Which codons are given as coding for glycine?

• A. CCC and CCT
• B. CCC and CCG
• C. CCT and CCC
• D. CCC and CAA

Answer: (A)

Codons are the three-nucleotide messages that specify which amino acid to add during protein synthesis. Glycine is encoded by four codons that start with G: in RNA they are GGU, GGC, GGA, GGG; in the DNA/coding sense this corresponds to GGT, GGC, GGA, GGG (T instead of U).

The sequences listed are all made of C and T (in DNA form): CCC and CCT, for example, are proline codons (in RNA they appear as CCC and CCU, which code for proline). Since glycine’s codons begin with G, these options do not code for glycine. That means the question as written doesn’t provide glycine codons among the choices; the correct glycine codons are GGT/GGC/GGA/GGG in DNA (or GGU/GGC/GGA/GGG in RNA).