Genetic experiments showed that an amino acid is in fact encoded by a group of three bases, or codon.

How many bases are in a codon?

They showed that a short mRNA sequence—even a single codon (three bases)—could still bind to a ribosome, even if this short sequence was incapable of directing protein synthesis. The ribosome-bound codon could then base pair with a particular tRNA that carried the amino acid specified by the codon (Figure 2).

What bases make up a codon?

Codons are made up of any triplet combination of the four nitrogenous bases adenine (A), guanine (G), cytosine (C), or uracil (U). Of the 64 possible codon sequences, 61 specify the 20 amino acids that make up proteins and three are stop signals.