Expression vectors MCQs With Answer

Introduction:

This quiz collection on Expression Vectors is designed for M.Pharm students studying Advanced Pharmaceutical Biotechnology. It focuses on the principles, components, and applications of expression vectors used for recombinant protein production across bacterial, yeast, insect, and mammalian systems. The questions emphasize vector architecture (promoters, origins, selection markers), regulation (inducible vs constitutive), host compatibility, fusion tags, secretion signals, and specialized viral and shuttle vectors. These MCQs aim to deepen conceptual understanding, support exam preparation, and build practical insight into choosing and designing vectors for therapeutic protein expression, vaccine development, and biopharmaceutical research.

Q1. Which element in a prokaryotic expression vector directly determines the initiation of translation by aligning the ribosome with the start codon?

• Origin of replication
• Promoter
• Shine-Dalgarno sequence
• Polyadenylation signal

Correct Answer: Shine-Dalgarno sequence

Q2. Which promoter is most commonly used in E. coli systems for very strong, T7 RNA polymerase-driven expression?

• lac promoter
• T7 promoter
• CMV promoter
• AOX1 promoter

Correct Answer: T7 promoter

Q3. What is the primary purpose of including a fusion tag such as 6xHis or GST in an expression vector?

• To increase plasmid replication rate
• To facilitate protein purification and detection
• To drive high-level transcription
• To enhance mRNA stability in the nucleus

Correct Answer: To facilitate protein purification and detection

Q4. Which vector feature is most critical for maintaining plasmid copy number control in E. coli?

• Selectable marker gene
• Origin of replication
• Promoter strength
• Polylinker (multiple cloning site)

Correct Answer: Origin of replication

Q5. In yeast expression systems like Pichia pastoris, which promoter is commonly used for methanol-inducible expression?

• GAP promoter
• AOX1 promoter
• GAL1 promoter
• TEF1 promoter

Correct Answer: AOX1 promoter

Q6. Which of the following is an advantage of using a secretory signal peptide (e.g., pelB) in a bacterial expression vector?

• Increase plasmid copy number
• Direct protein to the periplasm or extracellular space to aid folding and disulfide bond formation
• Reduce promoter leakiness
• Enhance ribosome binding site strength

Correct Answer: Direct protein to the periplasm or extracellular space to aid folding and disulfide bond formation

Q7. Which selection marker is suitable for mammalian expression vectors when antibiotic selection in culture is required?

• bla (ampicillin resistance)
• kanR (kanamycin resistance)
• neo (neomycin/G418 resistance)
• ura3 (uracil auxotrophy)

Correct Answer: neo (neomycin/G418 resistance)

Q8. What role does a Kozak sequence play in eukaryotic expression vectors?

• Acts as an origin of replication in mammalian cells
• Enhances ribosome recognition of the start codon for efficient translation initiation
• Promotes mRNA polyadenylation
• Encodes a secretion signal

Correct Answer: Enhances ribosome recognition of the start codon for efficient translation initiation

Q9. Why are inducible promoters, such as lac, araBAD, or tetracycline-regulated systems, preferred for expressing toxic proteins?

• They permanently silence the host genome
• They allow temporal control of expression to minimize host toxicity prior to induction
• They increase plasmid copy number automatically
• They promote secretion of the toxic protein

Correct Answer: They allow temporal control of expression to minimize host toxicity prior to induction

Q10. Which viral vector is most commonly used for stable integration and long-term expression in dividing and non-dividing mammalian cells?

• Adenoviral vector
• Adeno-associated virus (AAV)
• Lentiviral vector
• Baculovirus vector

Correct Answer: Lentiviral vector

Q11. In vector design, what is the main purpose of including a protease cleavage site (e.g., TEV or thrombin) between a fusion tag and the target protein?

• To increase plasmid replication efficiency
• To allow removal of the tag after purification, yielding the native protein sequence
• To enhance promoter-driven transcription
• To target the protein to mitochondria

Correct Answer: To allow removal of the tag after purification, yielding the native protein sequence

Q12. Which feature distinguishes a shuttle vector from a standard plasmid vector?

• Presence of a strong prokaryotic promoter only
• Capability to replicate in two different host species due to dual origins of replication
• Exclusive use of viral promoters for expression
• Inability to be selected with antibiotics

Correct Answer: Capability to replicate in two different host species due to dual origins of replication

Q13. For high-yield expression of a secreted glycoprotein requiring complex post-translational modifications, which host-vector system is most appropriate?

• E. coli expression vector
• Saccharomyces cerevisiae with cytosolic expression
• Mammalian expression vector (e.g., CHO cells with CMV promoter)
• Pseudomonas expression system

Correct Answer: Mammalian expression vector (e.g., CHO cells with CMV promoter)

Q14. What is the function of an internal ribosome entry site (IRES) in bicistronic eukaryotic expression vectors?

• To terminate transcription prematurely
• To allow cap-independent translation initiation of a downstream open reading frame
• To increase plasmid copy number
• To add a secretion signal to the second protein

Correct Answer: To allow cap-independent translation initiation of a downstream open reading frame

Q15. Which component is essential in an expression vector intended for high-fidelity expression of small peptides prone to proteolysis in E. coli?

• Strong ribosome binding site with no fusion tag
• High-copy origin with no selection marker
• N-terminal fusion partner (e.g., MBP or SUMO) to enhance solubility and protect from proteases
• Removal of any transcription terminator

Correct Answer: N-terminal fusion partner (e.g., MBP or SUMO) to enhance solubility and protect from proteases

Q16. Which attribute of an expression vector would you modify to reduce basal (leaky) expression from an inducible promoter?

• Remove the origin of replication
• Introduce a stronger ribosome binding site
• Add a transcriptional repressor/operator system or use tighter repressor variants
• Increase promoter copy number

Correct Answer: Add a transcriptional repressor/operator system or use tighter repressor variants

Q17. For generating recombinant protein with human-like N-linked glycosylation, which expression system and associated vector choice is most suitable?

• E. coli plasmid expression
• Insect cell baculovirus system without glycoengineering
• Mammalian expression vector in CHO or HEK293 cells
• Plant expression vector in tobacco with no modification

Correct Answer: Mammalian expression vector in CHO or HEK293 cells

Q18. What is a primary safety consideration when using integrative viral vectors (e.g., gamma-retroviral) for therapeutic gene delivery?

• Excessive plasmid copy number in bacteria
• Risk of insertional mutagenesis activating oncogenes or disrupting tumor suppressors
• Inability to package large genes
• Lack of promoters for eukaryotic expression

Correct Answer: Risk of insertional mutagenesis activating oncogenes or disrupting tumor suppressors

Q19. Which strategy is commonly used in vector design to improve translation efficiency by matching codon usage to the host organism?

• Adding multiple cloning sites
• Codon optimization of the coding sequence for the expression host
• Using viral promotors exclusively
• Increasing plasmid size

Correct Answer: Codon optimization of the coding sequence for the expression host

Q20. When designing an expression vector for endotoxin-sensitive applications, which host and vector modifications are preferable?

• Use E. coli with high LPS strains and strong T7 promoter
• Use Gram-positive hosts (e.g., Bacillus) or endotoxin-free E. coli strains and include secretion to reduce endotoxin in product
• Use yeast without secretion signals
• Use adenoviral vectors produced in HEK293 with no purification

Correct Answer: Use Gram-positive hosts (e.g., Bacillus) or endotoxin-free E. coli strains and include secretion to reduce endotoxin in product

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