Question

A \(340\ \text{Å}\) long segment of DNA molecule has \(40\) thymine nitrogenous bases, what will be the number of guanine bases in the same segment?

• A. \(10\)
• B. \(20\)
• C. \(40\)
• D. \(60\)

Hint:

Find the number of base pairs from the length, then use Chargaff's rule A = T and G = C.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
In B-DNA, successive base pairs are \(3.4\ \text{Å}\) apart. Chargaff's rule says A = T and G = C.

Step 2: Total bases
Number of base pairs = \(\dfrac{340}{3.4} = 100\).
Total bases = \(2 \times 100 = 200\).

Step 3: Calculation
T = 40, so A = 40 and A + T = 80.
G + C = \(200 - 80 = 120\).
Since G = C, G = \(\dfrac{120}{2} = 60\).

Final Answer:
The segment has 60 guanine bases. \[ \boxed{\text{(D) }60} \]