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Bio Exam II

Gene Regulation

lac operon model- the basics - e. coli: normal stomach bacteria, adjusts based on host - humans drink milk= e. coli digests lactose
Induction Turning on gene expression
inducer compound that stimulates gene expression
inducible enzyme -coded for by inducer gene - produced in response to inducer - contrast w/ constitutive enzymes
Operon - complex in DNA: group of genes with related functions - regulatory DNA sequences - promoter: RNA poly. binding site not transcribed - operator: "switch" sequence for gene expression - 3 genes: lac z, lac y, lac a
Negative regulation of lac operon - no lactose= operon off, no expressed - with lactose= operon expressed
Involves Repressor repressor gene: codes for repressor protein, regulates gene expression - always on constitutive expression - not always part of operon
Lac Repressor Activity - no lactose: repressor binds to operator - RNA poly. can bind promoter, can't transcribe genes
Lactose affects lac expression - lactose enters cell, converted to allolactose - binds 2nd site on repressor protein - inactive by changing structure= cannot bind operator - allolactose is a non-competitive inhibitor of repressor protein
Allolactose in the inducer - induces lac operon genes by inactivating the repressor protein - allows transcription to occur - results in low levels of lac expression
What is transcribed? - 1 long mRNA w/ all 3 genes - each gene w/ own start & stop codon
NO NUCLEUS transcription and translation happens simultaneously
Positive Control of Lac Operon - positive control: regulation by an activator that binds DNA to stimulate transcription (high expression when active) - lactose can be used for E - glucose present= use first - lac operon expression responds to lactose & glucose levels
Lac Promoter Inefficient - low affinity for RNA pol. - Solution: CAP- catabolic activator protein - increases affinity of promoter for RNA pol - CAP inactive alone - CAP active when bound to cAMPT: cyclic AMP (adenosine monophosphate)
Effects of CAP-cAMP - low glucose= cAMP increases - CAP-cAMP binds; CAP binding site next to RNA pol. binding site - increases RNA pol. binding - bonds double helix - = positive control ( increases expression)
Lac Operon Activity:4 Structures - high glucose/ no lactose= no CAP, repressed, no expression - no glucose/ high glucose= CAP, induced, high expression - no glucose/ no lactose= CAP, released, no expression - high glucose/ high lactose= no CAP, induced, low expression
Eukaryotic gene regulation - eukaryotic cells respond to envi. - multicellular: allows for specialization & organization - achieved through differential gene expression
Regulation of Transcription Initiation - more complex than prokaryotes - involves DNA sequences & transcription factors ( proteins that bind DNA) (promote or inhibit transcription initiation)
Post- transcriptional regulation - length of poly-a-tail affects level of expression
Alternative Splicing - different polypeptides from same gene
Post-Transcriptional Regulation - polypeptides often processed= final protein - must be folded correctly - often chemical modifications
Created by: tennadeleta.