The number of hydrogen bonds present in the sequence of a stretch of a double helical DNA
5. ATGCCTAA 3. is

Options

A. 16
B. 19
C. 24
D. 20

Answer

To determine the number of hydrogen bonds present in the given DNA sequence 5'-ATGCCTAA-3', we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Complementary Strand**:
The given DNA sequence is 5'-ATGCCTAA-3'. The complementary strand will be 3'-TACGGATT-5'.

2. **Pair the Bases**:
The base pairing rules in DNA are as follows:
- Adenine (A) pairs with Thymine (T) with **2 hydrogen bonds**.
- Guanine (G) pairs with Cytosine (C) with **3 hydrogen bonds**.

3. **List the Base Pairs**:
From the sequence:
- A (from ATGCCTAA) pairs with T (from TACGGATT) → 2 hydrogen bonds
- T pairs with A → 2 hydrogen bonds
- G pairs with C → 3 hydrogen bonds
- C pairs with G → 3 hydrogen bonds
- C pairs with G → 3 hydrogen bonds
- T pairs with A → 2 hydrogen bonds
- A pairs with T → 2 hydrogen bonds

4. **Count the Hydrogen Bonds**:
Now, we can sum the hydrogen bonds:
- A-T: 2
- T-A: 2
- G-C: 3
- C-G: 3
- C-G: 3
- T-A: 2
- A-T: 2

Total = 2 + 2 + 3 + 3 + 3 + 2 + 2 = **19 hydrogen bonds**.

5. **Conclusion**:
Therefore, the total number of hydrogen bonds present in the sequence 5'-ATGCCTAA-3' is **19**.