Regulating gene expression
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Regulating gene expression

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  • Allolactose = isomer of lactose, inactivates the repressor P lease O ffer Z ach Y our A pple
  • Allolactose = isomer of lactose, inactivates the repressor P lease O ffer Z ach Y our A pple
  • Repressor
  • Repressor
  • Repressor
  • Repressor
  • Repressor

Regulating gene expression Presentation Transcript

  • 1. Regulation of Gene ExpressionLac and Trp Operon
  • 2. Levels of Metabolic Control The amount of cellular products can be controlled by regulating:  Enzyme activity: alters protein function  Transcription: affects whether a gene is turned on or off
  • 3. Example:E. coli in human intestine No tryptophan present, needs to synthesize Tryptophan present, does not need to synthesize Feedback inhibition on the production of trp
  • 4. Levels of Metabolic Control Protein function level: adjust activity of enzymes already present Short term, quick onset regulation
  • 5. Levels of Metabolic Control Transcription level: control the expression of genes which affects number of enzymes produced Long term, slow onset regulation
  • 6. Gene Expression Types of Definition Type of genes expression Constitutive Genes are Housekeeping genes(unregulated) always ON (regulatory genes) Genes are Inducible only turned Structural genes (regulated) on as needed Genes are Repressible only turned Structural genes (regulated) off as needed
  • 7. Gene Expression Would anabolic pathways have genes that are inducible or repressible? Would catabolic pathways have genes that are inducible or repressible?
  • 8. Anabolic Pathway: Repressible Anabolism: synthesis of molecules from simpler subunits If an essential nutrient is not present in the environment, bacteria must be able to synthesize the nutrient on its own However, bacteria do not need to produce the essential nutrient if it is already present in the environment
  • 9. Catabolic Pathway: Inducible Catabolism: breakdown of complex molecules into simpler units It would be a waste of energy for bacteria to make enzymes for the breakdown of a substance if that substance does not exist do not need to catabolize molecules that are not present in its cellular environment
  • 10. Gene ExpressionPathway Anabolic CatabolicProduct of Synthesis of Breakdown ofgenes nutrient nutrientExpression Repressible Inducible Gene will turn off Gene turned on when nutrient is when nutrient present in the being brokenExplanation environment. down is present. Thus no need to synthesize it.
  • 11. Examples Classify the metabolic pathway: catabolic or anabolic Classify the gene expression: inducible or repressible Lac Operon Polypeptides that make up enzymes for lactose hydrolysis and uptake Trp Operon
  • 12. Operon A group of genes that share a single promoter Genes code for proteins that have related functions Promoter Final product is tryptophan
  • 13. Structural Genes: trp operon Structural Genes 5 genes making 5 polypeptides that combine to make 3 enzymes Enzymes participate in a sequence of steps to make tryptophan (trp) an amino acid Fig. 18.20a
  • 14. Operon Components Promoter  Region on DNA where RNAP binds to start transcription  acts as the on/off switch for genes Operator  region on DNA that controls access of RNAP to the genes  Can activate or repress transcription Structural genes  Genes to be transcribed by RNAP
  • 15. Operon Regulation: trp operon trp operon Promoter Structural Genes Regulatory Operator Final product is tryptophan Gene Fig. 18.20a
  • 16. Operon Regulation Regulatory gene  region on DNA that codes for the production of the regulatory protein  upstream of the operon  constitutive expression: transcribed continuously Regulatory protein  Binds to operator and blocks attachment of RNAP  Allosteric: alternates between active and inactive forms
  • 17. trp operon Regulation Transcription  Regulatory gene: trpR Translation  Allosteric regulatory protein Active or inactive?  has 2 forms: active or inactive Fig. 18.20a
  • 18. trp operon Regulation  Which form is the regulatory protein made as, active or inactive?  Recall: the active regulatory Active or inactive? protein will bind to the operator which blocks RNAP transcription  Hint: trp operon produces tryptophan, an amino acid essential to its survival Fig. 18.20a
  • 19. Regulatory Gene: trpR Codes for an trp repressor protein Constitutively expressed in its inactive form
  • 20. trp operon Regulation  In what type of environmental condition would the bacteria Inactive want to switch the regulatory protein (trpR) from the inactive to the active form?  In other words, why would the cell want to turn off transcription of these genes? Fig. 18.20a
  • 21. trp operon Regulation  How do you switch from the inactive form of the Inactive regulatory protein to the active form?  How do you turn on the regulatory protein? Fig. 18.20a
  • 22. Effector any molecule that can regulate the activity of a protein Corepressor:  activates the repressor  causing regulatory protein to bind to the operator  inactivates gene expression Inducer:  inactivates the repressor  prevents regulatory protein from binding to the operator  activates gene expression
  • 23. trp operon Regulation  What effect will the effector have on the regulatory protein? Inactive  What effect will the effector have on gene expression of the trp operon?  Is the effector a corepressor or inducer? Fig. 18.20a
