deoxyribonucleic acid

The type of nucleic acid containing deoxyribose as the sugar component and found principally in the nuclei (chromatin, chromosomes) and mitochondria of animal and plant cells, usually loosely bound to protein (hence the term deoxyribonucleoprotein); considered to be the autoreproducing component of chromosomes and of many viruses, and the repository of hereditary characteristics. Its linear macromolecular chain consists of deoxyribose molecules esterified with phosphate groups between the 3′- and 5′-hydroxyl groups; linked to this structure are the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C) and thymine (T). DNA may be open-ended or circular, single- or double-stranded, and many forms are known, the most commonly described of which is double-stranded, wherein the pyrimidines and purines cross-link through hydrogen bonding in the schema A-T and C-G, bringing two antiparallel strands into a double helix. Chromosomes are composed of double-stranded DNA; mitochondrial DNA is circular.

- A-DNA a form of DNA in which the helix is right-handed and the overall appearance is short and broad.

- antisense DNA the strand of DNA complementary to the one bearing the genetic message and from which it may be reconstructed. A DNA sequence complementary to a portion of mRNA. Used as potential therapeutic to stop transcription or translation of pathogens or inappropriately expressed host gene.

- B-DNA a form of DNA in which the helix is right-handed and the overall appearance is long and thin.

- blunt-ended DNA double-stranded DNA in which at least one of the ends has no unpaired bases.

- competitor DNA dNA from a test organism that is denatured and then used in in vitro hybridization experiments in which it competes with DNA (homologous) from a reference organism; used to determine the relationship of the test organism to the reference organism.

- complementary DNA (cDNA) 1. single-stranded DNA that is complementary to messenger RNA; 2. dNA that has been synthesized from mRNA by the action of reverse transcriptase.

- extrachromosomal DNA dNA that occurs naturally outside of the nucleus ( e.g., mitochondrial DNA).

- DNA fingerprinting a technique used to compare individuals by molecular genotyping. DNA isolated from a biological specimen is digested and fractionated. Southern hybridization with a radiolabeled repetitive DNA provides an autoradiographic pattern unique to the individual. SYN: DNA profiling, DNA typing.A technique developed in 1985 for comparing sets of DNA by locating identical sequences of nucleotides. Forensic applications of DNA fingerprinting are based on the premise that no 2 persons have exactly the same genetic makeup. The most distinctive features of an individual's genome are not the genes themselves but the variable number of tandem repeats (VNTRs) that occur between genes. While these do not transmit genetic information, they are highly consistent within the cells of an individual and highly variable from one individual to another. In DNA fingerprinting, the specimen is split into nucleotide fragments by treatment with restriction enzymes and then subjected to gel electrophoresis so as to yield a characteristic pattern of banding. Radioactive probes, composed of short nucleotide sequences (10–15 base pairs), then identify sites of tandem repeats and hybridize with them. Comparing the results from 2 or more DNA sources reveals their degree of relatedness. DNA fingerprinting offers a statistical basis for evaluating the probability that samples of blood, hair, semen, or tissue have originated from a given person. It also offers a means of determining lineages of humans and animals. The U.S. National Academy of Sciences has cautiously endorsed the use of DNA fingerprints as criminal evidence, while calling for further research and standardization of the technique.

- genomic DNA dNA that contains both introns and exons.

- junk DNA selfish DNA; that portion of DNA that is not transcribed and expressed, comprising a major fraction of the base pairs of the human genome; its function is not known.

- DNA ligase an enzyme that leads to the formation of a phosphodiester bond at a break of one strand in duplex DNA; a part of the DNA repair system.

- linker DNA the DNA found between nucleosomes on chromatin; since it is not complexed to proteins as strongly as other forms of DNA, it is accessible to exonuclease hydrolysis.

- DNA nucleotidylexotransferase an enzyme that can catalyze the addition of a nucleotide, presented as a nucleoside triphosphate, on a DNA or similar polydeoxynucleotide; has been used in DNA recombination studies to add nucleotides to form homopolymer tails. SYN: terminal addition enzyme, terminal deoxynucleotidyltransferase.

- palindromic DNA a segment of DNA in which the sequence is symmetrical about its midpoint.

- DNA polymerase nucleotidyltransferases.

- DNA profiling SYN: DNA fingerprinting.

- recombinant DNA altered DNA resulting from the insertion into the chain, by chemical, enzymatic, or biologic means, of a sequence (a whole or partial chain of DNA) not originally (biologically) present in that chain.

- repetitive DNA a segment of DNA that consists of a linear array of multiple copies of the same sequence of nucleotides.

- satellite DNA dNA in the satellite regions of acrocentric chromosomes.

- sticky-ended DNA double-stranded DNA in which one of the strands protrudes from the other strand ( I.E., has a number of unpaired bases) at one end or more.

- DNA typing SYN: DNA fingerprinting.

- Z-DNA a form of DNA in which the helix is left-handed, and the overall appearance is elongated and slim.

- zero time-binding DNA DNA that has become the duplex form at the start of a reassociation process.

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de·oxy·ri·bo·nu·cle·ic acid (')dē-'äk-si-.rī-bō-n(y)u̇-.klē-ik-, -.klā- also des·oxy·ri·bo·nu·cle·ic acid (')des- n DNA

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see DNA

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(DNA) de·oxy·ri·bo·nu·cle·ic ac·id (DNA) (de-ok″se-ri″bo-noo-kleґik) the nucleic acid in which the sugar is deoxyribose, constituting the primary genetic material of all cellular organisms and the DNA viruses, and occurring predominantly in the nucleus. It is a linear or circular polymer with a backbone composed of deoxyribose moieties that are linked by phosphate groups attached to their 5′ and 3′ hydroxyls, with side chains composed of purine (adenine, guanine) and pyrimidine (cytosine, thymine) bases attached to the sugars. In double-stranded DNA (see illustration), the strands are twisted to form a double helix (q.v.) and are antiparallel. Adenine forms two hydrogen bonds with thymine, and cytosine forms three with guanine; these are complementary base pairs and thus each chain contains information completely specifying the other. The complementary base pairing provides the mechanism for DNA to duplicate itself by replication and also to serve as a template for synthesis of ribonucleic acid (transcription). For specific types of DNA, see under DNA.

The DNA double helix. A, Diagrammatic model of the helical structure, showing its dimensions, the major and minor grooves, the periodicity of the bases, and the antiparallel orientation of the backbone chains (represented by ribbons). The base pairs (represented by rods) are perpendicular to the axis and lie stacked one on another. B, The chemical structure of the backbone and bases of DNA, showing the sugar phosphate linkages of the backbone and the hydrogen bonding between the base pairs. There are two hydrogen bonds between adenine and thymine, and three between cytosine and guanine.