Understanding the formation of secondary metabolites is essential for B. Pharm students studying pharmacognosy, drug discovery, and natural product chemistry. This introduction covers biosynthetic pathways, key enzymes, and genetic regulation that drive production of alkaloids, terpenoids, and phenolics in plants, microbes, and fungi. Emphasis is placed on pathway intermediates, enzyme classes (like polyketide synthases and nonribosomal peptide synthetases), ecological roles, and pharmaceutical relevance such as lead identification and toxicity. Knowledge of extraction, analytical methods, and pathway manipulation supports rational drug development and biotechnological production. Strengthening these concepts builds a foundation for interpreting MCQs and practical applications in secondary metabolism. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which primary metabolic pathway provides aromatic precursors for many plant phenolic secondary metabolites?
- Mevalonate pathway
- Shikimate pathway
- Acetate-malonate (polyketide) pathway
- Methylerythritol phosphate (MEP) pathway
Correct Answer: Shikimate pathway
Q2. Which enzyme class is directly responsible for assembly of polyketide secondary metabolites?
- Terpene synthases
- Polyketide synthases (PKSs)
- Cytochrome P450 monooxygenases
- Glycosyltransferases
Correct Answer: Polyketide synthases (PKSs)
Q3. Nonribosomal peptide synthetases (NRPS) synthesize peptides independent of which cellular machinery?
- Ribosomes
- Spacer RNA
- DNA polymerases
- Chaperone proteins
Correct Answer: Ribosomes
Q4. Which pathway is the primary source of isoprenoid (terpenoid) backbones in plants via the cytosol?
- Methylerythritol phosphate (MEP) pathway
- Shikimate pathway
- Mevalonate (MVA) pathway
- Glycolysis
Correct Answer: Mevalonate (MVA) pathway
Q5. Which tailoring enzyme commonly introduces oxygen functionality into secondary metabolites, increasing polarity and reactivity?
- Polyketide synthase
- Cytochrome P450 monooxygenase
- Acyl carrier protein
- DNA methyltransferase
Correct Answer: Cytochrome P450 monooxygenase
Q6. Which secondary metabolite class typically contains nitrogen atoms derived from amino acids?
- Terpenoids
- Alkaloids
- Flavonoids
- Polyketides
Correct Answer: Alkaloids
Q7. In microbial secondary metabolism, genes responsible for a biosynthetic pathway are often organized as what?
- Operons for primary metabolism only
- Randomly scattered single genes
- Biosynthetic gene clusters
- Mitochondrial gene islands
Correct Answer: Biosynthetic gene clusters
Q8. Which analytical technique is most informative for determining molecular weight and fragmentation patterns of secondary metabolites?
- Nuclear magnetic resonance (NMR)
- Ultraviolet-visible spectrophotometry (UV-Vis)
- Mass spectrometry (MS)
- Infrared spectroscopy (IR)
Correct Answer: Mass spectrometry (MS)
Q9. Which pathway provides acetyl-CoA and malonyl-CoA building blocks for many polyketide natural products?
- Shikimate pathway
- Acetate-malonate pathway
- MEP pathway
- Urea cycle
Correct Answer: Acetate-malonate pathway
Q10. Elicitation in plant cell culture aims to increase secondary metabolite production by applying what?
- Antibiotics only
- Physical or chemical stressors and signaling molecules
- Excess nutrients to favor primary metabolism
- Low oxygen to inhibit biosynthesis
Correct Answer: Physical or chemical stressors and signaling molecules
Q11. Which method is commonly used to separate and quantify secondary metabolites in complex extracts?
- Thin-layer chromatography (TLC)
- Plate counting
- ELISA for proteins
- Gram staining
Correct Answer: Thin-layer chromatography (TLC)
Q12. Which biosynthetic precursor pair is central to terpenoid synthesis?
- Acetyl-CoA and malonyl-CoA
- Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP)
- Phenylalanine and tyrosine
- S-adenosylmethionine and folate
Correct Answer: Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP)
Q13. Glycosylation of secondary metabolites most commonly affects which property?
- Primary sequence of proteins
- Lipid bilayer composition
- Water solubility and bioavailability
- DNA replication fidelity
Correct Answer: Water solubility and bioavailability
Q14. Which of the following is a common regulatory mechanism that controls secondary metabolite gene clusters in microbes?
- Allosteric regulation of ribosomes
- Cluster-specific transcriptional activators or repressors
- Ubiquitin-mediated degradation
- Spliceosomal editing
Correct Answer: Cluster-specific transcriptional activators or repressors
Q15. The polyketide antibiotic erythromycin is biosynthesized by which type of PKS?
