Sticky ends of two DNA strands are joined by the action of enzyme

Options

A. DNA ligase
B. Endonuclease
C. Exonuclease
D. DNA polymerase

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which enzyme is responsible for joining the sticky ends of two DNA strands.

2. **Identifying the Options**: The options provided are:
- DNA ligase
- Endonuclease
- Exonuclease
- DNA polymerase

3. **Analyzing Each Option**:
- **DNA Ligase**: This enzyme is known for its role in joining two DNA strands by forming a bond between them. It specifically connects the phosphate group of one DNA strand with the deoxyribose sugar of another strand.
- **Endonuclease**: This type of enzyme cuts DNA at specific sites, but does not join DNA strands.
- **Exonuclease**: Similar to endonucleases, exonucleases remove nucleotides from the ends of DNA strands, and do not facilitate the joining of strands.
- **DNA Polymerase**: This enzyme is primarily involved in DNA replication and synthesizing new DNA strands, but it does not join sticky ends.

4. **Conclusion**: Since DNA ligase is the enzyme that connects the sticky ends of DNA strands by forming bonds, it is the correct answer.

5. **Final Answer**: The sticky ends of two DNA strands are joined by the action of **DNA ligase**.

---