University:
Swansea University
Course:
PM134 | Microbiology
Academic year:

2023
Views:

201

Pages:

3
Author:

Amal J.

1When lactose is Present-A regulatory gene simply describes a gene that codes for Prinvolved in regulating the expression of other genes.At any one time only two Subunits of repressors appear to I#to the Operator and binding occurs in the major grous ofds-helical DNA There are normally 20-40 lac repressormolecules in the cells.H has two recognition sites: a DNA binding site andallostoric siteWhen the repressor binds to allolactose. proten undergoseconformational change : this Slight alteration in the shapichanges the the affirity for Operator .How the Presence of Inducer trigger the expression of LACoperonwhen inducer is present it binds to allosteric site of laerepressor, thereby inactivating its operator binding site howlautose. does not this effect rather allolactose doce.formation of allolactose is catalyzed by beta galactosicInactivation of lac repressor permits the induction of transeof the sinutural gene of lac openon and through treat of polycistronic m-RNA the enzyme. beta galautosidase, betagalantasicle permease and transacetylace are formed.Lactose Opennwhen lactose Present .-Need to make lactose digesting encymeeDNAlac1laczlaneylaca21RNA polyMRNA3'5,5'BpermearTransacttylaus.galastristonproteinAllolactoseInactive.(Inducer)representb)lactoc Present, Repressor Inactic,Operan onlautose is allostork regulator of repressor Protein.When lactose AbsentRepressor Protein is produced by the regulatory i gene , Therepressor protein binds to the operator region due to whichRNA polymerase cannot proceed with the trans cription of Structural genes and hence ,no enzymes are produced-A repressor protein is continuosly synthesised .It sits onsequence of DNA just in front of the lae openn the OperatSiteThe repressor proten blocks the Promoter site where the rpol settles before it starts transvribing.No lactoseWhen loutose is absent the lac repressor binds tightly tooperator. It gets in RNA polymerase's way / preverting transaPromoterXCAPSileOperator lacz lacy lacARNA polymeraeRepressurFour situations\Glucoe Present / lactoe absent - No transcription2.Glu present ,lac PreNo transcription3.Glu absent / lac absentNo transcription.4.Glu absent ,lac Presenttranscription account