The numberof 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 DNA sequence 5' ATGCCTAA 3', we can follow these steps:

### Step-by-Step Solution:

1. **Identify the DNA Sequence and Its Complement**:
- The given DNA sequence is 5' ATGCCTAA 3'.
- The complementary strand will run in the opposite direction (3' to 5') and will be based on the pairing rules of nitrogenous bases:
- Adenine (A) pairs with Thymine (T) with 2 hydrogen bonds.
- Cytosine (C) pairs with Guanine (G) with 3 hydrogen bonds.

2. **Write the Complementary Strand**:
- The complementary bases for the sequence ATGCCTAA are:
- A (5') pairs with T (3')
- T (5') pairs with A (3')
- G (5') pairs with C (3')
- C (5') pairs with G (3')
- C (5') pairs with G (3')
- T (5') pairs with A (3')
- A (5') pairs with T (3')
- Therefore, the complementary strand is 3' TACGGATT 5'.

3. **Count the Hydrogen Bonds**:
- Now we will count the hydrogen bonds for each base pair:
- A (2 H-bonds) - T
- T (2 H-bonds) - A
- G (3 H-bonds) - C
- C (3 H-bonds) - G
- C (3 H-bonds) - G
- T (2 H-bonds) - A
- A (2 H-bonds) - T
- The pairs are as follows:
- A-T: 2 H-bonds
- T-A: 2 H-bonds
- G-C: 3 H-bonds
- C-G: 3 H-bonds
- C-G: 3 H-bonds
- T-A: 2 H-bonds
- A-T: 2 H-bonds

4. **Calculate Total Hydrogen Bonds**:
- Total from A-T pairs: 2 + 2 + 2 + 2 = 8 H-bonds
- Total from G-C pairs: 3 + 3 + 3 = 9 H-bonds
- Therefore, the total number of hydrogen bonds = 8 + 9 = 17 H-bonds.

5. **Final Answer**:
- The total number of hydrogen bonds present in the DNA sequence 5' ATGCCTAA 3' is **17**.