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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> DNA Polymerase DNA Pol DNA Topoisomerases
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DNA polymerase g (DNA pol g)
A eukaryotic polymerase required for replication of mitochondrial DNA. The enzyme is a single polypeptide inhibited by –SH group blocking agents.
DNA polymerase d (DNA pol d)
A eukaryotic polymerase that synthesis both lading and lagging strands and has proofreading function. It is multisubunit complex that binds an accessory factor proliferating cell nuclear antigen (PCNA), a cyclin, which functions as a sliding clamp similar to the b subunit of E. coli, enhancing processivity of the enzyme.
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DNA polymerase e (DNA pol e)
A eukaryotic polymerase structurally analogous to polymerases d but does not associate with PCNA. It may have a role in the replication fork or DNA repair.
DNA polymerases Enzymes that catalyses DNA synthesis on a DNA template. These are termed DNA dependent DNA Polymerases. These enzymes catalyse synthesis of DNA during replication as well as filling gaps following DNA damage, recombination and after removal of primer from the lagging strand. DNA polymerases are incapable of initiating de novo DNA synthesis and can only extend an RNA primer. All DNA polymerases catalyse DNA synthesis by virtue of their 5’→3’ polymerase and pyrophosphorylase activities. In addition, DNA polymerases possess 3’→5’ exonuclease activity, which serves a proofreading function, and or 5’→3’ exonuclease activity for primer excision and repair.
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DNA polymorphism
The existence of two or more alternative forms (alleles) of a chromosomal locus that vary in nucleotide sequence or contain variable numbers of repeated nucleotide units. See allele.
DNA probes
A labelled DNA molecules (Including cDNA; conserve genes, whole chromosomes, or whole genomes) used to hybridise with a complementary DNA/RNA sequence to identify microorganisms to measure DNA-DNA homologies, or to Group subspecies. The DNA probe is labelled using 32P, 125l or biotin. DNA probes are used in dot blot assays, Southern blot assays, and DNA: RNA hybrid specific antibody tests. DNA probes provide a specific, sensitive, rapid, and inexpensive replacement for cell culture techniques for diagnosing infections.
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DNA repair
A variety of mechanisms that repair damaged DNA. These include photoreactivation, excision repair, mismatch repair, SOS repair, double strand break repair and recombination repair.DNA repair genes Genes that encode proteins involved in correcting DNA damage.
DNA, repetitive
Sequences repeated many times on the genome that vary in length from 3-5base pairs to 300 base pairs. These are found in hundreds to thousands of copies in the genome. Satellite DNA, one of the classes of repetitive DNA forms a distinct band from the bulk of chromosomal DNA in a CsCl gradient.
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DNA replicase
The complete set of enzymes and proteins that is required for DNA replication.
DNA replication
The process by which DNA makes exact copies of itself, using a number of enzymes including DNA polymerase.
DNA profiling
Refers to various methods for analyzing DNA to establish the identity of an individual. See DNA fingerprinting.
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DNA primase
An enzyme that catalyses the synthesis of short RNA primers that initiate the synthesis of DNA strands.
DNA rescue
A technique for cloning genes in bacteria or yeast by transforming plasmids with normal genes into a host containing a mutation that inactivates a specific function such as synthesis of a particular amino acid. If the added plasmid restores function it indicates that the plasmid contains the gene of interest.
DNA polymerase e (DNA pol e)
A eukaryotic polymerase structurally analogous to polymerases d but does not associate with PCNA. It may have a role in the replication fork or DNA repair.
DNA RNA hybrid
A DNA RNA duplex containing one strand of DNA and one complementary RNA strand. Thee hybrids can be created experimentally. They are also formed when chromosomal DNA is fragmented, heated and mixed with RNA transcripts.
DNA sequence
The order of base pairs in a DNA fragment, gene chromosome of the entire genome
DNA sequencing
Methods for determining the nucleotide sequence of a DNA fragment. Two method are available for sequencing: the Maxam and Gilbert method (chemical degradation), that uses different chemicals to break the DNA into fragments at specific bases; and Sanger’s enzymatic method (dideoxy or chain terminating method) that uses DNA polymerase to synthesis new DNA chains and dideoxynucleotide (chain terminators) to stop DNA synthesis randomly as it grows. In both techniques, the DNA fragments are separated by polyacrylamide gel electrophoresis and the sequence read directly from the gel.
DNA supercoiling
The coiling of DNA upon itself resulting from bending, overwinding or underwinding of the DNA duplex.
DNA topoisomerases
A family or enzymes that relax the torsional strain generated when Helicases unwind the DNA duple during replication, recombination and transcription. These enzymes introduces a ‘swivel’ into DNA just ahead of the replication fork by causing a transient break in DNA that is rapidly sealed. While most topoisomerases can only catalyse relaxation of supercoils, E. coil DNA gyrase can also generate negative supercoils and reverse gyrase from S. acidocaldarius can generate positive supercoils. Topoisomerases also remove knots and catalyse catenation and decatenation.
In eukaryotes, topoisomerases form an integral part of the nuclear scaffold facilitating the organisation of DNA into functional domains and are involved in the separation of sister chromatids during mitosis. Topoisomerases attach covalently to DNA and catalyse reversible cleavage of a phospho-diester bond. The phospho-diester bond reforms after the enzyme dissociates from the DNA. Topoisomerase are classified into type I and type II based on whether they cleave one or both strands of DN and change the linking number in steps of one or two respectively.
DNA transformation
See Transfection, Transformation.
DNA vaccine
A vaccine in which antigen DNA is injected and expressed in host cells. The expressed vaccine elicits an immune response.
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