Topic 8 - Regulation - Clickers Flashcards
What binds to this region?
a) ATP
b) Ribosome
c) Rho protein
d) RNA polymerase
e) DNA polymerase
d) RNA polymerase
Explanation: RNA polymerase binds to the promoter region (indicated by the -35 and -10 sequences) to initiate transcription. This interaction allows RNA polymerase to position itself correctly to begin RNA synthesis at the +1 site.
Number from left to right.
____ promoter
____ leader
____ operator
____ activator binding site
2 promoter
4 leader
3 operator
1 activator binding site
When repellant concentrations increase for a motile cell, ________________. (choose all that apply)
a) CheR will continue to methylate the MCPs
b) CheA will become phosphorylated
c) CheB-P will begin demethylating the MCPs
d) CheY-P will cause the flagella to rotate in a clockwise rotation (tumble)
All answers are correct:
CheR methylating MCPs: CheR constitutively methylates methyl-accepting chemotaxis proteins (MCPs), irrespective of repellant presence, modulating their sensitivity to repellants.
CheA phosphorylation: When repellants bind to MCPs, they cause a conformational change that activates CheA, leading to its phosphorylation.
CheB-P demethylating MCPs: Phosphorylated CheA transfers a phosphate group to CheB, activating it (CheB-P). CheB-P counteracts CheR by demethylating MCPs, modulating the chemotaxis response.
CheY-P inducing tumbling: Phosphorylated CheA transfers its phosphate to CheY, activating CheY-P. CheY-P interacts with the flagellar motor, causing it to rotate clockwise, resulting in a tumble to reorient the cell.
When attractant concentrations increase for a motile cell, ________________. (choose all that apply)
a) CheR will continue to methylate the MCPs
b) CheB-P will begin demethylating the MCPs
c) CheY-P will cause the flagella to rotate in a clockwise rotation (tumble)
d) CheA will become phosphorylated
a) CheR will continue to methylate the MCPs
Explanation: CheR is a constitutive enzyme that continuously methylates methyl-accepting chemotaxis proteins (MCPs). Its activity is independent of whether attractants or repellants are present. The methylation by CheR modulates the sensitivity of MCPs to attractants, helping the cell adapt to prolonged exposure to attractant gradients.
When attractant concentrations remain constant for a motile cell, ________________. (choose all that apply)
a) CheA will become phosphorylated
b) CheR will continue to methylate the MCPs
c) CheY-P will cause the flagella to rotate in a clockwise rotation (tumble)
d) CheB-P will begin demethylating the MCPs
All answers are correct:
CheA phosphorylation (a): CheA activity is maintained at a basal level when attractant concentrations remain constant, allowing phosphorylation to occur intermittently. This provides a balanced response to avoid overadaptation.
CheR methylating MCPs (b): CheR continuously methylates MCPs to maintain their sensitivity. Even under constant attractant levels, this process continues to adapt receptor signaling.
CheY-P inducing tumbling (c): CheA phosphorylates CheY, creating CheY-P, which interacts with the flagellar motor to induce occasional tumbling. This ensures the cell does not become trapped in one direction.
CheB-P demethylating MCPs (d): CheB is phosphorylated by CheA to become CheB-P, balancing the methylation by CheR by demethylating MCPs. This regulation prevents overstimulation or desensitization to attractants.
When repellant concentrations decrease for a motile cell as it runs, ______________ (choose all that apply).
a) CheA will become phosphorylated
b) CheB-P will begin demethylating the MCPs
c) CheR will continue to methylate the MCPs
d) CheY-P will cause the flagella to rotate in a clockwise rotation (tumble)
e) Sensitivity to repellants will go up
c) CheR will continue to methylate the MCPs;
e) Sensitivity to repellants will go up
Explanation:
CheR will continue to methylate the MCPs (c): CheR is a constitutive enzyme that methylates MCPs continuously, irrespective of repellant concentrations. This ensures that MCPs adapt to the environmental changes and maintain a baseline activity.
Sensitivity to repellants will go up (e): As repellant concentrations decrease, the demethylation activity of CheB-P slows down, allowing MCPs to retain more methyl groups added by CheR. This increased methylation heightens MCP sensitivity to future repellant signals, ensuring the cell can quickly detect changes in the environment.
Which of the following features can occur multiple times on the same mRNA strand in bacteria? Choose all that apply.
a) start codons
b) stop codons
c) structural genes
d) Shine-Dalgarno sequences
All of the answers can occur multiple times on the same mRNA strand in bacteria.
Explanation: Bacterial mRNAs are often polycistronic, meaning they contain multiple structural genes. Each gene is preceded by its own Shine-Dalgarno sequence for ribosome binding and start codon, and followed by a stop codon to terminate translation of that gene.
Which of the following is NOT a characteristic of bacterial transcription?
a) terminator loops
b) sigma factors
c) polycistronic
d) introns
e) rho proteins
d) introns
Explanation: Bacterial transcription does not involve introns; introns are characteristic of eukaryotic transcription where they are spliced out during mRNA processing.
