Microbial transformation of steroids MCQs With Answer

Microbial transformation of steroids is a vital topic in bioprocess engineering for M.Pharm students, linking microbiology, enzymology and pharmaceutical synthesis. This blog-style quiz focuses on key concepts such as regio- and stereoselective hydroxylations, dehydrogenations, side-chain degradation, enzyme classes (especially cytochrome P450s and hydroxysteroid dehydrogenases), whole-cell versus isolated enzyme systems, cofactor regeneration, process parameters, scale-up challenges and analytical monitoring. The questions are designed to deepen understanding of mechanisms, commonly used microorganisms, reactor considerations and downstream implications for drug development. Use these MCQs to test and reinforce practical knowledge needed to design, optimize and evaluate microbial steroid biotransformations in research and industry.

Q1. What best describes microbial transformation of steroids?

• Abiotic chemical modification of steroid molecules using catalysts
• Microbial-mediated modification of steroid structures by specific enzymes
• Physical separation of steroid isomers using chromatography
• Synthetic organic chemistry routes to build steroid skeletons

Correct Answer: Microbial-mediated modification of steroid structures by specific enzymes

Q2. Which enzyme class is most commonly responsible for regioselective hydroxylation of steroid substrates?

• Glutathione S-transferases
• Cytochrome P450 monooxygenases
• Proteases
• Kinases

Correct Answer: Cytochrome P450 monooxygenases

Q3. What is a primary advantage of whole-cell biotransformation over isolated enzyme systems for steroid modifications?

• Absolute absence of side reactions
• Built-in cofactor regeneration and native metabolic support
• Unlimited substrate concentration tolerance
• Faster chromatographic purification

Correct Answer: Built-in cofactor regeneration and native metabolic support

Q4. Which genera of microorganisms are frequently employed for fungal-mediated steroid hydroxylation and functionalization?

• Cunninghamella, Rhizopus and Aspergillus
• Escherichia, Salmonella and Shigella
• Lactobacillus, Streptococcus and Bifidobacterium
• Pseudomonas, Acinetobacter and Vibrio

Correct Answer: Cunninghamella, Rhizopus and Aspergillus

Q5. Which genus is widely reported for performing 11α-hydroxylation of steroid substrates?

• Bacillus
• Rhizopus
• Clostridium
• Streptococcus

Correct Answer: Rhizopus

Q6. Which analytical technique is most suitable for sensitive identification and quantitation of steroid biotransformation products?

• UV-visible spectrophotometry without separation
• Liquid chromatography coupled with mass spectrometry (LC-MS/MS)
• Simple gravimetric analysis
• Paper chromatography

Correct Answer: Liquid chromatography coupled with mass spectrometry (LC-MS/MS)

Q7. What is a common cofactor regeneration strategy used in enzymatic steroid hydroxylations?

• Direct addition of stoichiometric NADPH to the reaction
• Use of enzymatic systems like glucose-6-phosphate dehydrogenase to regenerate NADPH
• Replacing NADPH with ATP
• Removing oxygen from the reaction to preserve cofactors

Correct Answer: Use of enzymatic systems like glucose-6-phosphate dehydrogenase to regenerate NADPH

Q8. High stereoselectivity in microbial steroid transformations is primarily determined by which factor?

• Temperature of incubation only
• Active site geometry and enzyme-substrate interactions
• Concentration of inorganic salts
• Method of solvent extraction after reaction

Correct Answer: Active site geometry and enzyme-substrate interactions

Q9. Immobilization of whole cells or enzymes in steroid biotransformations typically provides which practical benefit?

• Increased rate of spontaneous chemical degradation
• Improved operational stability and reusability
• Complete elimination of cofactor requirements
• Unlimited substrate solubility

Correct Answer: Improved operational stability and reusability

Q10. Which bacterial genus is well known for steroid side-chain degradation (cholesterol catabolism) relevant to pharmaceutical steroid modification?

