Regulation pt. 1 Flashcards
Why is regulation important
Saves energy and space (can’t make all proteins all the time - energetically costly/space), helps adapt to changing conditions, activities of some gene products are detrimental (spore formation)
What is the exception to turning genes on and off
housekeeping genes are always expressed - constitutive enzymes (enzymes that metabolize glucose)
what is an operon
genes under the same promoter - when it gets turned on, all the genes on operon turn on
what do polycistronic mRNAs have multiple of
ribosome binding sites
how do regulatory proteins regulate / what can they be
they regulate the target gene by binding the regulatory sequence on the opperator/ can be activators or repressors - can have positive or negative affect
why is the inverted repeat symmetry important for regulatory sequences / what happens as the match of the symmetry grows
the regulatory proteins almost always bind as dimers / the closer to a perfect match the higher the affinity
what is a ligand
specific low-molecular-weight compound that alters the DNA-binding of the regulator
what is allosteric regulation
the ligand changing the shape of the regulatory protein which in turn changes the proteins affinity for DNA
what do repressors do / where do they bind / what are the two types of ligands are there
they always block transcription / to the DNA sequence in front of a protein but after the promoter sequence / an inducer or a corepressor
how does a corepressor ligand regulate / how does levels of ligand in cell change the repression of a gene
it binds to the repressor which then binds to the DNA and turns off operon / lower levels of the ligand in the cell means that the regulator protein will lose its corepressor and no longer bind to the DNA - leads to expression of the gene
how does an inducer ligand regulate
the regulator protein is already bound to DNA - in presence of ligand it loses affinity for DNA and the transcription of the gene is induced
what are activators / what do they almost all require
stimulate transcription / almost all require a ligand
what is the activator ligand called / where does the activator+ligand complex bind
an inducer / before the promoter of the operon (bends the DNA to contact the RNA polymerase)
what does LacZ (beta-glactidase) do
degrades lactose into constituents (saccharides which go into glycolysis & feed bacteria)
what is diauxic growth / what kind of growth curve does the regulation of lactose exhibit
two phased growth / diauxic growth (very little lag phase, growth with glucose, lag, growth with lactose, stationary)
what does LacY do
imports lactose & protons at the same time (symporter)
what does induction mean for lacZ in lactose utilization
it turns the production of beta-galactosidase on only when lactose is present
what is the key regulatory component 1 in lactose utilization
LacI - constitutavely expressed
what does LacI bind to repress expression of lactose operon / why is it important that the lac operon is never fully off
lacO and lacOi / always up to 10 molecules of lacZ per cell because it allows for the production of allolactase
what is allolactase / why is it important for presence of lactose
allolactase is the inducer ligand for lacI / allolactose is made from lactose by lacZ when there are low levels - keeps the operon sensitive to the levels of lactose
what does the cyclic AMP receptor protein (cAMP CRP) do
binds to cAMP and activates lactose operon when bacteria are starving
what is catabolite repression
the presence of a more favorable catabolite (glucose) prevents the expression of operons that enable catabolism of a second carbohydrate (lactose)
what does inducer exclusion do
keeps lactose out of the cell in the presence of glucose due to the phosphorylation of the IIA protein involved with PEP
what happens when glucose is not present in the cell
the phosphorylation status of the IIA changes and is now phosphorylated so it cannot inhibit lacY - also produces cAMP from ATP
what is feedback inhibition
if end product of pathway is present the pathway will not be turned on
what three types of regulation are used for the trp operon
feedback inhibition, transcriptional repression, transcriptional attenutation
how does trp itself regulate expression
it binds to the aporepressor that makes the holorepressor (feedback inhibition)
what is trpR / how does it prevent the transcription of the operon
the repressor of trp / binds to the corepressor which binds to the operator and prevents transcription
what does transcriptional attenuation do for the trp operon
fine tunes the expression of the operon - used in conjunction with repression / functions to halt transcription before structural genes
what does the attenuator site do / where is it located
forms two different loop structures that either terminate transcription (3:4) or promote (2:3) / between the transcriptional start site and the first structural gene
what does region 1 (leader) do in the attenuator
does nothing except for contain two Trp next to each other - the ribosome stalls here due to the low trp levels as there is no charge on the Trp (allows for the 2:3 loop to form)
would you expect transcriptional attenuation (down-regulation of the operon) to work in a eukaryotic cell
no as it requires the robosome to be present on the transcript
