How many nitrogenous bases form a codon?

How many nitrogenous bases form a codon?

• A. 1
• B. 2
• C. 3
• D. 4

Answer: (C)

In the genetic code, a codon is read as a triplet of nucleotides in mRNA. That means three nitrogenous bases come together to specify one amino acid (or a stop signal). The reason for this three-base length is combinatorial: a single base yields only 4 possibilities, two bases yield 4 × 4 = 16 possibilities—still not enough to uniquely encode all 20 amino acids plus stop signals. Three bases give 4 × 4 × 4 = 64 possible codons, which is more than enough to cover all amino acids and the stop signals. In RNA, those bases are adenine, uracil, cytosine, and guanine, so one codon consists of three of these bases.

In the genetic code, a codon is read as a triplet of nucleotides in mRNA. That means three nitrogenous bases come together to specify one amino acid (or a stop signal). The reason for this three-base length is combinatorial: a single base yields only 4 possibilities, two bases yield 4 × 4 = 16 possibilities—still not enough to uniquely encode all 20 amino acids plus stop signals. Three bases give 4 × 4 × 4 = 64 possible codons, which is more than enough to cover all amino acids and the stop signals. In RNA, those bases are adenine, uracil, cytosine, and guanine, so one codon consists of three of these bases.