Which purine & pyrimidine bases are paired together by H- bonds in DNA-

Options

A. `AC&AT`
B. `GC&AT`
C. `GA&TC`
D. None of the above

Answer

To answer the question about which purine and pyrimidine bases are paired together by hydrogen bonds in DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Types of Bases**:
- DNA contains two types of nitrogenous bases: purines and pyrimidines.
- Purines include adenine (A) and guanine (G).
- Pyrimidines include cytosine (C) and thymine (T).

2. **Understand Base Pairing**:
- In DNA, purines pair with pyrimidines through hydrogen bonds.
- The specific pairings are:
- Adenine (A) pairs with Thymine (T).
- Guanine (G) pairs with Cytosine (C).

3. **Determine the Number of Hydrogen Bonds**:
- Adenine and Thymine form 2 hydrogen bonds.
- Guanine and Cytosine form 3 hydrogen bonds.

4. **Summarize the Pairings**:
- The correct pairs of bases in DNA are:
- A (Adenine) with T (Thymine)
- G (Guanine) with C (Cytosine)

5. **Conclude the Answer**:
- Therefore, the purine and pyrimidine bases paired together by hydrogen bonds in DNA are:
- Adenine (A) with Thymine (T)
- Guanine (G) with Cytosine (C)

### Final Answer:
- Adenine (A) pairs with Thymine (T) and Guanine (G) pairs with Cytosine (C) through hydrogen bonds in DNA.

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