- Type III PKS (chalcone synthase-like)
- Type II PKS (iterative aromatic)
- Type I modular PKS
- Nonribosomal PKS hybrid
Correct Answer: Type I modular PKS
Q16. Which natural product class is typically synthesized from the shikimate pathway followed by enzymatic modifications?
- Alkaloids derived from terpenes
- Phenolic compounds and many flavonoids
- Polyketide macrolides
- Steroids
Correct Answer: Phenolic compounds and many flavonoids
Q17. Which technique gives detailed structural information including stereochemistry for isolated secondary metabolites?
- Gas chromatography with flame ionization detector (GC-FID)
- Nuclear magnetic resonance (NMR) spectroscopy
- Paper chromatography
- Simple UV screening
Correct Answer: Nuclear magnetic resonance (NMR) spectroscopy
Q18. Methylation of secondary metabolites is typically catalyzed by enzymes using which methyl donor?
- ATP
- S-adenosylmethionine (SAM)
- Acetyl-CoA
- NADPH
Correct Answer: S-adenosylmethionine (SAM)
Q19. Which ecological function is commonly attributed to plant secondary metabolites?
- Catalyzing glycolysis
- Defense against herbivores and pathogens
- Maintaining turgor pressure
- Protein synthesis
Correct Answer: Defense against herbivores and pathogens
Q20. Many antibiotics from actinomycetes are produced maximally during which growth phase?
- Exponential (log) phase
- Stationary phase
- Lag phase
- Death phase
Correct Answer: Stationary phase
Q21. Which factor commonly downregulates secondary metabolite production in fermentation if provided in excess?
- Nutrient limitation
- High concentration of preferred carbon source (catabolite repression)
- Low temperature
- Presence of elicitors
Correct Answer: High concentration of preferred carbon source (catabolite repression)
Q22. A glycoside secondary metabolite contains what bonded group?
- A sulfate ester attached to a protein
- A sugar moiety bound to an aglycone
- An amino acid linked to fatty acid
- A phosphate attached to a lipid
Correct Answer: A sugar moiety bound to an aglycone
Q23. Biotransformation in microbes is useful in drug development because it can:
- Eliminate all chiral centers
- Generate new derivatives and modify functional groups selectively
- Increase primary metabolism exclusively
- Destroy active pharmacophores
Correct Answer: Generate new derivatives and modify functional groups selectively
Q24. Which of the following is a common analytical hyphenated technique for separating and identifying secondary metabolites?
- HPLC-MS (High performance liquid chromatography–mass spectrometry)
- Simple distillation
- Paper electrophoresis
- Gram staining
Correct Answer: HPLC-MS (High performance liquid chromatography–mass spectrometry)
Q25. Which statement best describes “silent” or cryptic biosynthetic gene clusters?
- They encode essential primary metabolic enzymes only
- They are inactive under standard laboratory conditions but can produce metabolites when activated
- They are always expressed at high levels
- They only occur in plants
Correct Answer: They are inactive under standard laboratory conditions but can produce metabolites when activated
Q26. Which cofactor is most commonly required by hydroxylase enzymes involved in secondary metabolism?
- FAD or NADPH for monooxygenases
- ATP exclusively
- Biotin only
- Thiamine pyrophosphate only
Correct Answer: FAD or NADPH for monooxygenases
Q27. Which compound class is typically derived from the mevalonate and MEP pathways and includes many essential oil constituents?
- Alkaloids
- Terpenoids
- Flavonoids
- Polyketides
Correct Answer: Terpenoids
Q28. Radioisotope labeling studies are useful in secondary metabolism mainly to:
- Measure toxicity of compounds
- Track incorporation of precursors into product molecules and elucidate pathways
- Sterilize culture media
- Create nonradioactive analogs
Correct Answer: Track incorporation of precursors into product molecules and elucidate pathways
Q29. Which drug discovery strategy leverages knowledge of secondary metabolite biosynthesis to create novel compounds?
- Genome mining and combinatorial biosynthesis
- Randomized clinical trials
- Only chemical synthesis without biosynthetic insight
- Ignoring gene cluster information
Correct Answer: Genome mining and combinatorial biosynthesis
Q30. Which extraction solvent property is most important when isolating polar glycosylated secondary metabolites?
- Nonpolar solvent like hexane
- Polar solvent such as methanol or water
- Inert gas atmosphere
- Strongly acidic chloroform
Correct Answer: Polar solvent such as methanol or water
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com