An enzyme catalysing the removal of nucleotides from the ends of DNA is

Options

A. endonuclease
B. exonuclease
C. DNA ligase
D. Hind - II

Answer

To solve the question, "An enzyme catalyzing the removal of nucleotides from the ends of DNA is," we need to analyze each of the given options and their functions:

1. **Endonuclease**:
- Function: Endonucleases are enzymes that cut DNA at specific internal sites within the DNA molecule. They recognize specific sequences (restriction sites) and cleave the DNA at those locations, resulting in fragments of DNA.
- Conclusion: This option does not fit the requirement of removing nucleotides from the ends of DNA.

2. **Exonuclease**:
- Function: Exonucleases are enzymes that remove nucleotides from the ends of a DNA molecule. They can remove one nucleotide at a time from either the 5' or 3' end of the DNA strand. This process shortens the DNA molecule by removing nucleotides sequentially from the ends.
- Conclusion: This option directly matches the requirement of the question.

3. **DNA Ligase**:
- Function: DNA ligase is an enzyme that joins two DNA fragments together by forming phosphodiester bonds. It is primarily involved in DNA replication and repair, where it seals nicks in the DNA backbone.
- Conclusion: This option does not relate to the removal of nucleotides.

4. **Restriction Endonuclease**:
- Function: Similar to endonucleases, restriction endonucleases cut DNA at specific sequences but are often used in molecular cloning and genetic engineering. They do not remove nucleotides from the ends of DNA.
- Conclusion: This option also does not fit the requirement.

After analyzing all the options, the correct answer to the question is **Exonuclease**, as it specifically catalyzes the removal of nucleotides from the ends of DNA.

### Summary of Steps:
1. Identify the function of each enzyme option.
2. Eliminate options that do not match the requirement of removing nucleotides from the ends of DNA.
3. Conclude that the correct answer is Exonuclease.