Question

Q.131. A 340 $\stackrel{o}{A}$ long segment of DNA molecule has 20 thymine nitrogenous bases, what will be the number of guanine nitrogen bases in the same segment?
A) 10
B) 40
C) 80
D) 160

Answer 1

Dear student,
Answer is option B.
One turn of DNA is 3.4 nm (34 angstrom) long and have 10 base pairs. So, 340 angstrom long DNA segment would have 100 base pairs (10 x 10).
Given that number of thymine bases in this segment= 20
Since thymine pairs with adenine in a double stranded DNA, so total number of thymine bases = number of adenine bases.
Hence, total number of adenine bases in given DNA strand = 20.
So total number of AT base pairs in given DNA= 20
Number of GC pairs in given DNA = total base pairs - total number of AT pairs
= 100- 20 = 80.
Since total number of GC pairs in given DNA is 80; so total number of guanine bases in the same segment = 80/2 = 40.
Regards.