Which of the following statements about restriction enzymes is incorrect?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The name of a restriction enzyme comes from the bacteriophage from which it was isolated.
A restriction enzyme takes its name from the bacterium it is isolated from, not from a bacteriophage. In fact these enzymes were found because they restrict the growth of bacteriophages inside bacteria.
Option (1) Restriction enzymes belong to a larger class of enzymes called nucleases. — A correct statement. Nucleases are of two kinds, exonucleases and endonucleases, and restriction enzymes belong to this larger class.
Option (2) The name of a restriction enzyme comes from the bacteriophage from which it was isolated. — An incorrect statement. The first letter of the name comes from the genus and the next two letters from the species of the prokaryotic cell from which the enzyme was isolated, e.g. EcoRI from Escherichia coli RY 13.
Option (3) Each restriction enzyme recognises a specific palindromic nucleotide sequence in the DNA. — A correct statement. Each restriction endonuclease looks for its own palindromic sequence and binds there before cutting.
Option (4) Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome site. — A correct statement. Cutting a little away from the centre of the site, between the same two bases on both strands, leaves the single stranded sticky ends.
NCERT Extract:
Restriction Enzymes – “… The convention for naming these enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from Escherichia coli RY 13. … Restriction enzymes belong to a larger class of enzymes called nucleases.”
Restriction Enzymes – “… Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA.”
Restriction Enzymes – “… Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites, but between the same two bases on the opposite strands.”