What is a codon?

• A. A sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid
• B. A protein that speeds chemical reactions
• C. A chromosome segment
• D. A gene promoter

Answer: (A)

A codon is a three-nucleotide unit that carries the genetic information to specify a particular amino acid during protein synthesis. In DNA or RNA, these three bases form a codon, and each codon matches to one amino acid in the genetic code. The ribosome reads codons in the mRNA, and transfer RNAs bring the corresponding amino acids to build the protein chain. Some codons act as signals to start or stop translation, but the essential idea is that a codon encodes one amino acid. That’s why the description that a codon is a sequence of three adjacent bases on DNA or RNA providing genetic code information for a specific amino acid best captures what a codon is.