Final answer:
A codon in mRNA consists of three nucleotides and it specifies one amino acid, with most amino acids having more than one codon that can encode them.
Step-by-step explanation:
A codon in a messenger RNA molecule consists of three nucleotides. Each mRNA codon specifies one amino acid. The genetic code is the set of instructions that determines how nucleotides are converted into the amino acid sequence of a protein.
With 64 possible mRNA codons, where most amino acids are encoded by more than one codon, this system provides the template for protein synthesis. For example, while codon AUG specifies the amino acid methionine and signals the start of protein synthesis, codons like GGU, GGC, GGA, and GGG all specify glycine.