Positive control and regulation of protein synthesis MCQs With Answer
Positive control and regulation of protein synthesis are central topics for B.Pharm students, linking molecular biology to pharmacology and drug design. Positive control refers to mechanisms—such as activator proteins, cAMP–CRP, transcription factors and nuclear receptors—that enhance gene expression at transcriptional or translational levels. Regulation of protein synthesis spans operon control in bacteria, chromatin remodeling, coactivator recruitment, mTOR-mediated translation initiation, and post-transcriptional regulators like miRNAs and riboswitches. Understanding these pathways is essential for interpreting antibiotic action, epigenetic therapies, and receptor-targeted drugs. This concise review focuses on molecular mechanisms, physiological examples, and therapeutic implications to reinforce core concepts for exams and practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What best describes “positive control” of gene expression?
- An activator protein that increases transcription initiation
- A repressor that prevents transcription
- A mutation that inactivates RNA polymerase
- An RNA molecule that degrades mRNA
Correct Answer: An activator protein that increases transcription initiation
Q2. In the lac operon, which complex mediates positive control when glucose is low?
- Lac repressor bound to operator
- cAMP–CAP (CRP–cAMP) complex bound upstream of promoter
- Allolactose bound to RNA polymerase
- Ribosome binding to lacZ mRNA
Correct Answer: cAMP–CAP (CRP–cAMP) complex bound upstream of promoter
Q3. Where does CAP (CRP) bind to exert positive control on the lac promoter?
- Within the operator overlapping the promoter
- Upstream at a CRP binding site enhancing RNA polymerase recruitment
- At the ribosome binding site of lacZ mRNA
- Inside the coding region of lacY
Correct Answer: Upstream at a CRP binding site enhancing RNA polymerase recruitment
Q4. How does AraC regulate the arabinose operon under positive control?
- AraC binds DNA only to repress transcription in presence of arabinose
- AraC acts as an activator when bound to arabinose, facilitating RNA polymerase binding
- AraC degrades arabinose to initiate transcription
- AraC methylates promoter DNA to increase expression
Correct Answer: AraC acts as an activator when bound to arabinose, facilitating RNA polymerase binding
Q5. In eukaryotes, positive regulation of transcription commonly involves:
- Transcription factors binding enhancers and recruiting coactivators and chromatin remodelers
- Repressors binding promoters to block polymerase entry
- Riboswitches preventing translation initiation
- DNA methylation exclusively increasing transcription
Correct Answer: Transcription factors binding enhancers and recruiting coactivators and chromatin remodelers
Q6. What is the effect of histone acetylation on transcription?
- Chromatin becomes more condensed and transcription is silenced
- Histone acetylation blocks RNA polymerase binding directly
- Chromatin relaxes, facilitating transcriptional activation
- Acetylation targets histones for degradation
Correct Answer: Chromatin relaxes, facilitating transcriptional activation
Q7. Nuclear receptors (e.g., steroid hormone receptors) function primarily as:
- Ligand-activated transcription factors that positively regulate target genes
- Membrane ion channels controlling transcription indirectly
- RNA helicases involved in splicing
- Proteases that cleave transcription factors
Correct Answer: Ligand-activated transcription factors that positively regulate target genes
Q8. Which class of drugs can increase gene expression by inhibiting histone deacetylases?
- Topoisomerase inhibitors
- HDAC inhibitors
- Beta-lactam antibiotics
- Proteasome inhibitors that degrade transcription factors
Correct Answer: HDAC inhibitors
Q9. Activation of mTOR signaling positively regulates protein synthesis by:
- Phosphorylating eIF2 to block initiation
- Enhancing eIF4E availability and cap-dependent translation initiation
- Cleaving rRNA to stop translation
- Exporting mRNAs out of the nucleus
Correct Answer: Enhancing eIF4E availability and cap-dependent translation initiation
Q10. Which antibiotic binds the 50S ribosomal subunit and inhibits peptidyl transferase activity?
- Tetracycline
- Chloramphenicol
- Streptomycin
- Tunicamycin
Correct Answer: Chloramphenicol
Q11. Tetracycline inhibits bacterial protein synthesis by:
- Blocking peptidyl transferase on 50S subunit
- Binding the 30S subunit and preventing aminoacyl-tRNA entry into the A site
- Causing mRNA misreading and faulty proteins
- Inhibiting transcription initiation
Correct Answer: Binding the 30S subunit and preventing aminoacyl-tRNA entry into the A site
Q12. Aminoglycoside antibiotics (e.g., streptomycin) primarily act by:
- Blocking tRNA entry into the A site
- Inducing misreading of mRNA leading to aberrant proteins
- Inhibiting DNA replication
- Acetylating histones to increase expression
Correct Answer: Inducing misreading of mRNA leading to aberrant proteins
Q13. Macrolide antibiotics (e.g., erythromycin) inhibit protein synthesis by:
- Binding 30S subunit and inhibiting initiation
- Blocking the peptide exit tunnel on the 50S subunit and inhibiting elongation
- Targeting eukaryotic ribosomes selectively
- Promoting premature termination via RF proteins
Correct Answer: Blocking the peptide exit tunnel on the 50S subunit and inhibiting elongation
Q14. A positive feedback loop in gene regulation refers to:
- A gene product that enhances its own expression
- A repressor that inhibits its own synthesis
- RNA interference reducing mRNA levels
- An operon that is constitutively off
Correct Answer: A gene product that enhances its own expression
Q15. The primary role of sigma factors in bacteria is:
- Degrading mRNA after translation
- Directing RNA polymerase to specific promoter sequences
- Transporting proteins across membranes
- Acetylating histones to open chromatin
Correct Answer: Directing RNA polymerase to specific promoter sequences
Q16. A typical two-component regulatory system contains which components?
