Directed evolution techniques MCQs With Answer

Directed evolution techniques MCQs With Answer — Introduction

Directed evolution is a cornerstone method in protein engineering, using iterative cycles of mutation and selection to obtain proteins with enhanced properties. This quiz set is designed for M.Pharm students studying Proteins and Protein Formulations, focusing on practical techniques such as error-prone PCR, DNA shuffling, display technologies, library design, screening vs selection, and modern high-throughput methods. Questions emphasize mechanistic understanding, experimental parameters, and interpretation of results relevant to improving activity, stability, specificity, and formulation compatibility. Working through these MCQs will reinforce conceptual depth and prepare students for designing and evaluating directed evolution experiments in pharmaceutical protein development.

Q1. What best defines the core principle of directed evolution in protein engineering?

• Rational design based solely on crystal structures
• Iterative cycles of random mutation and selection for improved function
• Using only computational algorithms to predict optimal sequences
• Stabilizing proteins by chemical cross-linking

Correct Answer: Iterative cycles of random mutation and selection for improved function

Q2. Which parameter is commonly changed in error-prone PCR to increase the mutation rate?

• Lowering Mg2+ concentration and using proofreading polymerase
• Adding Mn2+ and using imbalanced dNTP concentrations
• Increasing annealing temperature and decreasing extension time
• Using restriction enzymes during amplification

Correct Answer: Adding Mn2+ and using imbalanced dNTP concentrations

Q3. What distinguishes DNA shuffling from simple random mutagenesis?

• It introduces only single-nucleotide substitutions
• It recombines homologous gene fragments to create chimeras
• It uses site-directed oligonucleotides exclusively
• It relies on chemical mutagens rather than PCR

Correct Answer: It recombines homologous gene fragments to create chimeras

Q4. What is the aim of site-saturation mutagenesis at a specific residue?

• To replace the residue with only conservative substitutions
• To sample all 20 amino acids at that position to find optimal residue
• To create only stop codons at that position for truncation studies
• To delete the residue and study structural collapse

Correct Answer: To sample all 20 amino acids at that position to find optimal residue

Q5. In phage display, how is the genotype linked to phenotype?

• The protein is synthesized separately from its encoding DNA
• The displayed protein is covalently attached to purified DNA
• The protein is genetically fused to a phage coat protein so the encoding DNA is inside the phage particle
• The protein and gene are linked via a chemical cross-linker

Correct Answer: The protein is genetically fused to a phage coat protein so the encoding DNA is inside the phage particle

Q6. What advantage does ribosome display provide over cell-based display systems?

• It requires cellular transformation and growth
• It allows selection from much larger libraries in a cell-free system
• It mandates post-translational glycosylation for function
• It cannot maintain the mRNA–ribosome–polypeptide complex

Correct Answer: It allows selection from much larger libraries in a cell-free system

Q7. Why might yeast surface display be chosen over bacterial display for evolving therapeutic proteins?

• Yeast display eliminates all post-translational modifications
• Yeast provides eukaryotic folding and glycosylation machinery relevant to therapeutics
• Yeast displays proteins inside the cytoplasm only
• Yeast cannot be analyzed by flow cytometry

Correct Answer: Yeast provides eukaryotic folding and glycosylation machinery relevant to therapeutics

Q8. What is the essential concept behind compartmentalized self-replication (CSR) for enzyme evolution?

• Linking enzyme activity to replication of its encoding gene within micro-compartments
• Using bulk solution without any compartmentalization to select enzymes
• Replicating only plasmid backbone sequences irrespective of enzyme activity
• Selecting enzymes based on precipitation in organic solvents

Correct Answer: Linking enzyme activity to replication of its encoding gene within micro-compartments

Q9. How does a selection differ from a screen in directed evolution experiments?

• A selection requires individual measurement of each variant, screening is survival-based
• A selection enriches functional variants by survival or growth; a screen assays variants individually
• Selection is lower throughput than screening in all cases
• Selections cannot be coupled to sequencing for analysis

Correct Answer: A selection enriches functional variants by survival or growth; a screen assays variants individually

Q10. What is the primary advantage of DNA shuffling in iterative evolution campaigns?

