control of gene expression from bacteria

constitutive cells

continuous processes/pathways (not regulated by external signals)

inducible genes

mechanisms that allow synthesis of genes only when needed

repressible genes

mechanisms that shut down genes when they are no longer needed

what do DNA binding proteins contain

domains of 60-90 amino acids that recognize DNA sequences and grooves in DNA

what is a motif

mediate a function (binding, regulatory processes)

what type of binding do motifs undergo to promoter

non covalent

helix turn helix motif

DNA binding structural motif

zinc fingers motif

structural domain for controlling gene expression

leucine zipper motif

dimerization and DNA binding

how is transcription in bacteria regulated

operon

regulation of transcription is regulated by

regulator protein/transcription factor

what part of promoter does the regulator bind to

operator

what is an operon

group of structural genes and sequences that control transcription

what does the operator overlap with

3’ end of promoter and 5’ end of transcription site

negative regulator proteins

repressors, inhibit transcription

positive regulator proteins

activator, stimulates transcription

inducible operons

transcription of operon is off, transcription turns it on

repressible operons

on, something happens that turns it off

how does regulator gene keep transcription off

encodes for an active repressor protein that blocks binding of RNA polymerase to promoter

inducible

something inactivates repressor which induces transcription

inducer role in transcription

binds to inhibitor/repressor and inactivates it by causing conformational changes, repressor cant bind to DNA, RNA polymerase can activate transcription

without inducer

binds to operator, blocking transcription

with inducer

binds to repressor, releases from operator, transcription proceeds

what is an example of a negative inducible operon

lac operon in e coli (lactose is an inducer)

what does the regulator protein need to bind to the promoter/operator

co factor/ corepressor

repressor is __ in the absence of co factor

inactive

example of negative repressible operon

trp operon in e coli

how does trp operon in e coli work to ensure tryptophan is only synthesized when levels are low

repressor protein: in inactive form, repressor cant bind to operator allowing transcription

co-repressor (trp): when trp levels are high, trp acts as a co-repressor by binding to repressor protein

transcription inhibition: binding of trp to repressor causes conformational change, enables repressor to bind to operator and block transcription

regulatory protein

activator

what does activator do

bind to operator and induce transcription

what is catabolite activator protein (CAP)

positive activator, binds upstream of promoter and enhances binding of RNA polymerase to promoter

in the lac operon what is lacI

regulatory gene, active repressor

in the lac operon what are the structural genes

lacZ, lacY, lacA

in the lac operon what is lacZ

beta-galactosidase, catalyzes e coli to breakdown lactose to glucose and galactose, and can convert lactose into allolactose

in the lac operon what is lacY

permease, catalyzes the transport of lactose across the bacterial cell membrane

in the lac operon what is lacA

thiogalactoside transacetylase, function unclear

what happens in the lac operon in the absence of lactose

very little operon transcribed, repressor protein (lacI) binds to operator (lacO) and inhibits transcription

what happens if lactose is added to the medium instead of glucose

rate of synthesis of lac operon increases 1000x in 2-3 mins

what is coordinate induction

simultaneous synthesis of several proteins by a specific molecule, the inducer

lac operon, what keeps operon in the on position

beta galactosidase

what is the negative inducible operon in the lac operon

allolactose, binds to repressor and repressor releases from operator

lac operon, what induces expression of three structural genes (lacY, lacZ, lacA)

RNA polymerase binds to promoter

lac operon, what happens when there is no more lactose

no more allolactose made, repressor binds to operator and inhibits transcription

does repression fully shut down transcription

no

low levels of what are always present in cells

permease and beta-galactosidase