Regulation-of-gene-expression-operon-concept

• Gene expression refers to the multistep process that ultimately results in the production of a functional gene product, either ribonucleic acid (RNA) or protein.

REGULATION OF GENE EXPRESSION comprises.

                 i) Transcription
                 ii) Charging of IRNA (activation of amino acids)
                 iii) Translation
                 iv) Post-translational modifications.

• Gene is expressed in terms of the synthesis of protein.
• Transcription is the primary site of regulation in both prokaryotes and eukaryotes.
• Regulation of transcription is controlled by a regulatory sequence of DNA, usually embedded in the non-coding region of the genome.
• Cis-acting factors influence the expression of genes only on the same chromosome while trans-acting factors influence gene on other chromosomes.
• the expression of a gene is increased by the presence of a specific regulator, called activator or inducer or enhancer is called positive regulations.
• In prokaryotes, the genes involved in a metabolic pathway are often present in a linear fashion, called an operon. for eg- Lactose operon (Lac operon for regulating lactose metabolism).
• other examples are Arabinose operon (Ara operon for arabinose metabolism). Galactose operon (Gal operon for galactose metabolism).
• Operon contains an operator, a  segment of DNA that regulates the activity of the structural genes of the operon.

Lactose  operon  or  Lac operon

• Comprises of three structural genes coding for 3 proteins.
• Lac z-Beta galactosidase, Lac y-Permease-a carrier protein that helps permeation of lactose to cell and Lac-a-Thiogalactoside Transacetylase.
• CAP is a Positive  Regulator of  Lac  Operon, which is complexed with cAMP that facilitates binding of RNA Polymerase to the promoter.
• Whenever Glucose is present irrespective of the presence or absence of lactose, the lac operon is switched off.’
• Whenever Glucose is absent lac operon is on.
• When Both Glucose and Lactose Absent, CAP inactive as cAMP Hence, a structural gene not transcribed and there is Repression of Lac Operon.
• In operator, site (O)  Repressor binds to this site and blocks transcription.
  

   

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