| DNA library | <molecular biology> A collection of DNA molecules, derived from restriction fragments that have been cloned in vectors, that includes all or part of the genetic material of an organism. (18 Nov 1997) |
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| DNA ligase | <enzyme, molecular biology> Enzyme involved in DNA replication. The DNA ligase of E. Coli seals nicks in one strand of double stranded DNA, a reaction required for linking precursor fragments during discontinuous synthesis on the lagging strand. Nicks are breaks in the phosphodiester linkage that leave a free 3_ OH and 5_ phosphate. The ligase from phage T4 has the additional property of joining two DNA molecules having completely base paired ends. DNA ligases are crucial in joining DNA molecules and preparing radioactive probes (by nick translation) in recombinant DNA technology. (18 Nov 1997) |
| DNA ligases | <enzyme> Poly(deoxyribonucleotide):poly(deoxyribonucleotide)ligases. Enzymes that catalyze the joining of preformed deoxyribonucleotides in phosphodiester linkage during genetic processes during repair of a single-stranded break in duplex DNA. The class includes both ATP and NAD. Registry number: EC 6.5.1.- (12 Dec 1998) |
| DNA ligation | <molecular biology> The joining of two DNA strands by their ends with a phosphodiester bond. (09 Oct 1997) |
| DNA markers | Segments of chromosomal DNA known to be linked with heritable traits or diseases. Although the markers themselves to not produce the conditions, they exist in concert with the genes responsible and are passed on with them. Certain markers, restriction fragment length polymorphisms, consist of segments of DNA that can be identified on autoradiographs (produced after digestion of the DNA by restriction enzymes and segregation of the resulting fragments through gel electrophoresis). (05 Mar 2000) |
| DNA methylation | <molecular biology> Process by which methyl groups are added to certain nucleotides in genomic DNA. This affects gene expression, as methylated DNA is not easily transcribed. The degree of methylation is passed on to daughter strands at mitosis by maintainance DNA methylases. Accordingly, DNA methylation is thought to play an important developmental role in sequentially restricting the transcribable genes available to distinct cell lineages. In bacteria, methylation plays an important role in the restriction systems, as restriction enzymes cannot cut sequences with certain specific methylations. (18 Nov 1997) |
| 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. (12 Dec 1998) |
| DNA modification | <molecular biology> A variety of chemical changes made to a DNA molecule just after it has been replicated. An example is DNA methylation. (09 Oct 1997) |
| DNA modification methylases | <enzyme> Enzymes that are part of the restriction-modification systems. They are responsible for producing a species-characteristic methylation pattern, on either adenine or cytosine residues, in a specific short base sequence in the host cell's own DNA. This methylated sequence will occur many times in the hosT-cell DNA and remain intact for the lifetime of the cell. Any DNA from another species which gains entry into a living cell and lacks the characteristic methylation pattern will be recognised by the restriction endonucleases of similar specificity and destroyed by cleavage. most have been studied in bacterial systems, but a few have been found in eukaryotic organisms. Registry number: EC 2.1.1.- (12 Dec 1998) |
| DNA molecules, recombinant | A combination of DNA molecules of different origin that are joined using recombinant DNA technology. (12 Dec 1998) |
| DNA mutational analysis | Biochemical identification of mutational changes in a nucleotide sequence. (12 Dec 1998) |
| DNA, neoplasm | DNA present in neoplastic tissue. (12 Dec 1998) |
| DNA N-glycosidase | <enzyme> Excises 3-methyladenine from alkylated DNA leaving an apurinic site with both 3' and 5' phosphodiester bonds intact, a preparatory step for nucleotide excision repair; excises hypoxanthine from deaminated DNA and polydeoxyribonucleotides; prefer EC 3.2.2.20 or EC 3.2.2.21 Registry number: EC 3.2.2.- Synonym: DNA glycosylase, methylpurine DNA glycosylase (26 Jun 1999) |
| DNA, nongenetic | Through the marvellous medium of the Internet, we have discovered that DNA need not refer to deoxyribonucleic acid. Specifically, in an e-mail entitled A day in the life of a specialist registrar from Glascow, Scotland we read that in gynaecology outpatient clinic, the specialist registrar (resident in the U.S.) at 12:10 Sorted out the DNA's (did not attends). We in the U. S. Might say the no-show when a patient does not present for his/her appointment. (12 Dec 1998) |
| DNA nucleotidylexotransferase | <enzyme> A non-template-directed DNA polymerase normally found in vertebrate thymus and bone marrow. It catalyses the elongation of oligo- or polydeoxynucleotide chains and is widely used as a tool in the differential diagnosis of acute leukaemias in man. Chemical name: Nucleoside-triphosphate:DNA deoxynucleotidylexotransferase Registry number: EC 2.7.7.31 (12 Dec 1998) |