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

Options

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

Answer

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

### Step-by-Step Solution:

1. **Understanding DNA Isolation**:
- DNA isolation is a multi-step process that involves breaking down cell walls and membranes, digesting cellular components, and purifying the DNA from other biomolecules like proteins and RNA.

**Hint**: Recall that DNA isolation involves multiple steps, including cell lysis and purification.

2. **Identifying the Precipitation Step**:
- After the digestion of cellular components, the DNA remains in a soluble form. The final step of the isolation process is the precipitation of this soluble DNA.

**Hint**: Think about what happens to DNA after it has been isolated and is still in solution.

3. **Role of Chilled Ethanol**:
- Chilled ethanol is commonly used in the precipitation step because it causes the DNA to aggregate and become visible as fine threads. This process is known as DNA spooling.

**Hint**: Consider which substances are typically used to precipitate nucleic acids in laboratory protocols.

4. **Evaluating the Options**:
- **Chilled Ethanol**: Correct option, as it is used for DNA precipitation.
- **Ribonuclease enzyme**: Incorrect, as it is used to degrade RNA, not for precipitation.
- **DNA Polymerase**: Incorrect, as it is involved in DNA synthesis, not isolation.
- **Proteases**: Incorrect, as they are used to digest proteins, not for precipitation.

**Hint**: Analyze each option based on its function in the DNA isolation process.

5. **Conclusion**:
- The correct answer is **Chilled Ethanol**, as it is the agent that causes the precipitation of purified DNA during the isolation process.

### Final Answer:
**Chilled Ethanol** causes the precipitation of purified DNA during its isolation.