Canadian Medical Guide > Chemicals and Drugs > Nucleic Acids, Nucleotides, and Nucleosides > Nucleic Acids > DNA > DNA, Circular Terms and Definitions

DNA, Circular

Medical Definition:	Any of the covalently closed DNA molecules found in bacteria, many viruses, mitochondria, plastids, and plasmids. Small, polydisperse circular DNA's have also been observed in a number of eukaryotic organisms and are suggested to have homology with chromosomal DNA and the capacity to be inserted into, and excised from, chromosomal DNA. It is a fragment of DNA formed by a process of looping out and deletion, containing a constant region of the mu heavy chain and the 3'-part of the mu switch region. Circular DNA is a normal product of rearrangement among gene segments encoding the variable regions of immunoglobulin light and heavy chains, as well as the T-cell receptor. (Riger et al., Glossary of Genetics, 5th ed & Segen, Dictionary of Modern Medicine, 1992)
Guide Notes:	IM; /drug eff /ultrastruct permitted
Previously Indexed:	DNA (1966-1972)

DNA, Circular Categories.

	DNA, Chloroplast - Deoxyribonucleic acid that makes up the genetic material of CHLOROPLASTS.
	DNA, Mitochondrial - Double-stranded DNA of MITOCHONDRIA. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal RNAs, transfer RNAs, and about 10 proteins.
	DNA, Superhelical - Circular duplex DNA isolated from viruses, bacteria and mitochondria in supercoiled or supertwisted form. This superhelical DNA is endowed with free energy. During transcription, the magnitude of RNA initiation is proportional to the DNA superhelicity.

DNA, Circular Medical Definitions and Terms

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