Exonucleases and Endonucleases
- Exonucleases: Restrictions exonucleases, such as exonuclease I, exonuclease II, etc., are largely responsible for hydrolyzing the terminal nucleotides from the end of DNA or RNA molecules in either a 5′ to 3′ or 3′ to 5′ direction.
- Endonuclease: Restrictions endonucleases identify certain base sequences (restricted sites) within DNA or RNA molecules and catalyze the breakdown of internal phosphodiester bonds with enzymes like EcoRI, Hind III, and BamHI.
Restriction Enzymes
Restriction enzyme is a bacterial protein that cleaves DNA at particular locations, these sites are called restricted sites. The restriction enzymes guard against bacteriophages in living bacteria. They identify the bacteriophage and cleave it at its restriction sites, destroying its DNA. Important genetic engineering tools include restriction enzymes. They may be separated from bacteria and applied in research facilities. The recognition sequences, or short and distinct nucleotide sequences, are recognized by restriction enzymes in DNA. When a DNA sequence is recognized by the restriction enzyme, it hydrolyzes the bond between neighboring nucleotides and cleaves the DNA molecule. The bacteria use the enzyme methylases to add the methyl group at the adenine or cytosine bases within the recognition sequence, preventing the DNA sequences from disintegrating.