Restriction enzyme
An enzyme from bacteria that can recognize specific base sequences in DNA and cut the DNA at that site (the restriction site). A restriction enzyme acts as a biochemical scissors. Also called a restriction endonuclease. A restriction enzyme is a protein produced by bacteria that cleaves DNA at specific sites. Bacteria use restriction enzymes to defend against bacterial viruses called bacteriophages (or phage). When a phage infects a bacteria, it inserts its DNA into the bacteria so that it might be replicated. The restriction enzyme prevents replication of the phage DNA by cutting it into many pieces. Restriction enzymes were named for their ability to restrict, or limit, the number of strains of bacteriophage that can infect bacteria. Restriction enzymes can be isolated from bacteria and used in the laboratory to cut DNA. They are indispensable tools in recombinant DNA technology and genetic engineering. Each restriction enzyme recognizes a short, specific sequence of nucleotide bases (the four basic chemical subunits of the linear double-stranded DNA molecule— adenine, cytosine, thymine, and guanine). These stretches in the DNA are called recognition sequences and are randomly distributed throughout the DNA. Different bacterial species make restriction enzymes that recognize different nucleotide sequences. After a restriction endonuclease recognizes a sequence, it cuts through the DNA molecule by catalyzing the hydrolysis (splitting of a chemical bond by addition of a water molecule) of the bond between adjacent nucleotides. Bacteria prevent their own DNA from being degraded in this manner by disguising their recognition sequences. Enzymes called methylases add methyl groups (--CH3) to adenine or cytosine bases within the recognition sequence, which is thus modified and protected from the endonuclease. The restriction enzyme and its corresponding methylase constitute the restriction- modification system of a bacterial species. All restriction enzymes are different. There are three classes of restriction enzymes, designated types I, II, and III. Types I and III enzymes are similar in that both restriction and methylase activities are carried out by one large enzyme complex, in contrast to the type II system, in which the restriction enzyme is independent of its methylase. Type II restriction enzymes also differ from the other two types in that they cleave DNA at specific sites within the recognition site; the others cleave DNA randomly, sometimes hundreds of bases from the recognition sequence. Restriction enzymes were originally discovered and characterized by the molecular biologists Werner Arber, Hamilton O. Smith, and Daniel Nathans who shared the 1978 Nobel prize in medicine. The ability of restriction enzymes to cut DNA at precise locations has permitted researchers to isolate gene-containing fragments and recombine them with other molecules of DNA. More than 2,500 type II restriction enzymes have been identified from a variety of bacterial species. These enzymes recognize about 200 distinct sequences, which are four to eight bases in length.

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restriction enzyme n any of various enzymes that cleave DNA into fragments at specific sites in the interior of the molecule and are often used as tools in molecular analysis

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an enzyme, obtained from bacteria, that cuts DNA into specific short segments. Restriction enzymes are widely used in genetic engineering.

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restriction endonuclease.

Medical dictionary. 2011.

Look at other dictionaries:

  • restriction enzyme — or restriction endonuclease [en΄dō no͞o′klē ās΄, en΄dōnyo͞o′klē ās΄] n. any of various enzymes that chemically break DNA into strands at specific locations …   English World dictionary

  • Restriction enzyme — Glossary Restriction …   Wikipedia

  • restriction enzyme — Biochem. any of a group of enzymes that catalyze the cleavage of DNA molecules at specific sites: used for gene splicing in recombinant DNA technology and for chromosome mapping. [1960 65] * * * Protein (more specifically, an endonuclease)… …   Universalium

  • restriction enzyme — restriction endonuclease an enzyme, obtained from bacteria, that cuts DNA into specific short segments. Restriction enzymes are widely used in genetic engineering …   The new mediacal dictionary

  • restriction enzyme — noun any of the enzymes that cut nucleic acid at specific restriction sites and produce restriction fragments; obtained from bacteria (where they cripple viral invaders); used in recombinant DNA technology • Syn: ↑restriction endonuclease,… …   Useful english dictionary

  • restriction enzyme — (also restriction endonuclease) noun Biochemistry an enzyme with the property of cleaving DNA molecules at or near a specific sequence of bases …   English new terms dictionary

  • restriction enzyme — noun Date: 1965 any of various enzymes that cleave DNA into fragments at specific sites in the interior of the molecule called also restriction endonuclease …   New Collegiate Dictionary

  • restriction enzyme — See restriction endonuclease …   Dictionary of molecular biology

  • restriction enzyme —    An enzyme that cuts DNA internally at a specific, known sequence site …   Forensic science glossary

  • restriction enzyme — Synonym of restriction endonuclease …   Glossary of Biotechnology

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