Why Regulate Gene Expression? Response to changing developmental or environmental conditions Save… time time energy energy raw materials raw materials
Prokaryotic Regulation Feedback Inhibition Product inhibits enzyme function Product inhibits enzyme function Regulation of transcription Product inhibits enzyme production Product inhibits enzyme production
Drug Company Research and Development DevelopmentDistributionDistributionTestingTestingProductionProductionMGMTMGMT
Operon Regulation Inducible Default off Repressor active Repressor active Turned on when substrate is present Repressor inactive Repressor inactive Repressible Default on Repressor inactive Repressor inactive Turned off when product is present Repressor active Repressor active
Inducible Operon Default: OFF 123PORG RNA Poly Substrate Absent Repressor protein binds to operator Operon blocked No substrate-catabolizing enzymes produced Substrate Present Substrate inactivates repressor protein Operon transcribed Enzymes produced
Lac Operon
Trp Operon
Repressible Operon Default: ON 123PORG RNA Poly Product Absent Repressor protein inactive Operon transcribed Product-anabolizing enzymes produced Product Present Product activates repressor protein Operon blocked No enzymes produced
Inducible, Repressible, Both, or Neither? 1.The Lac operon 2.Regulatory gene codes for repressor protein 3.Operon expressed (ON) by default 4.Substrate inactivates repressor protein 5.Product binds to RNA polymerase 6.Product activates repressor protein 7.Repressor protein status changes when bound by particles 8.Enzymes deactivate repressor protein 9.The Trp operon 10.Operon blocked (OFF) by default 11.Active repressor protein blocks transcription 12.Repressor is created in an active state
Inducible, Repressible, Both, or Neither? 1.The Lac operonI 2.Regulatory gene codes for repressor proteinB 3.Operon expressed (ON) by defaultR 4.Substrate inactivates repressor proteinI 5.Product binds to RNA polymeraseN 6.Product activates repressor proteinR 7.Repressor protein status changes when bound by particlesB 8.Enzymes deactivate repressor proteinN 9.The Trp operonR 10.Operon blocked (OFF) by defaultI 11.Active repressor protein blocks transcriptionB 12.Repressor is created in an active stateI
Tend to have 10x the genes of prokaryotes Expression is controlled at multiple points Eukaryotic Regulation
Chromatin Modification Euchromatin Heterochromatin
Chromatin Modification Methylation Attachment of methyl groups to cytosine Attachment of methyl groups to cytosine Histone Acetylation Attachment of acetyl groups to histones Attachment of acetyl groups to histones Loosens grip of histones on DNA Loosens grip of histones on DNA
Alternative Splicing
Post-transcriptional Regulation Protein Degradation
Review Questions Use no more than 1 word for each answer. 1.What type of organic molecule is a histone? 2.What is the structural difference between heterochromatin and euchromatin? 3.What does a proteasome do?