Which of the following is considered as molecular glue ?

Options

A. DNA polymerase
B. Restriction enzyme
C. RNA polymerase
D. DNA ligase

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which of the given options is considered as "molecular glue." Molecular glue refers to a substance that can join two different molecules together.

2. **Analyzing the Options**:
- **Option 1: DNA Polymerase**: This enzyme is involved in DNA replication. It adds nucleotides to a growing DNA strand but does not join different DNA fragments together. Therefore, it is not considered molecular glue.

- **Option 2: Restriction Enzyme**: This enzyme cuts DNA at specific sites. It is involved in breaking down DNA rather than joining it. Thus, it is also not molecular glue.

- **Option 3: RNA Polymerase**: This enzyme synthesizes RNA from a DNA template during transcription. While it plays a crucial role in RNA synthesis, it does not join DNA fragments, making it an incorrect choice as well.

- **Option 4: DNA Ligase**: This enzyme is responsible for joining two DNA fragments together. It acts like a molecular glue by sealing nicks in the DNA backbone and connecting different segments of DNA, especially in processes like DNA replication and recombinant DNA technology.

3. **Conclusion**: Based on the analysis, the correct answer is **DNA Ligase**, as it is the enzyme that acts as molecular glue by joining different DNA fragments together.