The statement "When levels of the amino acid are high, it binds to the repressor, allowing synthesis of this amino acid to proceed" (A).
E. coli needs amino acids to survive. It can ingest the amino acid, Tryptophan from the environment. When the levels of Tryptophan are low, it can synthesize Tryptophan by using enzymes that are encoded in five genes. These genes lie next to each other in the tryptophan operon. If tryptophan is available in the environment, E. coli will not synthesize it.
