CHAPTER 14 Flashcards
(26 cards)
Gene Regulation
Ability to control the level of expression varies under different conditions
The benefit of regulating genes
Only produced when required
Constitutive
Genes that are unregulated
-Constant levels of expression
-Encode proteins necessary for survival
What is the benefit of gene regulation?
It allows proteins to be produced only when required, optimizing resource use in the cell.
How can gene regulation occur?
Regulation can occur at any stage in gene expression: transcription, translation, or posttranslational processing.
Most common way of regulating genes in bacteria
Initiating transcription
-RNA synthesis can increase or decrease
Two main types of regulatory proteins involved in transcriptional regulation
1- Repressors
2- Activators
Repressors Proteins
-Bind to DNA
-Inhibit transcription
-Negative control
Activators Proteins
-Bind to DNA
-Increase transcription
-Positive control
Small Effector Molecules
-Affect transcription regulation
-Bind to regulatory proteins, NOT DNA directly
Inducers
-Increase transcription
-Bind to activators and makes them bind to DNA
-Bind to reducers and prevents them from binding to DNA
-Called inducible genes
What are repressible genes?
Genes that can be inhibited by corepressors, which bind to repressors to enable them to bind to DNA.
What is the lac operon?
A regulatory unit in E. coli that consists of several structural genes and is controlled by one promoter, involved in lactose metabolism.
Corepressors
-Inhibit transcription
-Inhibitors bind to activators and prevent the DNA binding
-Called irrepressible genes
Absence of Inducer
The repressor protein blocks transcription
Presence of Inducer
-Conformational change
-Repressor protein binds to DNA
-Transcription proceeds
When can an activator protein bind to DNA
-Only binds to DNA if an inducer is present (bound to activator protein)
-Activates transcription
What is the function of lacZ, lacY, and lacA in the lac operon?
-lacZ encodes β-galactosidase
-lacY encodes lactose permease
-lacA encodes galactoside transacetylase
How does the lac repressor regulate the lac operon?
Without allolactose, the repressor binds to the operator site, inhibiting transcription. Allolactose induces the repressor to detach, allowing transcription to proceed.
Catabolite Repression
A regulatory mechanism where E. coli prioritizes glucose over lactose when both are present, inhibiting the expression of the lac operon until glucose is depleted.
How does cyclic AMP (cAMP) function in the regulation of the lac operon?
cAMP binds to the Catabolite Activator Protein (CAP), enhancing transcription when glucose is low.
What is the trp operon?
A set of genes in E. coli involved in the biosynthesis of tryptophan, regulated by the trp repressor and leader peptide.
How does tryptophan act in the regulation of the trp operon?
When tryptophan levels are high, it binds to the trp repressor, allowing it to bind to the operator and inhibit transcription.
What is attenuation in the context of the trp operon?
A regulatory mechanism where transcription is prematurely terminated based on the availability of tryptophan, involving the formation of stem loops in mRNA.
