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What what stages can gene regulation occur and which is the most common?
- Transcription: Most common
- Post translation
What type of protein regulates transcription?
What is a regulatory protein?
Proteins that bind to DNA and affect the rate of transcription of one or more nearby genes.
What are the two most common types of regulatory proteins?
- Repressor (Inhibit)
- Activator (Increases)
What is Negative control?
Transcriptional regulation by repressors.
What is positive control?
Regulation by activators.
What are effector molecules?
Small molecules that does not bind directly to DNA, but rather bind to regulatory proteins (activators & repressors) causing conformational changes in regulatory proteins. These changes make the protein no longer able to bind to DNA.
What is a Ligand?
Any molecule that binds to a specific site on a protein.
What is an inducer?
- A small effector molecule that cause transcription to increase.
- A) Bind to an activator protein causing it to bind to DNA.
- B) Bind to a repressor protein preventing it from binding to DNA.
What is a repressible gene and what are the two types?
- A small effector molecule can inhibit transcription.
- A) Compressor: small molecule that binds to a repressor protein causing the protein to bind to DNA.
- B) Inhibitor: small molecule that binds to activator protein preventing it from binding to the DNA.
What is an Operon?
A few structural genes arranged together in a regulatory unit under the transcriptional control of a single promotor.
What is polycistronic mRNA?
Transcribed from an operon; includes the transcript of two or more structural genes.
Describe the structure of a repressor.
Four subunits each with an allolactose (inducer) binding site.
What is the function of the CAP protein?
Enhances the expression of the lac operon when lactose is present and glucose is absent.
What does the acronym CAP stand for in CAP protein?
Catabolite Activator Protein
What is the affect of cyclic AMP on CAP proteins?
Two cAMP molecules function as allosteric effectors by increaing CAP affinity for DNA. This allows RNA polymerase to bind and transcribe the genes involved in lactose catabolism.
What catalyzes the formation of cAMP from ATP?
What inhibits formation of cAMP?
What is an allosteric enzyme?
- Induces an operon.
- Contains two binding sites.
- Effector binds to the proteins allosteric site, while the active site is bound to DNA.
What is diauxic growth and in the presence of glucose/lactose, which is used first?
- Sequential use of two sugars.
If the lac repressor binds to two of the three operator sites, what happens?
The resulting loop prevents RNA polymerase from recognizing the promoter site.
What is another name for the are Operon?
What happens to the BAD operon in the absence of arabinose?
araC coded proteins bind to operator sites, two of which interact to form a loop that inhibits BAD transcription.
What happens to the BAD operon in the presence of arabinose?
- No glucose, cAMP allows CAP to bind promoting BAD transcription.
- If glucose is present, no cAMP and no binding of CAP and no promoting of BAD transcription.
What is attenuation?
- A secondary regulatory mechanism for trp operon.
- Mediated by the region that includes the trpL gene.
- Can only occur in bacteria because transcription and translation are coupled.
During attenuation of the trp operon mRNA, all four domains coded by the trpL gene can form what?
Different stem-loop structures based upon interactions.
Domain one of the trpL gene codes for what?
This allows bacterium to determine what?
- The leader peptide (14 amino acids) and contains two tryptophan codons.
- If sufficient levels of tryptophan are present in the cell and the need to proceed with transcription.
What happens to the trp operon when tryptophan levels are low?
- Slow translation of domain 1 peptide.
- Domain 2-3 pairing occurs.
- Normal full gene transcription.
What happens to the trp operon when tryptophan levels are high?
- Fast translation of domain 1 peptide.
- Domain 2 blocked by ribosome.
- Domain 3-4 pairing occurs.
- Attenuation of transcription occurs.
- Only 10% of normal mRNAs is made.
Describe the general process of Translational regulation.
Involves inhbiting the initiation of translation using translational repressors. Regulatory proteins recognize sequences of mRNA.
What are the two methods that translational repressors can inhibit translation?
- Bind in the vicinity of Shine-dalgarno sequence and/or start codon & block the ribosome's ability to initiate translation.
- Stabilize mRNA secondary structure preventing initiation of translation.
In addition to translational repressors, translation can be prevented by the synthesis of what?
What is Micro RNA (miRNA)?
- Single-stranded RNA molecules of 21-23 nucleotides in length, which regulate gene expression.
- Mature miRNA molecules are partially complementary to one or more messenger RNA (mRNA) molecules, and their main function is to down-regulate gene expression.
What are the two methods of post translational regulation?
- Negative feed back loop of metabolic pathway's final products.
- Covalently modifying the structure of a protein.
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