A segment of DNA molecule contains 20,000 base pairs. What is the number of phosphate molecule in this DNA molecule ?

Options

A. 20000
B. 40000
C. 10000
D. 5000

Answer

To solve the problem of determining the number of phosphate molecules in a DNA segment that contains 20,000 base pairs, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of DNA**:
- DNA is composed of nucleotides, and each nucleotide consists of three components: a sugar molecule, a nitrogenous base, and a phosphate group.

2. **Identify Base Pairs**:
- In DNA, each base pair consists of two nucleotides (one from each strand). Therefore, if we have 20,000 base pairs, we need to calculate the total number of nucleotides.

3. **Calculate Total Nucleotides**:
- Since each base pair consists of two nucleotides, the total number of nucleotides in the DNA segment is:
\[ \text{Total Nucleotides} = \text{Number of Base Pairs} \times 2 = 20,000 \times 2 = 40,000 \]

4. **Determine Phosphate Molecules**:
- Each nucleotide contains one phosphate molecule. Therefore, the total number of phosphate molecules is equal to the total number of nucleotides.
\[ \text{Total Phosphate Molecules} = \text{Total Nucleotides} = 40,000 \]

5. **Final Answer**:
- Thus, the number of phosphate molecules in the DNA segment containing 20,000 base pairs is **40,000**.

### Summary:
The DNA segment with 20,000 base pairs contains **40,000 phosphate molecules**.

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