The genes are switched and switched off at different times. This differential gene action is also responsible for the synthesis of different types of proteins (enzymes) at different times.
Not all enzymes are required at all times. Enzymes required during early stages of development may not be required at later stages in the life cycle and vice versa. The metabolic products produced may induce or repress the enzyme synthesis.
Genetic control on protein synthesis is exercised at three stages – transcription stage, translation stage and at the release of polypeptide chain (post translation stage).
The control mechanism ensures that the cell is not unnecessarily flooded by the enzymes which are required only at particular times and only in particular quantity.
Depending on the requirement the enzyme synthesis can either be induced or suppressed. Genetic regulation is seen both in prokaryotes and in eukaryotes.
While the purpose of genetic regulation is same in both prokaryotes and eukaryotes, the mechanisms differ.
In prokaryotes, the mechanism of genetic regulation is simple when compared with the eukaryotic organisms the reasons for this are not far to understand.
As the eukaryotic organisms are far more complex they do require a very sophisticated mechanism of genetic regulation.