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 determine 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 a double-stranded helical structure composed of two strands. Each strand consists of nucleotides, and each nucleotide is made up of a deoxyribose sugar, a nitrogenous base, and a phosphate group.

2. **Identify the Number of Base Pairs**:
- The question states that there are 20,000 base pairs in the DNA segment.

3. **Calculate the Total Number of Nucleotides**:
- Since DNA is double-stranded, each base pair corresponds to one nucleotide on each strand. Therefore, for 20,000 base pairs, there are:
- 20,000 nucleotides on one strand
- 20,000 nucleotides on the other strand
- This results in a total of 20,000 + 20,000 = 40,000 nucleotides.

4. **Determine the Number of Phosphate Groups**:
- Each nucleotide contains one phosphate group. Therefore, the total number of phosphate groups in the DNA segment is equal to the total number of nucleotides.
- Since we have 40,000 nucleotides, there will also be 40,000 phosphate groups.

5. **Conclusion**:
- The number of phosphate molecules in the DNA segment is 40,000.

### Final Answer:
The number of phosphate molecules in this DNA molecule is **40,000**.