How many nucleotides will be present in a DNA of 20000 base pairs

Options

A. 4000
B. 40000
C. 20000
D. 2000

Answer

To determine how many nucleotides are present in a DNA molecule with 20,000 base pairs, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of DNA**:
- DNA is composed of nucleotides, which are the building blocks of the DNA molecule. Each nucleotide consists of a nitrogenous base, a sugar, and a phosphate group.

2. **Identify Base Pairs**:
- In DNA, the nitrogenous bases pair up to form base pairs. The common pairs are adenine (A) with thymine (T) and guanine (G) with cytosine (C).

3. **Determine the Relationship Between Base Pairs and Nucleotides**:
- Each base pair consists of two nucleotides. For example, one base pair (A-T or G-C) includes one nucleotide from each of the two bases.

4. **Calculate the Total Number of Nucleotides**:
- Since each base pair contains two nucleotides, we can calculate the total number of nucleotides in a DNA molecule with 20,000 base pairs by multiplying the number of base pairs by 2.
- Calculation:
\[ \text{Total nucleotides} = \text{Number of base pairs} \times 2 \]
\[ \text{Total nucleotides} = 20,000 \times 2 = 40,000 \]

5. **Conclusion**:
- Therefore, the total number of nucleotides present in a DNA molecule with 20,000 base pairs is **40,000**.

### Final Answer:
**40,000 nucleotides**

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