Video Transcript
Which of the following nitrogenous bases is correctly paired? (A) Thymine forming a base pair with guanine. (B) Adenine forming a base pair with cytosine. (C) Guanine forming a base pair with thymine. Or (D) guanine forming a base pair with cytosine.
Nitrogenous bases, also known as nucleobases, are biological compounds containing
nitrogen atoms. There are four different nitrogenous bases in DNA: adenine, guanine, thymine, and
cytosine. Adenine and guanine have a fused ring structure derived from a purine. Thus, they are called purine bases. Cytosine and thymine have a single ring structure derived of pyrimidine. These bases are thus called pyrimidine bases. In DNA, the nitrogenous bases form purine–pyrimidine pairs by establishing hydrogen
bonds, two between adenine and thymine and three between cytosine and guanine.
Only option (D) proposes a correct pairing of nitrogenous bases. The nitrogenous base that is correctly paired is guanine forming a base pair with
cytosine.
