What is the function of endonucleases?

The correct answer is Option (2) → To cut DNA at specific positions within the DNA

Nucleases are enzymes that break the phosphodiester bonds of nucleic acids. They are of two kinds. Exonucleases remove nucleotides from the ends of a DNA molecule. Endonucleases make cuts at specific positions within the DNA. Restriction enzymes such as EcoR I are endonucleases: each one recognises its own palindromic sequence and cuts both strands there.

Option (1) To remove nucleotides from the ends of DNA — Incorrect. Removing nucleotides from the ends of DNA is the work of exonucleases (“exo” means outside).

Option (2) To cut DNA at specific positions within the DNA — Correct. “Endo” means inside. Endonucleases cut within the DNA at specific positions.

Option (3) To remove nucleotides from the proteins — Incorrect. Proteins are made of amino acids, not nucleotides. Nucleases act on nucleic acids, and proteins are broken down by proteases.

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.”