What is a codon a sequence of?

• A. A single nucleotide.
• B. Two nucleotides.
• C. Three nucleotides that code for a specific amino acid.
• D. Four nucleotides.

Answer: (C)

A codon is a unit of the genetic code consisting of three consecutive nucleotides in messenger RNA that specifies a particular amino acid to be added during protein synthesis. The ribosome reads mRNA in these fixed three-nucleotide chunks, so the code is read in triplets. With four possible nucleotides, there are 64 possible triplets, which map to amino acids (and some triplets serve as stop signals). This is why a codon is defined as three nucleotides that code for a specific amino acid. The other options don’t fit because one or two nucleotides aren’t enough to specify amino acids, and four nucleotides would alter the coding scheme entirely.