- DNA polymerase and helicase
- Sensor histidine kinase and a response regulator that can act as transcription activator
- Ribosomal protein and tRNA synthetase
- Small interfering RNA and Dicer
Correct Answer: Sensor histidine kinase and a response regulator that can act as transcription activator
Q17. How can a riboswitch act as a positive regulator of translation?
- Ligand binding causes formation of a terminator hairpin that halts transcription
- Ligand binding exposes the ribosome binding site, promoting translation initiation
- Riboswitches only function to repress translation
- Riboswitches methylate mRNA to block translation
Correct Answer: Ligand binding exposes the ribosome binding site, promoting translation initiation
Q18. MicroRNAs (miRNAs) typically regulate gene expression by:
- Enhancing translation of target mRNAs
- Promoting mRNA degradation or repressing translation of target mRNAs
- Directly binding to DNA promoters to increase transcription
- Acting as chaperones for protein folding
Correct Answer: Promoting mRNA degradation or repressing translation of target mRNAs
Q19. What defines a transcriptional coactivator?
- A protein that binds DNA and blocks transcription
- A protein that does not bind DNA directly but bridges activators and the transcriptional machinery
- An RNA polymerase subunit that degrades mRNA
- A histone variant that always represses transcription
Correct Answer: A protein that does not bind DNA directly but bridges activators and the transcriptional machinery
Q20. Which statement about enhancers is true?
- Enhancers must be immediately adjacent to the promoter and oriented in one direction
- Enhancers function independent of orientation and can act at a distance to increase transcription
- Enhancers only operate in prokaryotes
- Enhancers are small RNAs that inhibit translation
Correct Answer: Enhancers function independent of orientation and can act at a distance to increase transcription
Q21. Promoter-proximal elements in eukaryotes are typically located:
- Within the coding sequence of genes
- Approximately within 200 base pairs upstream of the transcription start site
- Only downstream of the poly(A) site
- Exclusively inside introns
Correct Answer: Approximately within 200 base pairs upstream of the transcription start site
Q22. Internal ribosome entry sites (IRES) enable positive regulation of translation under stress by:
- Blocking cap-dependent initiation so translation stops
- Allowing cap-independent initiation on specific mRNAs when cap-dependent initiation is inhibited
- Promoting mRNA splicing
- Recruiting ribonucleases to degrade mRNA
Correct Answer: Allowing cap-independent initiation on specific mRNAs when cap-dependent initiation is inhibited
Q23. Which statement correctly describes attenuation in bacterial operons like trp?
- Attenuation is a form of positive control that increases transcription in high amino acid conditions
- Attenuation couples translation of a leader peptide to transcription termination and is typically negative control
- Attenuation methylates the promoter to activate transcription
- Attenuation functions only in eukaryotes
Correct Answer: Attenuation couples translation of a leader peptide to transcription termination and is typically negative control
Q24. An activation domain of a transcription factor is often characterized by:
- A DNA-binding helix-turn-helix motif
- A region rich in acidic or glutamine residues that recruits coactivators
- A transmembrane helix anchoring the factor to membranes
- A catalytic kinase domain that phosphorylates RNA
Correct Answer: A region rich in acidic or glutamine residues that recruits coactivators
Q25. Which post-translational modification commonly increases transcription factor activity?
- Ubiquitination leading to immediate degradation
- Phosphorylation that alters localization or interaction with coactivators
- Glycosylation of nuclear DNA
- DNA methylation of transcription factor proteins
Correct Answer: Phosphorylation that alters localization or interaction with coactivators
Q26. A practical pharmacological strategy to positively modulate gene expression is:
- Designing agonists for nuclear receptors to activate target gene transcription
- Using broad-spectrum antibiotics to increase transcription globally
- Blocking ribosome assembly to elevate translation
- Inhibiting all histone acetyltransferases to open chromatin
Correct Answer: Designing agonists for nuclear receptors to activate target gene transcription
Q27. High glucose levels affect lac operon positive control by:
- Increasing intracellular cAMP and enhancing CAP binding
- Decreasing cAMP levels, reducing CAP binding and lowering lac expression
- Mimicking allolactose to activate the lac repressor
- Directly phosphorylating RNA polymerase to increase transcription
Correct Answer: Decreasing cAMP levels, reducing CAP binding and lowering lac expression
Q28. Which sigma factor requires specialized activator proteins and ATP hydrolysis to form an open complex?
- Sigma70 (primary housekeeping sigma)
- Sigma54 (RpoN), which often requires activator ATPases for transcription initiation
- Sigma32 (heat shock sigma) that acts independently of activators
- Sigma28 involved in flagellar synthesis that does not require activators
Correct Answer: Sigma54 (RpoN), which often requires activator ATPases for transcription initiation
Q29. During elongation, the A site of the ribosome is primarily responsible for:
- Peptide bond formation between growing chain and incoming tRNA
- Entry of aminoacyl-tRNA matching the codon in mRNA
- Exit of deacylated tRNA from the ribosome
- Binding of release factors to terminate translation
Correct Answer: Entry of aminoacyl-tRNA matching the codon in mRNA
Q30. Which enzyme catalyzes histone acetylation, a mark associated with positive regulation of transcription?
- Histone deacetylase (HDAC)
- Histone acetyltransferase (HAT)
- DNA methyltransferase (DNMT)
- RNA polymerase II
Correct Answer: Histone acetyltransferase (HAT)
