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What is the promoter?
It is a region of a gene in the DNA of prokaryotes at which the transcription of a gene is initiated.
What is an operator?
It is the DNA region where the transcription factors bind to regulate gene expression
How can you inhibit production of tryptophan in a cell immediately?
By feedback inhibition which acts upon the first enzyme in the anabolic pathway.
What happens with E. Coli's tryptophan regulon when tryptophan is available in cell's environment?
The available tryptophan binds to the repressor of the TRP operon, the represor becomes active and binds to the TRP operator and blocks the binding of the RNA polymerase.
What type of operon is the TRP operon?
A repressible operon
Why is the TRP operon repressible?
Because the transcription of the TRP operon is inhibited (repressed) when tryptophan is in excess, so the cell doesn't waste energy producing an aminoacid which is available.
What is a correpressor? Give an example.
A small molecule that cooperated with a repressor molecule to switch an operon off. For example tryptophan is a correpressor.
What is negative gene regulation?
A way to control gene expression by switching transcription off. Usually, the active repressors block transcription.
What is positive gene regulation?
A way to control gene expression by which a regulatory protein interacts directly with the genome to switch transcription on.
Why is the LAC operon inducible?
It is inducible because allolactase (an isomer of lactose) indirectly induces transcription of the LAC operon.
How is the LAC operon functioning?
When allolactase is available it inactivates the repressor which keeps the LAC operon and therefore lactose degradation in check. The inactive repressor will fall off the operator and induce binding of the RNA polymerase and subsequent transcription of the LAC operon.
What type of operon is the LAC operon?
An inducible operon.
How does positive regulation work for the LAC operon?
When glucose is scarce but lactose is available, cAMP accumulates and binds to a CAP-protein which when bound to cAMP becomes an activator for the LAC operon.
What is differential gene expression?
The expression of different genes by cells with the same genome.
How are eukaryotes regulating their chromatin to influence differential gene expression?
By inducing chemical modifications either on the histones (acetylation) or on the DNA (methylation).
What regulatory effect does acetylation of histones have?
It promotes loosening of the chromatin (euchromatin) and subsequently transcription.
What regulatory effects does methylation of DNA have?
It promotes tightening of chromatin (heterochromatin) and reduced transcription.
What are the three types of regulation at the transcriptional level in eukaryotes?
1. Regulation at the initiation of transcription; 2. splicing; 3. mRNA stability.
How does the cell knows which genes to transcribe and which not to?
By using a specific combination of transcription factors - activators and repressors.
How can eukaryotes carry out differential gene at the splicing step?
By alternative splicing which results in totally different proteins being translated from the same transcribed gene.
Which RNAs are involved in degrading mRNA when unwanted during differential gene expression?
What does microRNA do?
It binds to a target mRNA molecule and tags it for degradation by a protein complex, or for blocked translation.
How is differential gene expression done at the posttranslational level?
By tagging the proteins which must be degraded with ubiquitin, and in this way making them visible for the proteasome.
What is the proteasome?
A protein complex involved in degradation of unwanted/damaged proteins which are usually tagged by ubiquitination.