Biosynthetic pathways of secondary metabolites MCQs With Answer

Biosynthetic pathways of secondary metabolites MCQs With Answer

This question set is designed for M.Pharm students studying Bioprocess Engineering and Technology. It focuses on the enzymatic routes and molecular logic that generate secondary metabolites such as polyketides, nonribosomal peptides, terpenoids and aromatic compounds. Questions emphasize pathway building blocks (e.g., malonyl‑CoA, IPP, chorismate), catalytic domains (PKS/NRPS modules, P450s, glycosyltransferases), regulation, gene clusters and experimental approaches used in pathway elucidation and engineering. These MCQs go beyond basic facts to explore mechanism, pathway engineering challenges and analytical strategies, helping students prepare for exams and practical applications in strain improvement and heterologous expression.

Q1. Which extender unit is most commonly incorporated during polyketide chain elongation by type I PKSs?

• Malonyl‑CoA
• Acetyl‑CoA
• S‑adenosylmethionine
• Isopentenyl pyrophosphate

Correct Answer: Malonyl‑CoA

Q2. Which feature best describes type I modular polyketide synthases (PKSs)?

• Large multifunctional modular enzymes operating in an assembly‑line manner
• Small discrete enzymes that iterate repeatedly
• Single active site enzymes producing aromatic polyketides
• RNA‑templated peptide synthases

Correct Answer: Large multifunctional modular enzymes operating in an assembly‑line manner

Q3. In nonribosomal peptide synthetases (NRPS), which domain selects and activates specific amino acids?

• Peptidyl carrier protein (PCP) domain
• Condensation domain
• Adenylation domain
• Thioesterase domain

Correct Answer: Adenylation domain

Q4. Which enzyme catalyzes the committed and rate‑limiting step of the mevalonate pathway?

• HMG‑CoA reductase
• Mevalonate kinase
• Isopentenyl diphosphate isomerase
• Geranyl diphosphate synthase

Correct Answer: HMG‑CoA reductase

Q5. What is the immediate end product of the shikimate pathway that serves as a branch point for aromatic secondary metabolites?

• Shikimate
• Chorismate
• Prephenate
• Phenylalanine

Correct Answer: Chorismate

Q6. Which type of polyketide synthase is typically responsible for biosynthesis of bacterial aromatic polyketides?

• Type I modular PKS
• Type II iterative PKS
• Type III chalcone synthase‑like PKS
• Type IV radical PKS

Correct Answer: Type II iterative PKS

Q7. Which domain is primarily responsible for releasing the fully assembled product from a PKS or NRPS assembly line?

• Acyl carrier protein (ACP)
• Ketosynthase (KS)
• Thioesterase (TE) domain
• Dehydratase (DH)

Correct Answer: Thioesterase (TE) domain

Q8. What is the main biochemical role of S‑adenosylmethionine (SAM) in secondary metabolism?

• Methyl group donor for methyltransferases
• Universal glycosyl donor
• Adenylation cofactor for NRPS
• Electron donor for monooxygenases

Correct Answer: Methyl group donor for methyltransferases

Q9. Which enzyme family frequently carries out regio‑ and stereoselective hydroxylation steps during tailoring of secondary metabolites?

• Glycosyltransferases
• Cytochrome P450 monooxygenases
• Methyltransferases
• Thioesterases

Correct Answer: Cytochrome P450 monooxygenases

Q10. Which is the non‑mevalonate pathway for isoprenoid biosynthesis commonly found in many bacteria and plant plastids?

• MEP (2‑C‑methyl‑D‑erythritol 4‑phosphate) pathway
• Mevalonate pathway
• Shikimate pathway
• Polyketide pathway

Correct Answer: MEP (2‑C‑methyl‑D‑erythritol 4‑phosphate) pathway

Q11. What is the primary functional role of the acyl carrier protein (ACP) in polyketide biosynthesis?

• Provides an active site cysteine for chain elongation
• Carries the growing acyl chain via a 4’‑phosphopantetheine arm
• Forms the cyclized aromatic core by aldol condensation
• Hydrolyzes the final product from the enzyme complex

Correct Answer: Carries the growing acyl chain via a 4’‑phosphopantetheine arm

Q12. How are D‑amino acids commonly introduced into nonribosomal peptides?

• Direct incorporation by ribosomes
• Oxidative deamination during tailoring
• Epimerization domain within NRPS modules
• Spontaneous racemization of L‑amino acids

Correct Answer: Epimerization domain within NRPS modules

Q13. What distinguishes hybrid PKS‑NRPS biosynthetic pathways?

• Exclusive use of malonyl‑CoA as all building blocks
• Modular enzymes that combine polyketide and peptide modules in one assembly line
• Production of only terpenoid compounds
• Ribosomal synthesis followed by extensive post‑translational modification

Correct Answer: Modular enzymes that combine polyketide and peptide modules in one assembly line

Q14. What is precursor‑directed biosynthesis in the context of secondary metabolite engineering?

• Gene deletion to block native pathways
• Feeding modified or non‑natural precursors to a producing organism to obtain analogs
• CRISPR‑based activation of silent gene clusters
• Chemical total synthesis of the natural product

Correct Answer: Feeding modified or non‑natural precursors to a producing organism to obtain analogs

Q15. What common effect does glycosylation have on secondary metabolites?

• Decreases molecular weight dramatically
• Increases solubility and can modify bioactivity and stability
• Always inactivates biological activity
• Removes stereocentres from the aglycone

Correct Answer: Increases solubility and can modify bioactivity and stability

Q16. Which five‑carbon building block is the fundamental unit for terpenoid biosynthesis?

• Acetyl‑CoA
• Malonyl‑CoA
• Isopentenyl pyrophosphate (IPP)
• Chorismate

Correct Answer: Isopentenyl pyrophosphate (IPP)

Q17. During polyketide chain elongation the decarboxylative condensation mechanism provides which key advantage?

• Generates ATP for the reaction
• Drives chain extension by releasing CO2 and providing thermodynamic favorability
• Introduces stereochemical inversion at every step
• Directly methylates the growing chain

Correct Answer: Drives chain extension by releasing CO2 and providing thermodynamic favorability

Q18. A typical secondary metabolite biosynthetic gene cluster often contains which combination of genes?

• Only structural enzyme genes without regulation
• Genes for biosynthetic enzymes, pathway‑specific regulators, transporters and resistance proteins
• Housekeeping metabolic genes unrelated to the product
• Only ribosomal protein genes

Correct Answer: Genes for biosynthetic enzymes, pathway‑specific regulators, transporters and resistance proteins

Q19. What is a frequent bottleneck encountered when expressing complex secondary metabolite pathways heterologously?

• Excessive natural product accumulation causing no toxicity
• Inadequate precursor supply and incompatible host metabolism
• Too many native gene clusters in the host leading to overproduction
• Instant folding and perfect activity of foreign enzymes

Correct Answer: Inadequate precursor supply and incompatible host metabolism

Q20. Which experimental approach is commonly used to trace the origin of atoms in a secondary metabolite and validate biosynthetic steps?

• Stable isotope labeling followed by LC‑MS and NMR analysis
• Only gene expression microarrays
• X‑ray crystallography of the whole producing strain
• Thin layer chromatography without labeling

Correct Answer: Stable isotope labeling followed by LC‑MS and NMR analysis

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