During isolation of DNA, addition of which of the following causes precipitation of purified DNA?

Options

A. Chilled ethanol
B. Ribonuclease enzyme
C. DNA polymerase
D. Proteases

Answer

To answer the question regarding which substance causes the precipitation of purified DNA during its isolation, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding DNA Isolation**:
- DNA isolation involves several steps, including cell lysis, removal of proteins and other contaminants, and finally, precipitation of DNA.

2. **Identifying the Role of Ethanol**:
- Chilled ethanol is commonly used in the DNA isolation process. When added to a solution containing DNA, it causes the DNA to precipitate out of the solution.

3. **Mechanism of Precipitation**:
- The addition of chilled ethanol reduces the solubility of DNA in the solution. DNA is more soluble in water, but when ethanol is added, it disrupts the hydration shell around the DNA molecules, leading to their aggregation and precipitation.

4. **Observing the Precipitation**:
- Upon the addition of chilled ethanol, the DNA appears as fine threads or a visible mass that can be collected. This process is often referred to as DNA spooling.

5. **Evaluating Other Options**:
- Ribonuclease enzyme: This enzyme cleaves RNA, not DNA, so it does not cause precipitation of DNA.
- DNA polymerase: This enzyme synthesizes DNA strands and does not participate in the precipitation process.
- Proteases: These enzymes degrade proteins and are not involved in DNA precipitation.

6. **Conclusion**:
- The correct answer to the question is chilled ethanol, as it is the substance that causes the precipitation of purified DNA during its isolation.

### Final Answer:
The addition of chilled ethanol causes the precipitation of purified DNA during its isolation.

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