What is a codon?

What is a codon?

• A. A sequence of three amino acids
• B. A sequence of two nucleotides in mRNA
• C. A DNA triplet
• D. A sequence of three nucleotides in mRNA that codes for an amino acid

Answer: (D)

A codon is a three-nucleotide unit in messenger RNA that codes for a specific amino acid during protein synthesis. The ribosome reads mRNA in these triplets, and each codon matches with a corresponding tRNA carrying the appropriate amino acid, helping build the protein chain. Because codons are three nucleotides long, there are 64 possible codons, including ones that signal to start or stop translation. For example, the start codon AUG not only codes for methionine but also marks the beginning of the polypeptide, while the three stop codons tell the ribosome to finish. The other ideas don’t fit because a codon isn’t a sequence of three amino acids, which would form a short peptide instead of signaling which amino acid to add. It isn’t a DNA triplet either—codons refer to the three-nucleotide units in mRNA, whereas DNA triplets exist in the DNA template before transcription.

A codon is a three-nucleotide unit in messenger RNA that codes for a specific amino acid during protein synthesis. The ribosome reads mRNA in these triplets, and each codon matches with a corresponding tRNA carrying the appropriate amino acid, helping build the protein chain. Because codons are three nucleotides long, there are 64 possible codons, including ones that signal to start or stop translation. For example, the start codon AUG not only codes for methionine but also marks the beginning of the polypeptide, while the three stop codons tell the ribosome to finish.

The other ideas don’t fit because a codon isn’t a sequence of three amino acids, which would form a short peptide instead of signaling which amino acid to add. It isn’t a DNA triplet either—codons refer to the three-nucleotide units in mRNA, whereas DNA triplets exist in the DNA template before transcription.