The sequence of N - bass in one strand DNA is ' 3 TAC CAC TCC ATA ATT 5 ' How many purines will be present in the Watson crick structure of this DNA ?

Options

A. 18
B. 5
C. 15
D. 10

Answer

To determine the number of purines present in the Watson-Crick structure of the given DNA sequence, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the DNA Strand**:
The given DNA sequence is '3 TAC CAC TCC ATA ATT 5'. This is the sequence of one strand of DNA.

2. **Determine the Complementary Strand**:
According to the Watson-Crick base pairing rules:
- Adenine (A) pairs with Thymine (T)
- Guanine (G) pairs with Cytosine (C)

We need to find the complementary strand for the given sequence. The complementary bases for each nucleotide in the given strand will be:
- T pairs with A
- A pairs with T
- C pairs with G
- C pairs with G
- A pairs with T
- T pairs with A
- C pairs with G
- C pairs with G
- A pairs with T
- A pairs with T
- T pairs with A

Therefore, the complementary strand (from 5' to 3') will be:
'5 ATG GTG AGG TAT TAA 3'.

3. **Count Purines in the Original Strand**:
Purines are adenine (A) and guanine (G). Now, we will count the number of purines in the original strand '3 TAC CAC TCC ATA ATT 5':
- T: 3
- A: 4
- C: 5
- G: 0

From the original strand, we have:
- Adenine (A): 4
- Guanine (G): 0

Total purines = 4 (A) + 0 (G) = 4.

4. **Count Purines in the Complementary Strand**:
Now let's count the purines in the complementary strand '5 ATG GTG AGG TAT TAA 3':
- A: 5
- G: 3

Total purines = 5 (A) + 3 (G) = 8.

5. **Final Count of Purines in the Watson-Crick Structure**:
The total number of purines in the Watson-Crick structure (both strands combined) is:
- Original strand purines: 4
- Complementary strand purines: 8
- Total purines = 4 + 8 = 12.

### Final Answer:
The total number of purines present in the Watson-Crick structure of this DNA is **12**.