Question

(3) Which of the following statements is incorrect?
[A]A, G, C and T bases are present in DNA.
[B]A and T are joined together by two hydrogen bonds in DNA
[C] A and C are purine bases
[D] T and U are pyrimidine bases.​

Answer 1

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The nitrogenous bases present in nucleic acids are A, G, C, T/U.

• A = Adenine
• G = Guanine
• C = Cytosine
• T = Thymine
• U = Uracil

Thymine (T) is found in DNA and Uracil (U) is found in RNA. They pair with each other by hydrogen bonds like:

• A and T joined together by two Hydrogen bonds.
• C and G by three hydrogen bonds.

Here, A and G are known to be larger purines whereas C and T/U are smaller pyrimidines depending upon the nucleic acid DNA or RNA.

Hence,

Ans - Option C✓ is the incorrect choice because C is not a purine, it is a pyrimidine.

Other choices are satisfying all the concepts about the structure of purines and pyrimidines in DNA or RNA.

Answer 2

The nitrogenous bases present in nucleic acids are A, G, C, T/U.

A = Adenine

G = Guanine

C = Cytosine

T = Thymine

U = Uracil

Thymine (T) is found in DNA and Uracil (U) is found in RNA. They pair with each other by hydrogen bonds like:

A and T joined together by two Hydrogen bonds.

C and G by three hydrogen bonds.

Here, A and G are known to be larger purines whereas C and T/U are smaller pyrimidines depending upon the nucleic acid DNA or RNA.

Hence,

Ans - Option C✓ is the incorrect choice because C is not a purine, it is a pyrimidine.

Other choices are satisfying all the concepts about the structure of purines and pyrimidines in DNA or RNA.