How many codons are present in the genetic code, and what do they specify?

• A. 64 codons code for 20 amino acids plus stop signals
• B. 61 codons code for amino acids; 3 are stop
• C. 32 codons code for 16 amino acids
• D. 50 codons code for amino acids and stop signals

Answer: (C)

Codons are triplets of nucleotides that carry the genetic message. Each triplet can specify one of the 20 amino acids or signal the end of translation.

Since codons are three nucleotides long and there are four nucleotides available, there are 4^3 = 64 possible codons in total. Of these, 61 codons code for amino acids, providing redundancy so that multiple codons can encode the same amino acid. The remaining three codons are stop signals that tell the ribosome to terminate protein synthesis.

This setup—64 total codons, with 61 specifying amino acids and 3 signaling stops—explains how the genetic code maps nucleotide triplets to the building blocks of proteins.