Composition and chemistry of secondary metabolites MCQs With Answer is a focused resource for B. Pharm students studying phytochemistry, pharmacognosy and natural-product drug discovery. This concise introduction and question set highlights composition, major classes (alkaloids, terpenoids, phenolics, glycosides, saponins, steroids), biosynthetic pathways (shikimate, mevalonate, MEP/DOXP), structure–activity relationships, chemotaxonomy, analytical techniques and pharmacological relevance. Emphasis is on identification tests, isolation methods, metabolic engineering and clinical implications of secondary metabolites. These MCQs are designed to deepen conceptual understanding and improve exam readiness by linking chemical composition to biological activity and therapeutic potential. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which biosynthetic pathway primarily provides precursors for aromatic secondary metabolites such as phenolics and flavonoids?
- Mevalonate pathway
- Shikimate pathway
- Fatty acid synthesis
- Polyketide pathway
Correct Answer: Shikimate pathway
Q2. Which class of secondary metabolites is characterized by nitrogen-containing heterocycles and often pronounced pharmacological activity?
- Terpenoids
- Alkaloids
- Phenolics
- Saponins
Correct Answer: Alkaloids
Q3. The MEP/DOXP pathway is an alternative to the mevalonate pathway and operates in which cellular compartment of plants?
- Cytosol
- Endoplasmic reticulum
- Chloroplasts
- Mitochondria
Correct Answer: Chloroplasts
Q4. Which analytical technique is most commonly used for separating and identifying complex mixtures of plant secondary metabolites?
- FTIR spectroscopy
- High-performance liquid chromatography (HPLC)
- Ultracentrifugation
- Flame photometry
Correct Answer: High-performance liquid chromatography (HPLC)
Q5. Cardiac glycosides like digoxin are classified under which chemical group of secondary metabolites?
- Alkaloids
- Steroid glycosides
- Flavonoids
- Terpenoids
Correct Answer: Steroid glycosides
Q6. Which colorimetric test is classically used to detect phenolic hydroxyl groups in plant extracts?
- Dragendorff’s reagent
- Ferric chloride test
- Liebermann–Burchard test
- Kedde test
Correct Answer: Ferric chloride test
Q7. Which enzyme class catalyzes the cyclization steps in terpenoid biosynthesis?
- Glycosyltransferases
- Terpene synthases (cyclases)
- Proteases
- Dehydrogenases only
Correct Answer: Terpene synthases (cyclases)
Q8. Flavonoids are biosynthesized mainly from which two basic building blocks?
- Acetyl-CoA and malonyl-CoA
- Isopentenyl pyrophosphate and dimethylallyl pyrophosphate
- P-coumaroyl-CoA and malonyl-CoA
- Shikimic acid and chorismic acid
Correct Answer: P-coumaroyl-CoA and malonyl-CoA
Q9. Saponins possess surfactant properties due to the presence of which structural features?
- Peptide chains
- Sugar moieties attached to a lipophilic aglycone
- Multiple aromatic rings
- Phosphate esters
Correct Answer: Sugar moieties attached to a lipophilic aglycone
Q10. Which secondary metabolite class commonly contributes to plant pigmentation and antioxidant activity?
- Alkaloids
- Terpenes
- Flavonoids
- Polyamines
Correct Answer: Flavonoids
Q11. Which of the following is a typical biosynthetic origin for terpenoids?
- Polyketide pathway
- Mevalonate and MEP pathways from isoprene units
- Shikimate pathway
- Nonribosomal peptide synthesis
Correct Answer: Mevalonate and MEP pathways from isoprene units
Q12. Which chromatographic detector is particularly useful for detecting nitrogen-containing secondary metabolites like alkaloids?
- Refractive index detector
- UV–visible detector with appropriate wavelength
- Electrochemical detector
- Flame ionization detector
Correct Answer: UV–visible detector with appropriate wavelength
Q13. What is chemotaxonomy in the context of secondary metabolites?
- Classification based on genetic sequences only
- Use of chemical profiles of secondary metabolites to classify and differentiate organisms
- Taxonomic classification using morphological characters
- Using soil chemistry to classify plants
Correct Answer: Use of chemical profiles of secondary metabolites to classify and differentiate organisms
Q14. Which structural change often increases water solubility of an otherwise lipophilic secondary metabolite?
