Chapter 14 Flashcards
What is gene regulation
The level of gene expression can vary under different conditions
What are constitutive genes
Genes that are unregulated and have a constant level of expression
What is the benefit of gene regulation
It encodes proteins only when they are required
How is gene expression regulated during transcription
Genetic regulatory proteins bind to dna and control rate of transcription
Transcription stops soon after beginning due to formation of transcriptional terminator
What three things can stop translation from starting
Translational repressor proteins can bind to mRNA
Riboswitches can produce mRNA confirmation
Antisense RNA can bind to mRNA
When else can regulation occur of gene expression in bacteria
When a protein undergoes post translational changes to make it a functional protein
What does transcriptional regulation involve
Repressors which bind to DNA and inhibit transcription
Activators which bind to DNA and increase transcription
What is negative and positive control in regards to regulation
Negative is transcriptional regulation by repressor proteins and positive control is regulation by activator proteins
How do effector molecules affect transcription
They bind to regulatory proteins but not the dna directly
Also known as inducers because they can bind activators and repressors and either prevent them or cause them to bind to DNA
These genes are termed inducible
What do corepressors and inhibitors do for transcription
Corepressors bind to repressors and cause effector molecules to bind to DNA
Inhibitors bind to activators and prevent effector molecules from binding
These genes are termed repressible
When there is an inducer present what happens
It causes a conformational change that inhibits the ability of the repressor protein to bind to DNA and transcription proceeds
What happens when an inducer is bound to an activator protein
It enables the activator protein to bind to the DNA and activate transcription
What happens when a corepressor is bound to the repressor protein
Conformational change occurs that allows the repressor to bind to DNA and inhibit transcription
What happens when an inhibitor is present
Causes a conformational change that inhibits the ability of the activator protein to bind to the DNA which inhibits transcription
What is enzyme adaptation
Enzyme appears in the cell only after the cell has been exposed to the enzymes substrate
What is an operon
Region of DNA that involves sequences that aren’t structural or expressed parts of the DNA
Consists of a few structural genes under control of one promoter
What is a polycistronic mRNA
Contains coding sequence for two or more structural genes
This allows bacterium to regulate a group of genes that encode proteins with a common functional goal
What DNA sequences operons contain
Promoter, terminator, structural genes, operator
What does the lac operon and lacI gene do
Lac operon controls lactose metabolism
LacI gene is important for regulating the operon
Are are the elements of a lac operon
Promoter which binds RNA polymerase
Operator which binds the lac repressor protein
Cap sit which binds the cap
What are the structural genes of the lac operon
LacZ which encodes beta galactosidase
LacY which encodes the lactose permease
LacA which encodes galactoside transacetylase
What are some characteristics of the lacI gene
Not part of lacrosse operon
Has its own promoter
Expressed at low levels and encodes the lac repressor
What two things regulate the lac operon
Repressor protein
Activator protein
What happens in the absence of inducer allolactose
The repressor protein is tightly bound to operator site and inhibits the ability of the rna polymerase to transcribe the operon
What happens when allolactose is available
Binds to receptor and changes confirmation of repressor protein which prevents it from binding to operator site so RNA polymerase can transcribe the operon
What happens when lactose becomes available
A small amount is converted to allolactose by beta galactosidase and the allolactose binds to the repressor and causes it to fall off operator site
Then lac operon proteins are synthesized which promotes efficient uptake and metabolism of lactose until lactose is depleted and allolactose levels decrease
What is catabolite regression
When exposed to both lactose and glucose the E. coli uses the glucose first so catabolite regression prevents the use of lactose
What is diauxic growth
The sequential use of two sugars by a bacterium
What is cyclic amp
Produced from atp via adenylyl Cyclase
Binds to CAP
What is the camp-CAP complex an example of
Transcriptional regulation that is inducible and under positive control
How is the camp-CAP complex related to the lac operon
It binds to the CAP site near the lac promoter and increases transcription
When glucose is present adenylyl Cyclase is inhibited which decreases levels of camp so it can’t bind to CAP and transcription rate decreases
What are the three operator sites in the lac operon
O1 which is next to the promoter
O2 which is downstream in the lacZ coding region
O3 which is slightly upstream of the promoter
What must the lac repressor do to cause repression
Must bind to two of the three operators
Can be O1 and O2 or O1 and O3 but not O2 and 3
What is the significance of the lac repressor binding to the two operator sites
The dna forms a loop which brings the operator sites closer together
What does trpL and trpR do
TrpR encodes the trp repressor proteins and functions in repressing
TrpL encodes a short leader peptide and functions in attenuation
What happens when tryptophan levels are low
Tryptophan doesn’t bind to trp repressor protein which prevents repressor protein from binding to operator site
What happens when tryptophan levels are too high
Tryptophan acts as a corepressor that binds to trp repressor protein and tryptophan-trp repressor complex then binds to the operator site to inhibit transcription
What happens when attenuation occurs
RNA is transcribed only to attenuator sequence and then transcription is terminated
When does attenuation occur
In bacteria because transcription and translation are coupled
Transcription will terminate before the entire mRNA is made which is facilitated by an attenuator
Why are two tryptophan codons found in the mRNA from the trpL gene important
It’s a way for bacterium to sense tryptophan levels
mRNA from trpL can form stem loops
