4.6 Regulation of gene expression:

It is the multistep process by which a gene is regulated and its product is synthesized. Thus, gene expression results in the formation of a Polypeptide.

Gene expression process is regulated at different levels.

In eukaryotes, the regulation can be at different levels like-

1. Transcriptional level (formation of primary transcript)

2. Processing level ( regulation of splicing)

3. Transport of m-RNA from nucleus to the cytoplasm.

4. Translational level.

 

Genes of a cell are expressed to perform different functions. For eg. An enzyme beta galactosidase is synthesised by E. coli. It is used for hydrolysis of lactose into galactose and glucose.

If E. coli bacteria do not have lactose in the surrounding medium as a source of energy, then enzyme b-galactosidase is not synthesised.

So, it is the metabolic or physiological or environmental conditions that regulate expression of genes.

The development and differentiation of embryo into an adult organism, is also a result of the coordinated regulation or expression, of several sets of genes.

Now one has to understand and know the mechanism by which the organisms regulate gene expression in response to changes in the environment. If so, whether single mechanism exists for regulation of the expression of different genes/ sets of genes or different genes are regulated by different mechanisms.

Certain bacteria like E. coli adapt to their chemical environment by synthesizing certain enzymes depending upon the substrate present. Such adaptive enzyme is called inducible enzymes.

A set of genes will be switched on when there is necessity to metabolise a new substrate. This phenomenon is called induction and small molecule responsible for this, is known as inducer. It is positive control.