Signal molecular be needed for both types Add signal mol.-Operon on (inducible operon) Inducer(诱导物) Add signal mol.-Operon off (repressible operon) Co-repressor((辅阻遏物)
Signal molecular be needed for both types Add signal mol. → Operon on Add signal mol. → Operon off Co-repressor(辅阻遏物) Inducer(诱导物) (inducible operon) (repressible operon)
Operon control model NEGATIVE CONTROL POSITIVE CONTROL RNA polymerase Inducible Inactive Inactive Active Repressor represso activator activator active Inducer Inducer brake >REPRESSED> INDUCED accelerator REPRESSED> INOUCED Repressible Inactve Active Active repressor activator activator Corepressor Corepressor >INDUCED REPRESSED INDUCED >REPRESSED
brake accelerator active Inducible Repressible Operon control model
2.Negative Control of the lac Operon (a)No lactose;repression regulatory gene Operator lacl lacZ lacY lacA Promoter mRNA the operon is off,or repressed Repressor monomer Tetramer When the repressor occupies the operator,it appears to prevent RNA polymerase from binding to the promoter and transcribing the operon
2. Negative Control of the lac Operon When the repressor occupies the operator, it appears to prevent RNA polymerase from binding to the promoter and transcribing the operon regulatory gene the operon is off, or repressed
Negative Control of the lac Operon (b)+lactose;derepression Transcription Inducer B-Galactosidase Permease Transacetylase Allosteric(变构)protein: binding of inducer to the the protein change protein changes the conformation and dissociate shape of a remote site on the protein and alters its from the operator thus interaction with operator inducing the operon What is the nature of this inducer?
Negative Control of the lac Operon Allosteric(变构)protein: binding of inducer to the protein changes the shape of a remote site on the protein and alters its interaction with operator the protein change conformation and dissociate from the operator thus inducing the operon What is the nature of this inducer?
Actual inducer:allolactose(异乳糖) an alternative form of lactose Production of inducer CopyrightThe McGraw-Hill Companies,Inc.Permission required for reproduction or display. CH2OH CH2OH CH>OH B-galactosidase OH Lactose (β-1,4 linkage) Allolactose (β-1,6 linkage) No permease and B-galactosidase How can lactose be metabolized to allolactose? Repression is somewhat leaky:a low basal level of the lac operon products is always present
Production of inducer Actual inducer: allolactose (异乳糖) an alternative form of lactose How can lactose be metabolized to allolactose? Repression is somewhat leaky: a low basal level of the lac operon products is always present No permease and -galactosidase