a) Operon: An operon is a cluster of genes that are transcribed together to give a single messenger RNA (mRNA) molecule, which therefore encodes multiple proteins.

b) Cistron: Refers to a section of a DNA or RNA molecule that codes for a specific polypeptide in protein synthesis.

c) Operator gene: An operator is a genetic sequence which allows proteins responsible for transcription to attach to the DNA sequence.

d) Promoter gene: Provides the binding site for the RNA polymerase.