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. Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones. Each restriction endonuclease recognises a specific nucleotide sequences in the DNA.
Which statement is correct about endonuclease?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Cuts deoxyribonucleotide at specific position
Option (1) Removes nucleotide from the ends of DNA — Incorrect. Removing nucleotides from the ends is the work of exonucleases.
Option (2) Add the nucleotide at the end of DNA — Incorrect. Nucleases break nucleic acids; they do not add nucleotides. Exonucleases remove nucleotides from the ends of DNA, and joining DNA pieces is the work of DNA ligase.
Option (3) Cuts deoxyribonucleotide at specific position — Correct. Endonucleases cut DNA at specific positions within the molecule, while exonucleases remove nucleotides from its ends. Restriction endonucleases cut at their recognition sequence.
Option (4) Cuts ribonucleotide at specific position — Incorrect. Ribonucleotides are the units of RNA. The passage says endonucleases make cuts at specific positions within the DNA, which is made of deoxyribonucleotides.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
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.”