lecture 21, 22, 23 Flashcards
what is the purpose of regulating gene expression?
create different proteins for different activities or to conserve energy
what is needed to regulate gene expression?
recognize environmental conditions and respond to such by turning genes off/on
what does RNA pol need to transcribe?
it needs to be able to bind to a promoter and move from the promoter downstream without dissociating from DNA
what is the process of binding to a promoter called?
recruiting
how do activators work?
they allow for transcription by binding to activator binding sites on the DNA
how do repressors work?
they block transcription by binding to operators on the DNA
what are activators?
proteins that promote transcription by recruiting RNA pol and keeping it on the promoter
what are repressors?
proteins that block transcription by blocking RNA pol recruitment and movement
allosteric effectors
small molecules that bind to a protein in a specific site and regulates activity
what is an effector that regulates activity in a positive way called?
an inducer
what happens to a protein when an effector binds to its allosteric site?
it causes a confirmation/structural change in the protein
what does the result of an effector binding to a protein result in?
it can allow or prevent proteins from binding DNA
what happens if an activator doesn’t bind with an effector?
the activator is unable to bind with the activator binding site and is unable to promote transcription
what happens if a repressor does not bind with an effector?
the repressor stays bound to the operator and continues to block transcription
operon
a group of genes that are regulated together from the same promoer and transcribed into a singular mRNA
what does it mean when genes in an operon are coordinately controlled?
one mRNA can translate into more than one protein
what is the difference between an operon vs a single gene?
only one gene can be formed by the ribosome in a single gene, whereas in an operon the ribosome can create multiple proteins
what controls the lac operon?
the repressor protein
what is beta-galactosidase?
a protein that breaks down lactose
what is permease?
a protein that transports lactose into the cell
what is transacetylase?
a protein that modifies galactosides and detoxifies byproducts of lactose metabolism
what proteins are required for lactose metabolism?
beta-gal and permease
why is the repressor typically active in the lac operon?
to save energy if there is no lactose to be metabolized
what does lactose get broken down into?
galactose and glucose
apart from galactose and glucose, what else can beta-gal break lactose into?
allolactose
what is the inducer in the lac operon system?
allolactose
what happens when allolactose present in the system?
it binds to the repressor and is released from the operator, allowing for transcription
when trying to study the lac operon, what issues can arise from a standard system?
lactose is broken down by beta-gal which drops the concentration during an experiment
what was the solution Jacob and Monod came up with to work around the lactose concentration drop?
utilize IPTG as the allosteric inducer
why was IPTG effective as an alternative to lactose?
it had similar properties to lactose and was not broken down by beta-gal
what did Jacob and Monod do to be able to create a partial diploid in a haploid system?
utilized F’ factors to introduce an additional copy of the gene
inducible promoter
operon is expressed only in the presence of an inducer
constitutive mutant
operon is expressed in the absence of an inducer
cis acting element
activity occurs on the same DNA molecule as the element
trans acting element
activity occurs on other DNA molecules of the element
are operators cis or trans acting?
cis-acting
are repressors cis or trans acting?
trans acting
what occurred to lac operons that had mutated operators?
the operon would always be active because the repressor couldn’t bind to the altered site
what occurred to lac operons that had mutated lacl?
it would create super repressors that could not bind to the inducers or not create a repressor at all
what is the preferred energy source for our cells?
glucose
why is it better to have glucose over lactose?
it saves energy because its one less step in metabolism
when glucose levels are high, what is the result?
ATP is high which reduces cAMP production
when glucose is low, what is the result?
ATP is low which kickstarts cAMP production
when there is less cAMP in the system, what effect does that have on the lac operon?
it is not able to be activated because the cAMP-cap complex is not formed
when there is a lot of cAMP in the system, what effect does that have on the lac operon?
it causes the cAMP-cap complex to form which activates the lac operon
describe the cAMP-cap complex
cAMP acts as an allosteric inducer to cap, whose binding site sits next to the promoter and activates the lac operon
what happens to DNA when CAP binds to it?
DNA bends to enhance the interaction between RNA pol and the promoter
what regulates the lac operon?
CAP
what variables result in no lac mRNA being produced?
high amounts of glucose, no cAMP, and no lactose
what variables result in a lot of lac mRNA being produced?
low amounts of glucose, high cAMP, and lactose
in what case would lac mRNA be produced when theres glucose present?
lactose being present
What function does AraC serve in the ara operon?
It can be an activator and a repressor
what is the allosteric inducer of AraC?
Arabinose
what happens when arabinose is not present in the ara operon?
AraC represses the operon by bending it
what happens when arabinose is present in the ara operon?
transcription can occur
in the trp operon, what represses it?
tryptophan
what does it mean for mRNA production to attenuate?
to decrease production
what happens when there’s a high level of Trp?
the ribosome completely translates the leader region, region 3 pairs with 4 and terminates transcription
what happens when there’s a low level of Trp?
ribosome stays at leader region to encode for more Trp, region 2 pairs with 3 and transcription occurs
lytic cycle
when a phage multiplies in a host cell and kills it
lysogenic cycle
When a phage’s DNA integrates with a host’s chromosome
what cycle will a phage go into if resources are abundant?
lytic cycle
what cycle will a phage go into if resources are not available?
lysogenic cycle
does a phage that undergoes lysogenic cycle stay like that forever?
no, it will eventually transition to the lytic cycle when resources become plentiful
How is plaque created?
when phages kill their bacterial host
cloudy plaque
some bacteria is alive and are of a wild-type temperate phage
clear plaque
all bacteria has been lysed and is of a mutant phage that is lytic
what promoters control what cycle a phage goes into?
Pr and Prm
which gene will encode the lytic cycle?
cro
which gene will encode the lysogenic cycle?
cl
which promoters does the Cl repressor bind to from strongest to weakest affinity?
O1 > O2 > O3
which promoters does the Cro repressor bind to from strongest to weakest affinity?
O3 > O2 > O1
which gene encodes for virulence?
cro
