Question

Adenine is 30%, what would be the percentage of guanine?
A. 10%
B. 20%
C. 30%
D. 40%

Answer 1

Hint: J. D. Watson and Francis H. C. Crick proposed a model of DNA structure as a double helix form. They inferred that in each DNA molecule there are two long and parallel nucleotide chains helically coiled around the same axis.

Complete answer:
DNA is a macromolecule, polymers of nucleotides, linear, spirally coiled in eukaryotes and circular in prokaryotes. It controls the structure and function of cells through transcription and translation.
DNA is found in all living cells except mature mammalian RBC and sieve tubes. It is found in chromatin of nucleus in eukaryotes, nucleoid, and plasmid of prokaryotes (as circular strand) mitochondria, and plastids.
The right handed helices are held together by their bases which are paired together by covalent hydrogen bonds. There are ten base pairs per turn of the double helix. Two helices are coiled in such a way that they cannot be separated without unwinding.
The two chains of a helix are of opposite polarity i.e. anti-parallel 3’-5’ and 5’-3’ in direction.
A large size purine comes opposite a small sized pyrimidine which generates uniform distance between the two strands of helix. The four types of bases in DNA are Adenine (A), Thymine (T), Guanine (G) and Cytosine(C).
Chargaff’s rule states that the amount of Purines in a DNA is always equal to the amount of pyrimidines. This is also known as the base equivalence rule. It also states that molal concentration of A is equal to C and G is equal to C.

Note:
So as per the question, A= 30%, therefore T=30% (as A=T)
Now, A+ T+ G+ C = 100%
30% + 30% + G + C= 100%
G + C= 40%
And G= C = 20%