The length of one complete turn of a DNA double helix is -

Options

A. 3.4 Å
B. 34 Å
C. 3.6 Å
D. 36 Å

Answer

To solve the question regarding the length of one complete turn of a DNA double helix, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of DNA**:
- DNA is a double helix made up of two strands that are coiled around each other.

2. **Identify Key Measurements**:
- According to the Watson and Crick model, the distance between two consecutive base pairs in DNA is approximately 0.34 nanometers (or 3.4 angstroms).

3. **Determine the Number of Base Pairs in One Turn**:
- One complete turn of the DNA double helix consists of 10 base pairs.

4. **Calculate the Length of One Complete Turn**:
- To find the length of one complete turn, multiply the number of base pairs by the distance between consecutive base pairs:
\[ \text{Length of one complete turn} = \text{Number of base pairs} \times \text{Distance between base pairs} \]
\[ \text{Length of one complete turn} = 10 \times 3.4 \text{ angstroms} = 34 \text{ angstroms} \]

5. **Select the Correct Option**:
- From the options provided (3.4 angstrom, 34 angstrom, 3.6 angstrom, 36 angstrom), the correct answer is **34 angstrom**.

### Final Answer:
The length of one complete turn of a DNA double helix is **34 angstroms**.

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