In order to create a particular protein the gene must be turned on via binding of the enzyme RNA polymerase to the promoter of the gene. When a gene is in the "on" state (i.e., it is active), two processes occur one after the other:

• transcription: the information in the gene (codons) is transcribed into a messenger RNA (mRNA);
• translation: the mRNA is translated into amino acids (the building blocks of a protein)

This two-step process is referred to as the central dogma of molecular biology.

In addition to the promoter a gene has one or more regulatory sequences which are capable of binding a regulatory protein that affects the degree of transcription of the gene (positively or negatively). Also, the produced protein may act as a regulatory protein of its encoding gene.

Because there is no direct process from gene to protein, but a chain of biochemical processes must take place, there occurs a "delay" in the reaction. As we shall see, this can lead to variations in the concentrations of biochemical substances involved.