Given below are two statements:
Statement I: Restriction enzymes belong to a larger class of enzymes called nucleases.
Statement II: Exonucleases make cuts at specific positions within the DNA, whereas endonucleases remove nucleotides from the ends of the DNA.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is correct but Statement II is incorrect
Statement I: Restriction enzymes belong to a larger class of enzymes called nucleases. — True. Nucleases are enzymes that break down nucleic acids. Restriction enzymes are one group of them; they cut DNA at particular base sequences.
Statement II: Exonucleases make cuts at specific positions within the DNA, whereas endonucleases remove nucleotides from the ends of the DNA. — False. The two roles are swapped. Exonucleases (“exo” means outside) remove nucleotides from the ends of the DNA. Endonucleases (“endo” means inside) make cuts at specific positions within the DNA, and restriction endonucleases are of this kind.
NCERT Extract:
Restriction Enzymes – “… Restriction enzymes belong to a larger class of enzymes called nucleases. These are of two kinds; exonucleases and endonucleases. Exonucleases remove nucleotides from the ends of the DNA whereas, endonucleases make cuts at specific positions within the DNA. Each restriction endonuclease functions by ‘inspecting’ the length of a DNA sequence.”