Repression of transcription is usually associated with ______ pathways.
a) anabolic
b) catabolic
a) anabolic
Explanation: Repression of transcription is typically associated with anabolic pathways to conserve energy when the end product is sufficient.
Wikipedia: “In bacteria that synthesize tryptophan, high cellular levels of this amino acid binds a ______, which binds to the [operator].”
a) activator
b) promoter
c) co-repressor
d) repressor
e) co-activator
c) co-repressor
Explanation: Tryptophan acts as a co-repressor, enabling the repressor protein to bind to the operator and block transcription.
Bacterial operons may be under positive or negative control of transcription, never both.
a) True
b) False
b) False
Explanation: Bacterial operons can exhibit both positive and negative control depending on regulatory needs.
Induction is still negative control of transcription because an operator-binding repressor protein is involved.
a) True
b) False
a) True
Explanation: Induction relies on removing the operator-bound repressor, classifying it as negative control.
Operons with promoters that bind RNA polymerase weakly are likely under what form of regulatory control?
a) positive
b) negative
a) positive
Explanation: Positive control mechanisms often enhance RNA polymerase binding to weak promoters.
cAMP is bound to the cAMP receptor protein (CRP). This means that __________.
a) lactose is high
b) glucose is low
c) lactose is low
d) glucose is high
b) glucose is low
Explanation: cAMP-CRP binding occurs under low glucose conditions, signaling the need for alternative carbon sources.
cAMP is bound to the cAMP receptor protein (CRP). This means that __________.
a) transcription proceeds
b) don’t know
c) transcription is repressed
a) transcription proceeds
Explanation: cAMP-CRP facilitates transcription of genes necessary for utilizing non-glucose carbon sources.
If there is excess tryptophan available in Escherichia coli, which of the following is/are likely to happen?
a) tryptophan structural genes are transcribed
b) slow translation: 2-3 stem loop forms, transcription termination occurs
c) fast translation: 3-4 stem loop forms, transcription termination occurs
d) tryptophan structural genes translated
c) fast translation: 3-4 stem loop forms, transcription termination occurs
Explanation: In the presence of excess tryptophan, ribosomes quickly translate the leader peptide, causing the 3-4 stem loop to form and terminate transcription of the tryptophan operon.
Attenuation occurs in the biosynthetic pathway for phenylalanine in Escherichia coli. Therefore, the leader sequence for this pathway will be rich in which of the following?
a) threonine
b) isoleucine
c) tryptophan
d) phenylalanine
e) histidine
d) phenylalanine
Explanation: The leader sequence for phenylalanine biosynthesis contains codons rich in phenylalanine to sense its abundance and regulate operon transcription accordingly.
Which of the following statements is/are FALSE about two-component regulatory systems?
a) Involves a response regulator
b) Involves a sensor kinase
c) Phosphorylation of the response regulator is required for regulation of transcription
d) A single response regulator can either be an activator or a repressor, never both
e) The response regulator can possibly dephosphorylate itself
d) A single response regulator can either be an activator or a repressor, never both
Explanation: This statement is false because response regulators in two-component systems can function as both activators and repressors, depending on the operon or genes they regulate. For example, in some cases, the phosphorylated response regulator activates transcription, while in others, it represses transcription by binding to operator regions. This versatility allows efficient regulation of diverse cellular responses.
For E. coli, in the presence of lactose, __________.
a) a co-inducer binds to the lac repressor protein
b) the lac operon will be transcribed
c) the lac repressor binds to the operator
d) genes of the lac operon are not expressed
a) a co-inducer binds to the lac repressor protein
Explanation: In the presence of lactose, allolactose (a co-inducer) binds to the lac repressor, preventing it from binding to the operator and allowing transcription of the lac operon.
For the lac operon, the co-inducer is __________.
a) acyl homoserine lactones (AHLs)
b) cAMP
c) allolactose
d) glucose
e) lactose
c) allolactose
Explanation: Allolactose, a derivative of lactose, serves as the co-inducer for the lac operon, binding to the lac repressor and inhibiting its activity.
Where would you NOT find attenuation?
a) Pseudomonas
b) Nanoarchaeota
c) Micrococcus
d) Chlamydomonas
e) Chromatium
d) Chlamydomonas
Explanation: Attenuation is found in bacteria and archaea, but not in eukaryotic organisms like Chlamydomonas.
Quorum sensing can be described as ______.
a) the regulation of gene expression based on population density
b) negative feedback
c) a relatively rare adaptation for bacteria-eukaryote symbioses
d) constitutive expression of essential genes
a) the regulation of gene expression based on population density
Explanation: Quorum sensing involves bacteria detecting and responding to changes in population density by regulating gene expression.
Quorum sensing in Aliivibrio fischeri is an example of __________.
a) attenuation
b) negative control of transcription
c) positive control of transcription
d) allosteric enzyme inhibition
c) positive control of transcription
Explanation: In Aliivibrio fischeri, quorum sensing activates transcription of genes required for bioluminescence, exemplifying positive control.
