Question

Which enzymes are molecular scissors?

Answer 1

Restriction enzymes: Restriction enzymes are also called "molecular scissors" as they cleave DNA at or near specific recognition sequences known as restriction sites.

These are of two kinds:- Exonucleases and Endonucleases

1. Exonucleases remove nucleotides from the ends of the DNA whereas, endonucleases make cuts at specific positions within the DNA.
2. Each restriction endonuclease recognizes specific palindromic nucleotide sequences in the DNA that reads the same on the two strands when the orientation of the reading is kept the same.
3. The restriction enzymes cut DNA at a specific base sequence, which is known as the recognition sequence.

Naming restriction enzymes-

1. The first letter of the name comes from the genus.
2. The second two letters come from the species of the prokaryotic cell from which enzyme was isolated.
3. For e.g., EcoRI comes from Escherichia coli RY 13., In EcoRI, the letter ‘R’ is derived from the name of the strain.
4. Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria.
5. So far, 900 restriction enzymes that have been isolated from over 230 strains of bacteria.