Question

What are restriction enzymes? Mention any two restriction enzymes and their source.

Answer 1

A restriction enzyme is an enzyme that cleaves DNA into fragments at or near specific recognition sites within the molecule known as restriction sites. Restrictions enzymes are one class of the broader endonuclease group of enzymes. Restriction enzymes are commonly classified into five types, which differ in their structure and whether they cut their DNA substrate at their recognition site, or if the recognition and cleavage sites are separate from one another. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix. These enzymes are found in bacteria and archaea and provide a defense mechanism against invading viruses.

• EcoRI: EcoRI (pronounced "eco R one") is a restriction endonuclease enzyme isolated from species E. coli. The Eco part of the enzyme's name originates from the species from which it was isolated, while the R represents the particular strain, in this case, RY13. The last part of its name, the I, denotes that it was the first enzyme isolated from this strain. EcoRI is a restriction enzyme that cleaves DNA double helices into fragments at specific sites.
• BamH I: BamH I isolated from Bacillus amyloliquefaciens is a type II restriction endonuclease, having the capacity for recognizing short sequences (6 b.p.) of DNA and specifically cleaving them at a target site. BamH I binds at the recognition sequence 5'-GGATCC-3' and cleaves these sequences just after the 5'-guanine on each strand. This cleavage results in sticky ends which are 4 b.p. long. In its unbound form, BamH I displays a central b sheet, which resides in between α-helices.