Question

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

Answer 1

A restriction enzyme is a type of protein that is capable of recognizing a specific sequence of nucleotides and capable of cutting DNA at a specific site. These enzymes are one class of the broader endonuclease group of enzymes.

Complete answer:
- Restriction enzymes are present in bacteria and other prokaryotic organisms. Restriction enzymes are also called restriction endonucleases.
- These enzymes identify specific sequences in DNA and bind to them. These sites are known as restriction sites. There are a number of restriction enzymes present in bacteria. More than 800 restriction enzymes have been isolated by different scientists which can recognize or identify more than 100 restriction sites in all. Each restriction enzyme can recognize or identify only a single or few restriction sites. Once these enzymes identify and bind to the restriction sites, they make a cut at or near these sites cleaving the DNA.
- EcoRI and smaI are the two examples of restriction enzymes.
- The source of EcoRI restriction enzyme is E.coli RY 13 bacteria. EcoRI makes a staggered cut in DNA creating two sticky ends.
- The source of smaI restriction enzyme is Serratia marcescens. smaI makes a straight cut in DNA creating two blunt ends

Note: Restriction enzymes are very helpful for bacteria in protecting them from viruses. A restriction enzyme is used by bacteria against viruses known as bacteriophages/phages. Bacteriophages are bacteria infecting viruses. They insert their DNA into bacterial DNA for replication. The bacterial restriction enzymes protect the replication of viral DNA by cutting it into a number of pieces. Thus, these enzymes restrict the number of bacteriophages that can infect the bacteria. Hence, they are known as restriction enzymes.