Question

Read the following statements and choose the appropriate option.
Statement 1 - The enzyme catalysing the removal of nucleotides from the ends of DNA is exonuclease.
Statement 2 - The enzyme that cleaves phosphodiester bonds at any site within the DNA is exonuclease.
Statement 3 - The enzyme that cleaves phosphodiester bonds at specific sites within the DNA is endonuclease.

• A. Statements 1 and 2 are correct, but statement 3 is incorrect
• B. Statements 1 and 3 are correct, but statement 2 is incorrect
• C. Statements 2 and 3 are correct, but statement 1 is incorrect
• D. Statements 1, 2 and 3 are correct

Answer 1

The correct option is B Statements 1 and 3 are correct, but statement 2 is incorrect

Nucleases are the class of enzymes that hydrolyse the phosphodiester bond present in the backbone of nucleic acids (RNA and DNA). Nucleases are of two types - exonucleases and endonucleases.

• Exonucleases cleave phosphodiester bonds between consecutive nucleotides in a polynucleotide at their terminal ends (either 5’ or 3’), usually one nucleotide at a time.
• Endonucleases cleave the phosphodiester bonds present between the two nucleotides within DNA. Restriction endonucleases are a type of endonuclease that recognise specific DNA sequences, referred to as recognition sequences, and cleave phosphodiester bonds at or near to those sequences.

Hence, Statements 1 and 3 are correct, but statement 2 is incorrect.