Which of the following statements is correct?

Options

A. Adenine pairs with thymine through one H-bond
B. Adenine pairs with thymine through three H-bonds.
C. Adenine does not pair with thymine.
D. Adenine pairs with thymine through two H-bonds.

Answer

To determine which statement is correct regarding the pairing of adenine and thymine in DNA, we can analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding DNA Structure**:
- DNA is composed of a sugar-phosphate backbone and nitrogenous bases.
- The nitrogenous bases are categorized into two groups: purines (adenine and guanine) and pyrimidines (cytosine and thymine).

2. **Base Pairing Rules**:
- In DNA, adenine (A) pairs with thymine (T).
- Cytosine (C) pairs with guanine (G).

3. **Hydrogen Bonds in Base Pairing**:
- The pairing between adenine and thymine involves hydrogen bonds.
- Specifically, adenine forms **two hydrogen bonds** with thymine.

4. **Evaluating the Statements**:
- **Statement 1**: Adenine pairs with thymine through one hydrogen bond. (Incorrect)
- **Statement 2**: Adenine pairs with thymine through three hydrogen bonds. (Incorrect)
- **Statement 3**: Adenine does not pair with thymine. (Incorrect)
- **Statement 4**: Adenine pairs with thymine through two hydrogen bonds. (Correct)

5. **Conclusion**:
- The correct statement is that adenine pairs with thymine through **two hydrogen bonds**.

### Final Answer:
The correct statement is: **Adenine pairs with thymine through two hydrogen bonds.**

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