The manufacture of protein involves an elaborate system of molecules that must interact with one another in highly specific ways. There are vitally important start and stop signals that are different from the starts and stops in transcription. A lot of energy is invested in protein synthesis. The Genetic Code consists entirely of three-letter words composed of four bases. Clustering of codons that encode similar amino acids minimizes the biological effect of single-base substitutions.
Nonsense suppressor show how the genetic context can change the meaning of a given codon.
The Code is almost universal. Mutations can occur at different sites within a gene. The test to determine whether two mutations reside in the same gene is the trans complementation test. The complementation test provides the operational definition of a gene. Straight genetic experiments can reveal a lot about the molecular nature of the gene.