  • 24. Effector: Corepressor Hint: negative feedback  What molecule do you think is a logical choice to act as a corepressor in the trp operon? Fig. 18.20b
  • 25. trp operon Regulation Effector molecule: tryptophan (trp)  Corepressor Regulatory protein: trp repressor  Made inactive, RNAP can transcribe, trp made  Activated by trp (corepressor) Active trp repressor binds to operator  Prevents RNAP from transcribing genes  Stops trp production
  • 26. Repressible operon Gene is normally “on” Transcription is inhibited when a molecule binds allosterically to a regulatory protein Negative feedback / feedback inhibition Anabolic pathways Example: Trp operon is turned off when tryptophan (corepressor) binds to repressor
  • 27. trp operon animationAnimation http://highered.mcgraw-hill.com/olc/dl/120080/bi http://www.as.wvu.edu/~dray/219files/TrpAttenu (ignore information on attenuation)Tutorial http://bcs.whfreeman.com/thelifewire/content/ch
  • 28. Models of Negative Regulation Repressible Operon (e.g. trp)  Repressor made in inactive form  activated by corepressor  Turns gene off Inducible Operon (e.g. lac)  Repressor made in active form  inactivated by inducer  Turns gene on
  • 29. lac operon Recall: Lactose = glucose + galactose
  • 30. lac operon Simulation WebSite:  Spongelab.com  Explore  Biology  Games and Simulation  “Gene Machine: The Lac Operon”
  • 31. Components: lac operon lac operon Promoter Structural Genes Regulatory Operator Gene Hydrolyze Lactose Adds acetyl lactose into transporter group to glucose and (into cell) galactose galactosePlease Offer Zach Your Apple Fig. 18.21
  • 32. Structural Genes: lac operon codes for 3 enzymes β-galactosidase (lacZ gene): lactose hydrolysis into glucose and galactose permease (lacY gene): membrane protein that transports lactose into the cell transacetylase (lacA gene): adds acetyl group to galactose (significance in lactose metabolism unclear)
  • 33. lac operon Regulation lac operon Promoter Structural Genes Regulatory Operator GenePlease Offer Zach Your Apple Fig. 18.21
  • 34. lac operon RegulationTranscription  Regulatory gene: LacI  Allosteric regulatory protein Translation  has 2 forms: active or inactive Active or inactive? Fig. 18.21a
  • 35. lac operon Regulation  Which form is the regulatory protein made as, active or inactive?  Recall: the active regulatory Active or protein will bind to the operator inactive? which blocks RNAP transcription  Hint: lac operon produces enzymes that breakdown lactose Fig. 18.21a
  • 36. Regulatory Gene: LacI Codes for an active lac repressor protein which binds to the operator Constitutive expression of the active form
  • 37. lac operon Regulation RNAP  In what type of environmental condition would the bacteria want to switch the regulatory Active protein (lacI) from the active to the inactive form?  In other words, why would the cell want to turn on transcription of these genes? Fig. 18.21a
  • 38. lac operon Regulation RNAP  What type of effector do you need to turn off the regulatory protein: corepressor or inducer? Active  What effect will the effector have on the on gene expression of the lac operon? Fig. 18.21a
  • 39. lac operon Regulation RNAP  What molecule would be an appropriate inducer for the lac operon? Fig. 18.21a
  • 40. lac operon Regulation Effector molecule: allolactose  An isomer of lactose  An inducer allolactose binds to regulatory protein (lac repressor)  Inactivates lac repressor preventing it from binding to the operator  Allows RNA polymerase to transcribe genes  Produces enzyme β-galactosidase which hydrolyzes lactose
  • 41. lac operon Regulation E. Coli cells mainly use glucose as a source of energy When living in a system with lactose, bacteria can hydrolyze lactose to produce glucose The lac operon is only turned on when lactose is present
  • 42. Inducible operon Gene normally “off” Transcription is stimulated when a molecule binds allosterically to a regulatory protein Proteins made “on demand” Catabolic pathway (breakdown substances) Example: Lac operon turned on when allolactose (inducer) binds to repressor
  • 43. lac operon animationAnimation http://www.youtube.com/watch?v=oBwtxdI1zvk&featur http://vcell.ndsu.nodak.edu/animations/lacOperon/movi http:// www.dartmouth.edu/~cbbc/courses/movies/LacOperon. (a little low tech)Tutorial http://bcs.whfreeman.com/thelifewire/content/chp13/130 http://www.sumanasinc.com/webcontent/animations/co (looks the same as above)
  • 44. Negative Gene Regulation Operons are switched off by the active form of the regulatory protein (repressor)  Trp operon: repressor activated by corepressor, binds to operator  Lac operon: repressor made in active form, binds to operator
  • 45. Overview of Gene Regulation Gene Regulation Negative Gene Regulation Positive Gene Regulation (e.g. allolactose on lac operon) (e.g. cAMP on lac operon) An active regulatory protein An active regulatory protein turns gene expression OFF turns gene expression ON (repressed) (activated)Repressible Operon (e.g. trp) Inducible Operon (e.g. lac)Has the ability to be turned Has the ability to be turned ONOFF by a corepressor by an inducerGene expression normally ON Gene expression normally OFF
  • 46. Positive Gene Regulation Active form of the regulatory protein turns on or increases the transcription of the operon Animation of positive and negative regulation of the lac operon: http://highered.mcgraw-hill.com/olc/dl/120080/bi