Exam 3 - Lecture 15 Flashcards
what are the two approaches to protein regulation?
- regulation of gene expression (transcription/translation)
- alter activity of enzymes and proteins (posttranslational)
how is transcription regulated? what kind of genes allow for this regulation?
genes aren’t expressed all the time
- constitutive/housekeeping genes
- inducible genes
- repressible genes
what are inducible genes and what pathways do their enzymes function in?
- genes that are usually off but can be turned on
- function in catabolic pathways
what are repressible genes and what pathways do their enzymes function in?
- genes that are usually on but can be turned off
- function in anabolic pathways
what reaction does beta-galactosidase catalyze?
hydrolysis of lactose into galactose and glucose
is the beta-galactosidase gene inducible or repressible? is it on or off in the presence of lactose?
- inducible gene
- only turned on in the presence of lactose
inducible enzymes are only present when their _________ is available
substrate
repressible genes are present unless the _____ _________ of the biosynthetic pathway is available
- end product
- (no need to make more of the product if it’s available)
induction and repression occur due to activity of regulatory proteins containing _____ _________ __________
DNA binding domains
what is negative transcriptional control?
binding of a regulatory protein (repressor) at the DNA regulatory site (operator) inhibiting initiation of transcription
true or false: repressor proteins can exist in both active and inactive forms
true
what two molecules can alter the activity of repressors?
inducers and corepressors
a repressor is bound to the operator. an inducer binds the repressor, causing it to detach from the operator.
does transcription occur? what kind of regulation is this?
- yes, transcription occurs
- negative control of an inducible gene
a repressor is not bound to the operator. a corepressor binds the repressor, causing it to attach to the operator.
does transcription occur? what kind of regulation is this?
- no, transcription stops
- negative control of a repressible gene
what is positive transcriptional control?
when an activator promotes transcription
an activator is not bound to the operator. an inducer binds the activator, causing it to attach to the operator.
does transcription occur? what kind of regulation is this?
- yes, transcription occurs
- positive control of an inducible gene
an activator is bound to the operator. an inhibitor binds the activator, causing it to detach from the operator.
does transcription occur? what kind of regulation is this?
- no, transcription does not occur
- positive control of a repressible gene
what represses lactose metabolism in the Lac operon?
- LacI repressor
what are the three structural genes coding for lactose uptake and metabolism?
lacZ, lacY, and lacA
what are the three operator binding sites for LacI tetramers? how does LacI bind?
- O1, O2, and O3
- binds TWO of the three sites; (always binds O1) O1 and O2 or O1 and O3
how does LacI block RNA polymerase from binding?
- it bends the DNA which blocks RNA pol from binding the operator
what binds the LacI repressor causing it to no longer bind to the operator?
allolactose
in the absence of lactose, does LacI bind to the operator?
yes
in the presence of lactose, does LacI bind to the operator?
no
what is the protein that positively regulates the lac operon?
catabolite activator protein (CAP)
CAP regulates the lac operon in response to the presence or absence of _________
glucose
do cells prefer lactose or glucose?
glucose
when glucose if present, will the lac operon be activated?
no; the cells prefer glucose and don’t need to use lactose
what are the two conditions required for activation of lac operon?
- absence of (or low) glucose
- presence of (or high) lactose
the Tryptophan (trp) operon only functions in the _________ of tryptophan
absence
what kind of control does the trp repressor do for the trp operon?
negative control
how many structural proteins does the trp operon code for?
5
what is attenuation (in the trp operon)? what structures allow for this to occur?
- the termination of transcription within the leader region, ending transcription before the gene is transcribed
- occurs through stem-loop structures in the mRNA depending on the levels of trp present
the trp leader sequence contains a short peptide called:
TrpL
if the amount of charged Trp tRNA is low, does transcription stop or continue? where does the antiterminator loop form on the trp mRNA?
- it continues
- antiterminator: regions 2 & 3
what two regions on the trp mRNA form the transcription terminator?
regions 3 & 4
riboswitches are a specialized form of transcription ____________
attenuation
what does folding of the mRNA leader sequence (riboswitch) determine?
whether transcription will continue or terminate
binding of what alters the folding response of the riboswitch?
an effector molecule to the mRNA
what is a regulon?
a set of genes or operons controlled by a common regulatory protein
what is an example of a global regulator in the lac operon?
CAP
many genes and operons are turned on or off in response to:
environmental conditions
what are four regulation mechanisms global regulatory systems often use? which is the most common*?
- two component signal transduction systems*
- phosphorelay systems
- regulatory systems
- alternative sigma factors
how many domains of life are two component regulatory systems found in?
all three
what are the two proteins found in the two component regulatory system?
- sensor kinase (histidine kinase)
- response-regulator protein
what are the characteristics of sensor kinase (histidine kinase)?
- extracellular receptor for sensing
- intracellular communication domain
what are the characteristics of the response-regulator protein?
- intracellular protein
- activated by sensor kinase
- DNA binding protein (activator/repressor)
activation of ________ ________ results in the phosphorylation of its histidine
sensor kinase
the ___________-__________ ________ is activated by sensor kinase
response-regulator protein
when the response-regulator protein is activated, a phosphate group is transferred from _____ to _____
His to Asp
EnvZ is a _________ ________ that phosphorylates in ______ osmolarity
sensor kinase; high osmolarity
OmpR is a ___________ __________ that regulates transcription when phosphorylated
response regulator
expression of what two outer membrane proteins do OmpR and EnvZ regulate? what is their regulation dependent on?
- OmpC and OmpF
- depends of osmolarity
match the following:
- OmpF
- OmpC
a. dominant when E. coli is in high osmolarity
b. dominant when E. coli is in dilute environment
1b. OmpF: dominant when E. coli is in dilute environment
2a. OmpC: dominant when E. coli is in high osmolarity
which is usually the protein that is on: OmpF or OmpC?
OmpF
match the following:
- OmpR represses
- OmpR activates
a. ompF
b. ompC
1a: OmpR represses ompF
2b: OmpR activates ompC
