If base order in one chain of DNA is "ATCGA" then how many no. of H-bond found in DNA duplex :-

Options

A. 20
B. 12
C. 10
D. 11

Answer

To determine the number of hydrogen bonds in a DNA duplex given the base order in one chain as "ATCGA", we can follow these steps:

### Step 1: Identify the Base Pairing Rules
In DNA, the nitrogenous bases pair in a specific way:
- Adenine (A) pairs with Thymine (T) via **2 hydrogen bonds**.
- Cytosine (C) pairs with Guanine (G) via **3 hydrogen bonds**.

### Step 2: Write Down the Given Sequence
The sequence provided is:
- **A-T-C-G-A**

### Step 3: Determine the Complementary Sequence
To find the complementary strand, we replace each base with its pair:
- A → T
- T → A
- C → G
- G → C
- A → T

Thus, the complementary sequence will be:
- **T-A-G-C-T**

### Step 4: Count the Hydrogen Bonds
Now we will count the hydrogen bonds between the bases in the original sequence and the complementary sequence:
1. **A (2 H-bonds) - T**
2. **T (2 H-bonds) - A**
3. **C (3 H-bonds) - G**
4. **G (3 H-bonds) - C**
5. **A (2 H-bonds) - T**

### Step 5: Sum the Hydrogen Bonds
Now we add up the hydrogen bonds:
- A-T: 2
- T-A: 2
- C-G: 3
- G-C: 3
- A-T: 2

Total hydrogen bonds = 2 + 2 + 3 + 3 + 2 = **12 hydrogen bonds**.

### Conclusion
The total number of hydrogen bonds in the DNA duplex formed by the sequence "ATCGA" is **12**.