Regulation of genes' expression.

Date: 2015-10-07; view: 498.

There are experimental evidence to show the genes do not operete tj produse structural peptides or fermentes aii the time. Each gene is normally more or less repressed (inactive). But, when a particular enzyme is needed, the relevant gene becomes derepressed (active) tj increase the production of the peptide (enzyme). Protein synthesis is controlled through regulation of gene action according to the need of the cell.

One of the mechanisms of gene activity regulation was described by French microbiologists Francois Jacob and Jacques Monod in 1961. The proposed mechanism was colled operon model. Operon model was described on E. coli. It was found that activity the three genes, which are nessesory to break down lactose to glucose, is regulated by a single operator switch.

The structural genes and operator genes, function as a unit, called operon.

The operator switch is turned on or off by a protein termed repressor, which is produced by a regulator gene.

The operon consists of three types of genes promoter, operator, and structural.

Promoter gene marks the site at which transcription of mRNA starts.

Operator gene controls the functioning of specific series of structural genes.

Structural genes (cistrons) produce mRNA, which in turn synthesizes a polipeptide on the ribosomes.

There are two systems of control the operon: inducible system and repressible system.

There is the description of inducible system. The repressor normally unites with the operator gene and turns it off. The enzyme RNA-polimerase can't move to structural genes, thus transcription and synthesis of specific protein stops. When an inducer (a substance whit needs enzymes to get metabolized) is present in the cytoplasm, the repressor substance joins with inducer, forming a repressor-inducer complex. The complex prevents the repressor from joining with the operator gene. This derepresses the structural genes. Hence, transcription and translation start, forming specific enzyme.

The operon is mechanism for regulation of prokaryotes genes activity. In the eukaryotic cells the regulation works through a complex network of regulatory genes.

The following points are notable about gene regulation in eukaryotes:

1. There are a lot of regulation factors on the level of tissue and organism.

2. The structural gene has coding and noncoding segments called exons and introns respectively. Thus there is regulation during splicing of exones.

3. Each structural gene has its own promoter gene.

4. There are sensor genes to pick up changes in the intracellular environment.

5. There are integrator genes to coordinate functions of structural genes located in different part of DNA.

6. The hyston proteins take part in the regulation of genes activity.

7. There is regulation while mRNA is passing through the nuclear membrane.