Which of the following chemical substance acts as molecular sieve?

Options

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

Answer

To determine which chemical substance acts as a molecular sieve, we need to analyze each of the given options:

1. **DNA ligase**: This enzyme is responsible for sealing two segments of DNA together. It does not act as a sieve, so this option is incorrect.

2. **Endonuclease**: This enzyme cleaves the phosphodiester bonds within a nucleic acid chain. Its primary function is to cut DNA or RNA, not to act as a sieve. Therefore, this option is also incorrect.

3. **DNA polymerase**: This enzyme plays a crucial role in DNA replication by synthesizing new strands of DNA. It does not function as a molecular sieve, making this option incorrect as well.

4. **Agarose**: Agarose is a gel used in gel electrophoresis. It serves as a molecular sieve because it separates DNA molecules based on their size. Smaller DNA fragments can move through the gel more easily than larger ones, effectively acting as a strainer or sieve. Thus, this option is correct.

Based on the analysis, the correct answer is **agarose**, as it acts as a molecular sieve in gel electrophoresis.

### Steps Summary:
1. Analyze DNA ligase – Incorrect, does not act as a sieve.
2. Analyze endonuclease – Incorrect, does not act as a sieve.
3. Analyze DNA polymerase – Incorrect, does not act as a sieve.
4. Analyze agarose – Correct, acts as a molecular sieve in gel electrophoresis.