Gene Expression in Prokaryotes Flashcards
True or False - constitutive genes are continuously expressed in most cells
True
Genes whose transcription status is normally on are _____ and genes whose status is normally off are _____
On = repressed Off = induced
Difference between positive and negative regulation + both their end results
Positive = presence of activator which allows for transcription
Negative = presence of repressor = does not allow for transcription
What is the purpose of allosteric effectors
they are indicated of changes in the environment for changes the cell need to adapt to (transcriptional profile)
Allosteric effectors bind to regulatory proteins to modulate their ______
affinity for DNA
Is allolactose an effector for a repressor or activator?
it is an effector for repression - it changes the shape of lac repressor so it unbinds from DNA and allows for transcription
Is cAMP/CAP an example of an effector for activation or repression?
It would be for activation - when the effector (cAMP) binds to CAP it can bring efficiently onto the DNA and allow for transcription
An inducer can act on an activator or repressor protein to ____ gene expression
up-regulate
A corepressor can act on an activator or repressor protein to ___ gene expression
Down regulate
What are the 2 ways an inducer can induce translation?
- displacing a repressor
2. enabling an activator
What are the 2 ways a repressor can disable translation?
- enabling a repressor
2. displacing an activator
An inducible operon is constitutively ___ until ____
Off until induced
an inducible + repressible operon is regulated by a _______system
repressor
Steps in an inducible operon (NOOOOOOO picture)
- RNA pol is blocked because the repressor is on the DNA strand
- When the inducer is added, it forms the repressor/inducer complex
- RNA pol can transcribe now
- Ribosomes translating mRNA
- Forms polypeptides
A repressible operon is constitutively ___ until _____
On until repressed
Steps in a repressible operon
- RNA polymerase is translating mRNA
- Repressor is inactive and can’t bind to the operator until co-repressor is added
- Polypeptides are formed
Co - repressor added - translation is blocked due to repressor/co-repressor complex
The Lac operon is a ____ because it is usually turned off but can be turned on in the presence of ____ - _____
the lac operon is an inducible operon
turned on in the presence of an inducer - allolactose
The lac operon is only expressed when ____ is present and _____ is absent
the lac operon is only expressed when lactose is present and glucose is absent
Two regulatory proteins turn the operon “on” and “off” in response to lactose and glucose levels: _____ + _____
The lac repressor and the catabolite activator protein
