Saturday 14 May 2016

Restriction endonuclease

Restriction endonuclease-

These are DNA cutting enzymes within a particular sequence  after recognition ,as they are often cut within the dna so called restriction endonuclease.Hamilton Smith isolated a restriction enzyme from the bacterium Haemophilous influenzae called as HindII, recognize 6 base pair dsDNA sequence.

Occurance - Found in bacteria.(source)
Function     - In order to sequence DNA,it is first necessasry to cut into smaller fragments.
Types         - (Acc. to their recognition and  specificity of cleavage.)

1.Isoschizomer-(iso=similar ,schizomer=cleavage of Dna) Similar type of cleavage in a dna from 2 different sources. called isoschizomer.For example, 
Sph I (CGTAC/G) and Bbu I (CGTAC/G) are isoschizomers of each other.Can recognize both methylated and non methylated forms.

2 .Neoschizomer-.An enzyme that recognizes the same sequence but cuts it differently( different cleavage site) is a  Neoschizomer.They  are a specific type (subset) of Isoschizomers. For example, S
ma I (CCC/GGG) and Xma I (C/CCGGG) are neoschizomers of each other.


Image source credit http://sivabio.50webs.com/dna%20cl48.gif


3. Isocaudamer-An enzyme that recognizes slightly different sequence, but produces the same ends is a isocaudamer.
               
Recognition sites are same for ( isoschizomer  & neoschizomer ). All are isolated from 2 different sources.In isocaudamer  recognition sites are different but the product is with similar type of ends.


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