• Mycobacterium
• Lactococcus
• Enterococcus
• Clostridium

Correct Answer: Mycobacterium

Q11. A major formulation and process challenge when performing microbial transformation of steroidal substrates is:

• High water solubility of steroids leading to washout
• Poor aqueous solubility of steroids requiring solubilization strategies
• Excessively high vapor pressure of steroid substrates
• Spontaneous polymerization in water

Correct Answer: Poor aqueous solubility of steroids requiring solubilization strategies

Q12. Which of the following co-solvents is commonly used in small percentages to improve steroid solubility without inactivating biocatalysts?

• Hexane at 50% v/v
• DMSO or ethanol at low (≤5–10%) concentrations
• Concentrated sulfuric acid
• Pure acetone at 100% v/v

Correct Answer: DMSO or ethanol at low (≤5–10%) concentrations

Q13. Hydroxysteroid dehydrogenases (HSDs) participate in steroid biotransformations by catalyzing which type of reaction?

• Hydroxylation of aliphatic side chains requiring oxygen
• Oxidation–reduction interconversion between hydroxyl and keto groups
• Peptide bond cleavage in steroid-peptide conjugates
• Phosphorylation of steroid hydroxyl groups

Correct Answer: Oxidation–reduction interconversion between hydroxyl and keto groups

Q14. The conversion of a Δ5(3β)-hydroxysteroid to a Δ4(3-ketosteroid) (Δ5→Δ4 isomerization and oxidation) is typically catalyzed by which enzyme activity?

• 3β-Hydroxysteroid dehydrogenase/Δ5–Δ4 isomerase
• Lipase
• DNA polymerase
• Chitinase

Correct Answer: 3β-Hydroxysteroid dehydrogenase/Δ5–Δ4 isomerase

Q15. To favor stereospecific 17β-reduction of a 17-ketosteroid using microbial biotransformation, a process engineer would most usefully:

• Heat the culture to 90 °C to speed the reaction
• Select a microorganism known to express stereospecific 17β-hydroxysteroid dehydrogenase
• Add proteases to the reaction to degrade competing enzymes
• Perform the reaction in an anaerobic chamber exclusively

Correct Answer: Select a microorganism known to express stereospecific 17β-hydroxysteroid dehydrogenase

Q16. Which bioreactor parameter is most critical for P450-mediated steroid hydroxylations?

• Dissolved oxygen concentration
• Magnetic field strength
• Light wavelength across the vessel
• Ambient room humidity only

Correct Answer: Dissolved oxygen concentration

Q17. During scale-up of a microbial steroid modification process, a frequent limiting factor is:

• Unlimited oxygen transfer at large volumes
• Substrate and product toxicity leading to inhibition of biocatalyst activity
• Inability to maintain sterile conditions at small scale
• Complete elimination of by-product formation

Correct Answer: Substrate and product toxicity leading to inhibition of biocatalyst activity

Q18. An effective genetic engineering strategy to improve steroid hydroxylation yield in a microbial host would be:

• Knocking out all native P450 genes to reduce competition
• Co-expressing a target P450 monooxygenase with NADPH-regenerating enzymes
• Deleting all membrane transporters to trap substrates outside the cell
• Overexpressing random transcription factors without targets

Correct Answer: Co-expressing a target P450 monooxygenase with NADPH-regenerating enzymes

Q19. Which downstream processing concern is particularly important for steroid products from microbial biotransformations intended for pharmaceuticals?

• Ensuring removal of microbial endotoxins and validating impurity profile
• Leaving whole-cell debris in the final formulation for stability
• Maximizing residual solvent content to improve potency
• Neglecting stereochemical purity because it is irrelevant

Correct Answer: Ensuring removal of microbial endotoxins and validating impurity profile

Q20. Which strategy can increase regioselectivity and yield in steroid biotransformations without changing the microorganism?

• Altering substrate structure via protecting groups or side-chain modifications
• Completely randomizing incubation temperature every hour
• Adding high concentrations of denaturing agents
• Using excessive mechanical shear to lyse cells

Correct Answer: Altering substrate structure via protecting groups or side-chain modifications

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