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Lac operon overall
- 2. Synopsis Introduction to operon Operonin prokaryotes Structural of operon Structural genes - lac operon Functional genes - lac operon Absence & presence of lactose Lac operon Absence & presence of glucose CRP and cAMP
- 3. A bacterial celllives in direct contact with its environment, which may change dramatically in chemical composition from one moment to the next. At certain times, a particular compound may be present, while at other times that compound is absent. A number of strategies an organism use to regulate expression of individual genes. By controlling transcription initiation, a cell can regulate which proteins it produces and how rapidly. Introduction - Operon
- 4. Define Operon Anoperon is a group of genes that are transcribed at the same time. They usually control an important biochemical process. They are only found in prokaryotes.
- 5. The Bacterial Operon:- Inbacteria, the genes that encode the enzymes of a metabolic pathway are usually clustered together on the chromosome in a functional complex called an operon. A typical bacterial operon consists of:- Structural genes Promoter Operator Regulatory
- 7. Lac Operon Itis the Inducible operon since the presence of lactose the induce the operon to switch on. The lac operon consists of three genes each involved in processing the sugar lactose. One of them is the gene for the enzyme β- galactosidase. This enzyme hydrolyses lactose into glucose and galactose. The lac operon - the cluster of genes that regulates production of the enzymes needed to degrade lactose in Escherichia coli and some other enteric bacteria
- 8. Lactose isa disaccharide composed of galactose and glucose. In its natural environment, the lac operon allows for the effective digestion of lactose. It achieves this with the lac repressor which halts the production in the absence of lactose. The Catabolite activator protein(CAP), which assists in production in the absence of glucose.
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- 10. Lac Operon Repressor PromoterOperator Lac Z Lac Y Lac A β-galactosidase Lactose permease transacetylase RNA polymerase
- 11. Operator binding sitefor repressor Promoter Binding site for RNA polymerase Repressor Gene encoding for the repressor protein. Binds to DNA at the operator site and blocks the transcription Lac I controls the production of repressor protein Functional genes
- 12. Gene Codes forenzyme Function of the enzyme Lac Z β-galactosidase Breaks down lactose into glucose & galactose. Lac Y galactose permease This protein, found in the E.coli cytoplasmic membrane, actively transports lactose into the cells. Lac A Thio-galactoside trans acetylase The function of this enzyme is not known. Structural genes
- 13. Carbohydrates Activator protein Repressor protein RNA polymerase Lac operon + GLUCOSE +LACTOSE Not bound to DNA Lifted off operator site Keeps falling off promoter site No transcription + GLUCOSE - LACTOSE Not bound to DNA Bound to operator site Blocked by the repressor No transcription - GLUCOSE - LACTOSE Bound to DNA Bound to operator site Blocked by the repressor No transcription - GLUCOSE + LACTOSE Bound to DNA Lifted off operator site Sits on the promotor site Transcription
- 14. Presence of lactose Therepressor gene produces repressor, in the presence of lactose it binds to the repressor. This will not blocks the action of RNA polymerase, then the transcription may proceed and the enzyme will be synthesized.
- 15. Lac Operon Repressor PromoterOperator Lac Z Lac Y Lac A β-galactosidase Lactose permease transacetylase RNA polymerase Lactose Repressor protein M RNA
- 16. Absence of lactose Therepressor gene produces repressor, which binds to the operator. This blocks the action of RNA polymerase, thereby preventing transcription.
- 17. Lac Operon Repressor PromoterOperator Lac Z Lac Y Lac A RNA polymerase Repressor protein M RNA No transcription
- 18. Presence of glucose Therepressor gene produces repressor, in the presence of glucose which the repressor binds to the operator. This will also blocks the action of RNA polymerase, there by preventing transcription.
- 19. Lac Operon Repressor PromoterOperator Lac Z Lac Y Lac A RNA polymerase Repressor protein M RNA No transcription Glucose
- 20. Absence of glucose Therepressor gene produces repressor, which binds to the operator. This blocks the action of RNA polymerase, thereby preventing transcription.
- 21. Lac Operon Repressor PromoterOperator Lac Z Lac Y Lac A RNA polymerase Repressor protein M RNA No transcription
- 22. In condition oflow glucose CRP and cAMP will induces the RNA polymerase to transcript the DNA for the enzymes / proteins CRP cAMP
- 23. Lac Operon CRP binding site PromoterOperator Lac Z Lac Y Lac A β-galactosidase Lactose permease transacetylase RNA polymerase
- 24. CONCLUSION Lac operon isa cluster of gene that regulate lactose metabolism. It is an inducible operon. Lac operon is transcribed only when lactose is single source of energy, in order to conserve cellular resource and energy by not producing the enzyme, when there is no need to metabolize lactose.