supporting a link between longevity and mitochondrial DNA, some studies have found correlations between biochemical properties of the mitochondrial DNA and
33124-460: Was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin to select them for later destruction inside the embryo . Some in vitro fertilization techniques, particularly injecting a sperm into an oocyte , may interfere with this. The fact that mitochondrial DNA is mostly maternally inherited enables genealogical researchers to trace maternal lineage far back in time. ( Y-chromosomal DNA , paternally inherited,
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