Regulation in lac operon

INTRODUCTION TO LAC OPERON , REGULATION , TYPES OF REGULATIONS , AND BRIEF COMPARISON BETWEEN THE TYPES

1. Regulation in lac operon Presented by:- Swati Suman Enrollment no.:- A35204418013

2. INTRODUCTION LAC OPERON The  lac  operon is an  operon , or group of genes with a single promoter . The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source . The   lac   operon  is a cluster of three structural genes encoding proteins involved in lactose metabolism and the sites on the DNA involved in regulation of the operon. The three genes are: ( 1)  lacZ , which encodes the enzyme  β- galactosidase (2)  lacY , which encodes lactose permease (3)  lacA , which encodes a lactose  transacetylase .

3. Regulation The activity of the promoter that controls the expression of the  lac operon is regulated  by two different proteins ie . Lac repressor and CAP( Catabolite Activator Protein). One of the proteins prevents the RNA polymerase from transcribing (negative control), the other enhances the binding of RNA polymerase to the promoter (positive control).

4. Types of regulation There are basically 2 types of regulation in lac operon:- 1. Negative regulation -occurs when binding of a protein prevents an event. 2. Positive regulation- occurs when binding of the protein causes a event.

5. Negative regulation The protein that inhibits transcription of the  lac  operon is a tetramer with four identical subunits called  lac  repressor. The lac repressor binds to the operator. The DNA sequence covered by the repressor overlaps the DNA sequence recognized by the RNA polymerase. Therefor , when the repressor is bound to the operator , RNA polymerase cannot bind to the promoter and transcription can not occur ,the lac operon is said to be under negative control

6. Process of negative regulation

7. Positive regulation When the expression of genetic information is quantitatively increased by the presence of specific regulator elements, it is called positive regulation. Catabolite represion is a type of positive control in the lac operon.

8. The catabolite activator protein (CAP) ,complex cAMP , binds to a site near the promoter and stimulates the binding of RNA polymerase. The cellular level of cAMP are controlled by glucose ; allolactise level increase the abundance of cAMP and enhance the transcription of the abundance of cAMP and enhance the transcription of the lac structural gene.

9. Positive vs negative regulation

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