Ch. 8 Part 2 Flashcards
What is gene expression?
transcription of gene into mRNA
followed by translation of mRNA into protein
What inhibits gene expression and decreases enzyme synthesis?
Repression is mediated by repressors. What is the function of repressors?
T/F Default position of a repressible gene is ON
Repression
block transcription
TRUE
T or F Constitutive proteins are needed at the same level all the time
True
Induction turns on ______ ______
Induction is initiated by substances that induce enzyme synthesis called what?
What is the default position of an inducible gene?
gene expression
Inducer
OFF
what do Microbial genomes encode and how are they expressed?
- proteins that are not needed all the time
- expressed only as needed.
_____________ genes need to be induced to be regulated while ___________ genes need to be repressed for regulation?
inducible genes
repressible genes
- what is the promoter in the operon model of gene expression?
- segment of DNA that controls transcription? (located downstream of promoter)
- what do operons include?
- segment of DNA where RNA polymerase initiates transcription
- operator
- set of operator and promoter sites, and
structural genes they control
What is a collective term for inducers and repressors?
How do effectors affect transcription indirectly?
Effectors
by binding to specific DNA-binding
proteins
what is the repressor’s role and what is it called?
inhibitory, so it is called negative control
What do repressor molecules bind to?
This protein becomes active and binds to what?
allosteric repressor protein
the Operator (region of dna near promoter)
In an inducible operon structural genes are only transcribed if what?
an inducer is present
In the absence of __________, the repressor (product of the gene) binds to the operator, preventing transcription
lactose
In the inducible operon, the repressor is __________ while the operator is __________.
repressor is active
operon off
In the lac operon of E. coli what is needed to metabolize lactose?
Where are the structural genes for these enzymes (Z, Y, and A)?
- is their transcription regulated separately or together?
Three enzymes encoded by the lac operon
adjacent on the chromosome
- TOGETHER
The control region includes what 2 things? What happens at each?
- Promoter: where transcription begins
- Operator: stop or go signal
In repressible operons, structural genes are transcribed until when?
they are turned off
- E.g. trp is the operon of which bacteria in the repressible operon?
- What is the corepressor that binds and activates the repressor to bind to the operator?
- E. coli
- Excess tryptophan
INDUCIBLE OPERON MODEL OF GENE EXPRESSION
In the presence of lactose, what binds to the repressor?
What does this cause?
A metabolite of lactose:
allolactose (inducer)
the repressor can’t bind to the operator and transcription
occurs
T/F operons are negative regulation
TRUE
POSITIVE REGULATION
Catabolite repression inhibits cells from what?
using carbon sources other than glucose
What is the result of the excess tryptophan corepressor?
stops the synthesis of tryptophan
POSITIVE REGULATION
When does Cyclic AMP (cAMP) build up in a cell?
When glucose isn’t available
Define alarmone and give an example of one?
a chemical that promotes a cell’s response to environmental or
nutritional stress
- cAMP
POSITIVE REGULATION
cAMP binds to the ________ _________ ________(CAP) that in
turn binds the lac promoter,
initiating _____________ and
allowing the cell to use _________.
Catabolic activator protein
transcription
lactose
