CBSE Class 12-science Answered

A homodimer is formed by two identical molecules while a heterodimer is formed by two different macromolecules.  For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length.

Restriction endonuclease EcoRI found in E.coli recognises the base sequence GAATTC in DNA duplex and cuts its strands between G and A.

It creates 4 nucleotide sticky ends with 5' end overhangs of AATT.  EcoRI endonuclease exists as a homodimer where each monomer binds to either side of DNA. The enzyme is a homodimer of a 31 kilodalton subunit consisting of one globular domain of the α/β architecture. Each subunit contains a loop which sticks out from the globular domain and wraps around the DNA when bound.