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DNA[Abbr. of deoxyribonucleic acid]
A complex nucleic acid of high molecular weight consisting of nucleotides made of deoxyribose, phosphoric acid, and one of four bases (two purines, adenine [A] and guanine [G], and two pyrimidines, thymine [T] and cytosine [C]). The nucleotides are arranged in a double helix (two long spirals twisting around each other) joined by hydrogen bonds between the complementary base pairs A-T and C-G. Nucleic acid, present in chromosomes of the nuclei of cells, is the chemical basis of heredity and the carrier of genetic information for all organisms except the RNA viruses. See: chromosome; gene; RNA; virus
A double-stranded copy of a single-stranded RNA molecule, made by reverse transcriptase, an enzyme used by retroviruses such as HIV-1.
covalently closed circular DNAAbbreviation: cccDNA
Traces of nucleic acids found in the stool of people with colorectal cancers and polyps. Detection of DNA in stool has been proposed as an alternative to testing samples of stool for occult blood loss. Testing stool for traces of malignant DNA is a more sensitive screening test for intestinal cancer than screening stool samples for occult blood, but the test is expensive and is not as accurate a screening tool as colonoscopy.Synonym: stool DNA testing
mitochondrial DNAAbbreviation: mtDNA
DNA found in mitochondria. It differs from nuclear DNA in its nucleotide sequences, its size (about 16.5 kb), and its source (it is derived solely from the egg, not the sperm). Variations in mtDNA point to the ways in which members of a related population differ from each other genetically.
DNA that has been modified to remove the proteins that normally surround it. It is used for genetic transfers and vaccine manufacture.
Segments of DNA from one organism artificially manipulated or inserted into the DNA of another organism through gene splicing. When the host's genetic material is reproduced, the transplanted genetic material is also copied. Gene splicing permits isolation and examination of the properties and action of specific genes. See: plasmid; gene splicing
spacer DNASpacer sequence. See: Structure of DNA
spacer sequence, spacer DNA
The genetic material on a chromosome that separates actively transcribed genes. It may make up the largest part of the genome of some eukaryotic organisms and often consists of tandem repeats of DNA.