Restriction Enzymes

From Indipedia: India's Wikipedia at OSDD

[edit] Restriction Enzymes

Restriction Enzymes are the usually dimers of identical subunits,analogous to the symmetry of their binding sites in DNA.Usually we call Restriction enzymes the molecular scissors(DNA cutting enzymes) found in bacteria and harvested from them for use.Because they can cut within the molecule, they are often called as Restriction enzymes.

A restriction enzyme recognizes and cut the DNA only at a particular sequence of nucleotides.For example, the bacterium Haemophilus aegypticus produces an enzyme named HaeIII that cuts DNA wherever its encounters the sequence, 5'GGCC3' in one strand and 3'CCGG5' in other.

The cut is made between the adjacent G and C.This particular sequence occurs at 11places in the circular DNA molecule of the virus phiX174 and 11 fragments are produced which when separated are sequenced.

When Restriction enzyme cut the DNA molecule it makes two cuts.Such action results in generating a 3'hydroxyl and 5'phosphate termini.

One type of cleavage results in blunt ended DNA fragments and the other type of cleavage generates cohesive ended molecules.The blunt ended molecules are produced when a restriction enzymes acts on the line of symmetry and the cohesive ended or sticky end are produced when a restriction enzymes act along the line of symmetry.

[edit] Uses of Restriction enzymes

1.Recombinant DNA technology. The availability of human insulin(for diabetes),human factor VIII(for males with Haemophilia A) and other protein used in human therapy, all were made possible by r-DNA technology.

2.Cloning

3.cDNA/genomic library construction

4.DNA mapping