Chapter 18: Gene Regulation

stages of gene regulation in E coli

why is transcription control most important step in gene regulation

if everything its transcribed perfectly here, following steps don't have to be as regulated

activator

DNA binding protein to turn on or activate gene transcription/expression

positive regulation of gene expression

requires activator to turn on expression of structural genes

RNA polymerase requires active activator/inducer complex at regulator protein binding site, inducer must be added to activate activator

repressor

protein that binds to DNA to turn off gene expression

negative regulation of gene expression

repressor required to shut off expression of structural genes

repressor protein binds to DNA to block transcription and shut off expression

addition of inducer presents repressor/inducer complex from binding, allows transcription to continue

operon

DNA segment whose translation products are involved in same metabolic pathway

benefits of operon oganization

close proximity of genes causes transcription and translation to occur together, using less time and energy to find each other in cell and perform required functions

genetic components of lac operon

promoter (P), operator (O) and structural genes (SG)

lac operon

regulation and coordinated expression of genes required for lactose utilization in E. coli

Monod an Jacob

id repressor gene (I), promoter gene (P), regulatory element operator (O), and 3 structural genes (lacZ, lacY, lacA)

lacY

lactose permeate

transport of lactose from environment

lacZ

beta galactosidase

cleaves lactose into glucose and galactose

at low levels converts lactose into allolactose (inducer)

lacA

beta galactoside transacetylase

what happens in lac operon in presence of lactose, absence of glucose

cAMP increase and bind to CAP

cAMP-CAP complex binds to lac promoter

activates high levels of transcription of lac genes

lacZ converts lactose to allolactose

allolactose binds to and inactivates lac repressor

results in transcription of lac operon

what happens in lac operon in presence of lactose and glucose

glucose preferred

cAMP levels decrease, cAMP-CAP complex doesn't form or bind to lac promoter

lac genes not transcribed

cAMP

cyclic AMP adenosine monophosphate

single molecule, regulates lac operon via its levels in cells

high glucose levels, decrease cAMP, vice versa

regulates lac operon by binding to CAP

CAP

catabolite activator protein

binds to lac promoter to relate lac operon activity

inducer

effector molecule that turns on gene expression when bound to activator/repressor

how does inducer alter negative controlled gene expression with a repressor

when inducer is absent, repressor binds to regulator protein binding site and blocks transcription

when inducer is present, it binds to repressor and inactivates it, transcription proceeds

what is polycistronic mRNA

mRNA with more than 1 shine delgarno sequence

how are different polypeptides translated from polycistronic mRNA in prokaryotic cells

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