Question

During analysis of the DNA of an organism having 5386 nucleotides find out $A=29\%$, $G=17\%$, $C=32\%$, $T=17\%$. Considering the Chargaff’s rule it can be concluded that

• A. It is single stranded DNA
• B. Both A and B
• C. It is double stranded circular DNA
• D. It is double stranded linear DNA

Answer 1

The correct option is A It is single stranded DNA

Introduction to Chargaff’s rule
According to the Chargaff rule, the ratio of purines and pyrimidines remains constant and equal in DNA, that is A+G = T+ C.

In addition to that, the percentage of adenine (A) is equal to the percentage of thymine (T) and the percentage of guanine (G) is equal to the percentage of cytosine (C) in double stranded DNA, that is A = T; G = C.
Double stranded, circular or linear DNA
According to the Chargaff’s rule, A+G = T+ C.
In the above question it is given that,$A=29\%$, $G=17\%$, $C=32\%$, $T=17\%$.
$29\%+17\%$ is not equal to $32\%+17\%$, that is $46\%$ is not equal to $49\%$.

In addition to this Adenine is not equal to Thymine, similarly, Guanine is not equal to Cytosine. Here $A\ne$T and $G\ne C$.

Therefore, it is not a double stranded circular DNA and double stranded linear DNA.
Single stranded DNA
The Chargaff’s rule is not applicable to single stranded DNA. It has a different proportion of purines and pyrimidines. Thus, the given is a single stranded DNA as it does not follow the Chargaff’s rule.

Final answer
(C) It is single stranded DNA