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

Options

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

Answer

To answer the question regarding the isolation of DNA and the addition that causes the precipitation of purified DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding DNA Isolation**: The process of isolating DNA involves three main steps: lysis, precipitation, and purification. Each step plays a crucial role in obtaining pure DNA from the sample.

2. **Step 1 - Lysis**: In the first step, the cell membranes are broken down (lysed) to release the DNA into the solution. This is typically done using a lysis buffer that contains detergents and enzymes.

3. **Step 2 - Precipitation**: After lysis, the next step is to precipitate the DNA out of the solution. This is where the question focuses. The precipitation step is crucial for separating the DNA from other cellular components.

4. **Step 3 - Addition of Chilled Ethanol**: The key to precipitating the purified DNA is the addition of chilled ethanol (or isopropanol). When chilled ethanol is added to the solution containing the DNA, it causes the DNA to aggregate and precipitate out of the solution.

5. **Observation**: Upon the addition of chilled ethanol, the purified DNA appears as fine threads, which can be spooled onto a glass rod. This is a visual indication that the DNA has been successfully precipitated.

6. **Conclusion**: Therefore, the addition of chilled ethanol is what causes the precipitation of purified DNA during the isolation process.

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

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