- Methylation of hydroxyl groups
- Glycosylation (attachment of sugar)
- Hydrogenation of double bonds
- Removal of hydroxyl groups
Correct Answer: Glycosylation (attachment of sugar)
Q15. Which reagent is used specifically to detect steroidal or triterpenoid compounds (color test)?
- Dragendorff’s reagent
- Liebermann–Burchard reagent
- Ninhydrin reagent
- Biuret reagent
Correct Answer: Liebermann–Burchard reagent
Q16. Alkaloids are typically biosynthesized from which type of primary metabolites?
- Amino acids
- Fatty acids
- Simple sugars
- Nucleotides
Correct Answer: Amino acids
Q17. Which secondary metabolite group is commonly associated with bitter taste and has membrane-disrupting activity against microbes?
- Saponins
- Flavonoids
- Alkaloids
- Terpenoids
Correct Answer: Saponins
Q18. In metabolic engineering to increase production of a plant secondary metabolite, which strategy is commonly used?
- Knockout of biosynthetic pathway genes
- Overexpression of rate-limiting enzymes in the pathway
- Removal of precursor supply
- Inhibition of transporter proteins only
Correct Answer: Overexpression of rate-limiting enzymes in the pathway
Q19. Which secondary metabolite class often acts as phytoalexins—compounds produced in response to pathogen attack?
- Phenolics and flavonoids
- Carbohydrates
- Proteins
- Vitamins
Correct Answer: Phenolics and flavonoids
Q20. Which technique provides structural information such as molecular weight and fragmentation patterns for secondary metabolites?
- Thin-layer chromatography (TLC)
- Mass spectrometry (MS)
- Paper chromatography
- Microscopy
Correct Answer: Mass spectrometry (MS)
Q21. Which secondary metabolite type commonly includes molecules like paclitaxel and artemisinin with anticancer or antimalarial activity?
- Alkaloids only
- Terpenoids and diterpenes
- Carotenoids
- Tannins
Correct Answer: Terpenoids and diterpenes
Q22. Tannins are high-molecular-weight phenolics known for which pharmacological property?
- Protein precipitation and astringent activity
- Strong basicity
- Enzymatic activity
- Cell membrane formation
Correct Answer: Protein precipitation and astringent activity
Q23. Nonribosomal peptide secondary metabolites are synthesized by which type of enzymatic complex?
- Polyketide synthases
- Nonribosomal peptide synthetases (NRPS)
- Ribosomes
- Glycosyltransferases
Correct Answer: Nonribosomal peptide synthetases (NRPS)
Q24. Which functional group is commonly involved in radical scavenging activity of phenolic antioxidants?
- Carbonyl groups
- Hydroxyl groups attached to aromatic rings
- Ether linkages
- Alkyl chains
Correct Answer: Hydroxyl groups attached to aromatic rings
Q25. Which property of secondary metabolites is most important when considering oral bioavailability of a plant-derived drug?
- Color of the compound
- Lipophilicity and molecular size
- Melting point only
- Ability to bind cellulose
Correct Answer: Lipophilicity and molecular size
Q26. Which isolation technique is appropriate for volatile terpenes from plant material?
- Steam distillation or hydrodistillation
- Ion-exchange chromatography
- Gel electrophoresis
- Vacuum drying only
Correct Answer: Steam distillation or hydrodistillation
Q27. Which term describes small non-protein secondary metabolites that mediate plant–microbe or plant–plant communication?
- Primary metabolites
- Allelochemicals
- Structural polysaccharides
- Dietary fibers
Correct Answer: Allelochemicals
Q28. Which chemical modification often reduces toxicity and facilitates excretion of xenobiotic secondary metabolites in mammals?
- Methylation to increase lipophilicity
- Conjugation with glucuronic acid or sulfate
- Removing polar groups
- Cross-linking with proteins
Correct Answer: Conjugation with glucuronic acid or sulfate
Q29. Structure–activity relationship (SAR) studies of alkaloids typically explore which aspect?
- How different substituents affect pharmacological potency and selectivity
- Soil composition where plant grows
- Only the natural abundance of alkaloids
- Color changes on exposure to light
Correct Answer: How different substituents affect pharmacological potency and selectivity
Q30. Which regulatory consideration is critical when developing a secondary-metabolite-based drug from plant extracts?
- Documented safety, standardization of active constituents and reproducible quality control
- Only folklore use is sufficient
- Ignoring batch-to-batch variation
- Disregarding toxicology studies
Correct Answer: Documented safety, standardization of active constituents and reproducible quality control
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