In double helix model of DNA, the number of hydrogen bonds formed between guanine and cytosine is

Options

A. Two
B. One
C. Three
D. Four

Answer

To determine the number of hydrogen bonds formed between guanine and cytosine in the double helix model of DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of DNA**:
- DNA (Deoxyribonucleic acid) is composed of two strands that form a double helix. Each strand is made up of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base.

2. **Identify the Nitrogenous Bases**:
- The nitrogenous bases in DNA are divided into two categories: purines and pyrimidines.
- Purines include adenine (A) and guanine (G).
- Pyrimidines include cytosine (C) and thymine (T).

3. **Base Pairing Rules**:
- According to Chargaff's rules, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C).
- The pairing occurs due to hydrogen bonds between the bases.

4. **Determine the Number of Hydrogen Bonds**:
- Adenine (A) and thymine (T) are connected by **two hydrogen bonds**.
- Guanine (G) and cytosine (C) are connected by **three hydrogen bonds**.

5. **Conclusion**:
- Therefore, the number of hydrogen bonds formed between guanine and cytosine is **three**.

### Final Answer:
The number of hydrogen bonds formed between guanine and cytosine in the double helix model of DNA is **3**.

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