• It guarantees elimination of all deleterious mutations
• It recombines beneficial mutations from different parental sequences to create improved variants
• It only introduces silent mutations to preserve function
• It avoids any changes to the primary sequence

Correct Answer: It recombines beneficial mutations from different parental sequences to create improved variants

Q11. What does deep mutational scanning combine to map sequence-function relationships?

• Random mutagenesis with low-throughput biochemical assays
• Systematic variant library generation with high-throughput selection and next-generation sequencing
• Only computational predictions without experimental data
• Classical Sanger sequencing of a few clones

Correct Answer: Systematic variant library generation with high-throughput selection and next-generation sequencing

Q12. Why is introducing stabilizing mutations often used before evolving new activity?

• Stabilizing mutations always reduce catalytic activity
• Stability increases allow accumulation of activity-enhancing but destabilizing mutations without loss of fold
• Stabilizing mutations make proteins more immunogenic
• Stabilizing mutations make subsequent mutagenesis impossible

Correct Answer: Stability increases allow accumulation of activity-enhancing but destabilizing mutations without loss of fold

Q13. What is the role of mutator strains in in vivo directed evolution?

• They decrease mutation rates to protect the plasmid
• They allow accelerated mutation rates in cells by impairing DNA repair or proofreading
• They are used to maintain plasmid copy number constant
• They convert all point mutations into insertions

Correct Answer: They allow accelerated mutation rates in cells by impairing DNA repair or proofreading

Q14. Which approach gives precise control over which residues are altered at specific positions?

• Error-prone PCR
• Site-directed saturation mutagenesis using designed oligonucleotides
• Random chemical mutagenesis
• UV irradiation of whole cells

Correct Answer: Site-directed saturation mutagenesis using designed oligonucleotides

Q15. What is the basic idea behind consensus design for improving protein stability?

• Selecting the least conserved residues across homologs for substitution
• Replacing residues with the most frequently observed amino acid at each position across homologous sequences
• Introducing random insertions into loops
• Using only hydrophobic residues to replace polar ones

Correct Answer: Replacing residues with the most frequently observed amino acid at each position across homologous sequences

Q16. Which codon degeneracy scheme is commonly used in site-saturation libraries to minimize stop codons while sampling amino acid diversity?

• NNN (all 64 codons equally)
• NNK or NNS (32 codons, reduced stop codon frequency)
• NNR (purine-only codons)
• NNY (pyrimidine-only codons)

Correct Answer: NNK or NNS (32 codons, reduced stop codon frequency)

Q17. How should selection stringency typically be adjusted across multiple rounds of directed evolution?

• Keep stringency constant to avoid bias
• Decrease stringency each round to preserve diversity
• Increase stringency gradually to enrich progressively improved variants
• Randomly alternate high and low stringency irrespective of results

Correct Answer: Increase stringency gradually to enrich progressively improved variants

Q18. Which of the following display methods is entirely cell-free?

• Phage display
• Yeast surface display
• Ribosome display
• Bacterial surface display

Correct Answer: Ribosome display

Q19. Which high-throughput screening technology enables sorting of enzymatic variants encapsulated in droplets at millions per day?

• Plate-based colony picking
• Microfluidic droplet screening with fluorescence-activated droplet sorting
• SDS-PAGE analysis of pooled lysates
• Traditional spectrophotometer endpoint assays on a single sample

Correct Answer: Microfluidic droplet screening with fluorescence-activated droplet sorting

Q20. What does epistasis refer to in the context of protein evolution?

• Mutations that always act independently and additively on activity
• Non-additive interactions between mutations where the combined effect differs from the sum of individual effects
• Only deleterious mutations that are purged by selection
• Mutations that only affect gene expression but not protein function

Correct Answer: Non-additive interactions between mutations where the combined effect differs from the sum of individual effects

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