Question

Which enzyme is known as genetic scissors?

Answer 1

Restriction enzymes: They are known as molecular scissors. They are endonucleases and cut the DNA at specific points.

1. Restriction enzymes belong to a larger class of enzymes.
2. Restriction enzymes are called as molecular scissors because these enzymes cut DNA at specific sites.
3. The first restriction endonuclease is Hind II.
4. The restriction enzymes cut DNA at specific base sequence, and these specific base sequence is known as the recognition sequence.
5. The convention for naming restriction enzymes – The first letter of the name comes from the genus, the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., Eco RI comes from Escherichia coli RY 13, in Eco RI, the letter ‘R’ is derived from the name of strain.
   Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria.
   900 restriction enzymes that have been isolated from over 230 strains of bacteria.
6. These are of two kinds:- Exonucleases and Endonucleases
7. Exonucleases remove nucleotides from the ends of the DNA whereas, endonucleases make cuts at specific positions within the DNA.
8. Each restriction endonuclease recognizes a specific palindromic nucleotide sequences in the DNA.
9. The palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same.