Gene Regulation Flashcards
Through which two mechanisms is expression of the tryptophan gene regulated?
Through Feedback repression and transcriptional attenuation.
The general ground state of eukaryotic genes is ____, while the general state of prokaryotic genes is ____.
off
on
How many different RNA polymerases are there in eukaryotes and what is the function of each?
RNA polymerase II transcribes all DNA
RNA polymerase I transcribes rRNAs
RNA polymerase III transcribes tRNAs
What are cis-acting agents?
Regions upstream/downstream of genes that allow RNA polymerase to bind with high activity and therefore, express genes with high activity.
Whats are the different cis-acting agents and what is the function of each of them?
Promotor sequences: transcription begins here as this is the location of RNA polymerase binding.
Promoter proximal elements: 200b from the promoter, binding site of various transcription factors, which are necessary for maximal translation. Present in all cells.
Upstream activation sequences: over 100Kb away from promoter region, enhance transcription. As they are cell specific, play a role in cell differentiation. Helps recruit transcriptional proteins.
Does acetylation of histone tails lead to higher or lower transcription levels?
Higher, as histones are less able to interact with nucleosomes and so genes are more accessible to RNA polymerases.
What is the function of SWI-SNF?
Move around nucleosomes, making genes more or less accessible to RNA polymerases.
Why are not all genes expressed at once in prokaryotes? In eukaryotes?
Prokaryotes are metabolically diverse and expression of many genes at once is metabolically demanding. It is more efficient to express genes that are necessary in the current environment. Additionally, prokaryotes are able to down-regulate and up-regulate genes rapidly.
Eukaryotes do not express all genes at once as this allows differentiation of cells (through upstream regulator sequences) and is metabolically efficient to express genes necessary at the particular time.
What is the difference between negative and positive gene regulation?
Negative regulation: a repressor (represses transcription) binds to the promoter region, not allowing the RNA polymerase to bind.
Positive regulation: promoter must bind to the DNA for RNA polymerase to bind.
Where on the DNA does a repressor bind?
Operator region, between the promoter and the gene.
What is the difference between an activator, a repressor and an inducer?
A repressor prevents binding of RNA polymerase and so prevents transcription.
An activator helps RNA polymerase to bind and begin transcription.
An inducer binds to the repressor and to the activator allosterically to stop the repressor from binding to DNA or to help the activate bind to DNA, inducing transcription.
In negative regulation of the lac operon, what functions as the repressor and what functions as the inducer?
Repressor: lactose repressor, product of lacI
Inducer: low m.w. beta-galactoside (allo-lactose)
In positive regulation of the lac operon, what is the inducer?
cAMP
What are the steps in positive regulation of the lac operon?
When glucose levels are low, there is no inactivation of adenylate cyclase and cAMP can be made from ATP. cAMP acts as an inducer, binding to CAP allosterically so CAP can bind to the promoter. This bends DNA, applying torsional pressure to unwind DNA and transcribe.
What is the difference between feedback inhibition and feedback repression?
Feedback inhibition: Product of a pathway binds allosterically to the first enzyme to reduce production of the product.
Feedback repression: product interacts with a regulatory protein to stop transcription of genes encoding enzymes in the pathway.
