How many nucleotides are found in one spiral of B-DNA?

Options

A. 5
B. 10
C. 20
D. 25

Answer

To determine how many nucleotides are found in one spiral of B-DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understand B-DNA Structure**: B-DNA is a right-handed double helix structure. Each complete turn of the helix contains a specific number of base pairs.

2. **Identify the Base Pair Turn**: In B-DNA, one complete turn of the helix consists of approximately 10.5 base pairs.

3. **Relate Base Pairs to Nucleotides**: Each base pair consists of two nucleotides (one from each strand of the DNA). Therefore, to find the number of nucleotides in one complete turn, we need to multiply the number of base pairs by 2.

4. **Calculate the Number of Nucleotides**:
- Number of base pairs in one turn = 10.5
- Number of nucleotides = 10.5 base pairs × 2 nucleotides/base pair = 21 nucleotides.

5. **Consider the Options**: The options given in the question were 5, 10, 20, and 25. Since 21 is not listed, we should round to the nearest provided option. The closest option is 20.

6. **Final Answer**: Therefore, the number of nucleotides found in one spiral of B-DNA is approximately 20.

### Final Answer:
The correct answer is **20 nucleotides**.

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