Definition of secondary metabolites MCQs With Answer — This concise introduction defines secondary metabolites, their biosynthetic origins, chemical classes and pharmacological relevance for B.Pharm students. Secondary metabolites are non-essential but bioactive compounds produced by plants, microbes and fungi via pathways such as shikimate, mevalonate and polyketide routes. Key classes include alkaloids, terpenoids and phenolics with roles in defense, signaling and drug lead discovery. Understanding structure–activity relationships, biosynthetic gene clusters, analytical techniques (TLC, HPLC, GC‑MS) and strategies to enhance production (elicitation, cell culture, metabolic engineering) is essential for pharmaceutics. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which statement best defines secondary metabolites?
- Compounds essential for basic cellular metabolism and growth
- Non-essential bioactive compounds produced by organisms for ecological interactions
- Inorganic ions needed for enzyme cofactors
- Primary energy storage molecules like ATP
Correct Answer: Non-essential bioactive compounds produced by organisms for ecological interactions
Q2. Which biosynthetic pathway is primarily responsible for the formation of aromatic amino acid‑derived secondary metabolites?
- Mevalonate pathway
- Shikimate pathway
- Polyketide synthase pathway
- Methylerythritol phosphate (MEP) pathway
Correct Answer: Shikimate pathway
Q3. Which class of secondary metabolites is produced via isoprenoid pathways (mevalonate/MEP)?
- Alkaloids
- Terpenoids
- Flavonoids
- Polyketides
Correct Answer: Terpenoids
Q4. Penicillin is an example of which type of secondary metabolite?
- Terpenoid
- Alkaloid
- β‑lactam antibiotic derived from fungal secondary metabolism
- Phenolic tannin
Correct Answer: β‑lactam antibiotic derived from fungal secondary metabolism
Q5. Which enzyme systems are central to polyketide natural product biosynthesis?
- Non‑ribosomal peptide synthetases (NRPS)
- Polyketide synthases (PKS)
- Terpene cyclases
- Cytochrome P450 reductases only
Correct Answer: Polyketide synthases (PKS)
Q6. Which analytical technique is most suitable for separating closely related non‑volatile plant secondary metabolites?
- Gas chromatography (GC)
- High‑performance liquid chromatography (HPLC)
- Atomic absorption spectroscopy
- Gel electrophoresis
Correct Answer: High‑performance liquid chromatography (HPLC)
Q7. Which secondary metabolite class typically contains nitrogen in their structures?
- Terpenoids
- Alkaloids
- Phenolics
- Polyketides without nitrogen
Correct Answer: Alkaloids
Q8. The precursor molecule for most monoterpenes (C10) is which isoprenoid unit?
- Isopentenyl pyrophosphate (IPP) dimer forming geranyl pyrophosphate (GPP)
- Farnesyl pyrophosphate (FPP)
- Geranylgeranyl pyrophosphate (GGPP)
- Acetyl‑CoA directly
Correct Answer: Isopentenyl pyrophosphate (IPP) dimer forming geranyl pyrophosphate (GPP)
Q9. Flavonoids are classified under which broader chemical group?
- Lipids
- Phenolic compounds
- Alkaloids
- Sugars
Correct Answer: Phenolic compounds
Q10. Which role is NOT commonly attributed to secondary metabolites in plants?
- Defense against herbivores and pathogens
- Attraction of pollinators
- Primary ATP production for respiration
- Allelopathic interactions with competing plants
Correct Answer: Primary ATP production for respiration
Q11. Which technique is widely used to identify volatile secondary metabolites?
- Liquid chromatography‑mass spectrometry (LC‑MS)
- Gas chromatography‑mass spectrometry (GC‑MS)
- Northern blotting
- X‑ray crystallography
Correct Answer: Gas chromatography‑mass spectrometry (GC‑MS)
Q12. Which of the following is a classic alkaloid used as an analgesic derived from opium poppy?
- Quinine
- Morphine
- Penicillin
- Atropine
Correct Answer: Morphine
Q13. Which concept explains clusters of genes encoding an entire secondary metabolite pathway in microbes?
- Operon‑like biosynthetic gene clusters
- Random single‑gene distribution
- Only post‑translational regulation
- Chromosomal telomeres
Correct Answer: Operon‑like biosynthetic gene clusters
Q14. Elicitation in plant cell culture aims to:
- Suppress secondary metabolite production
- Enhance secondary metabolite synthesis using biotic or abiotic stimuli
- Convert secondary metabolites to primary metabolites
- Increase DNA replication rate
Correct Answer: Enhance secondary metabolite synthesis using biotic or abiotic stimuli
Q15. Which modification commonly increases water solubility of plant secondary metabolites?
- Methylation only
- Glycosylation
- Dehydration
- Polymerization into lignin
Correct Answer: Glycosylation
Q16. Statins, used as cholesterol‑lowering drugs, are derived from which class of microbial secondary metabolites?
- Alkaloids from plants
- Polyketide or polyketide‑like fungal metabolites
- Monoterpenes
- Synthetic peptides only, not natural
Correct Answer: Polyketide or polyketide‑like fungal metabolites
Q17. Non‑ribosomal peptide synthetases (NRPS) synthesize secondary metabolites that are typically:
- Ribosomally encoded peptides
- Peptide‑like molecules assembled independently of the ribosome
- Carbohydrates
- Lipids derived from fatty acid synthase only
Correct Answer: Peptide‑like molecules assembled independently of the ribosome
Q18. Which factor commonly leads to activation of silent biosynthetic gene clusters in microbes?
- Standard rich media without stress
- Co‑culture with competing microorganisms or specific elicitors
- Deletion of ribosomal RNA genes
- Freezing cultures at −80°C
Correct Answer: Co‑culture with competing microorganisms or specific elicitors
Q19. Quinine, used to treat malaria, is classified as which type of compound?
- Terpenoid
- Alkaloid from Cinchona species
- Phenolic antioxidant
- Saponin glycoside
Correct Answer: Alkaloid from Cinchona species
Q20. Which cellular compartment in plants is commonly associated with storage of some secondary metabolites?
- Mitochondrial matrix exclusively
- Vacuoles and specialized glandular trichomes
- Nucleus
- Peroxisomes only
Correct Answer: Vacuoles and specialized glandular trichomes
Q21. Which reagent is commonly used for preliminary detection of phenolic compounds on a TLC plate?
- Dragendorff’s reagent
- Ferric chloride solution (FeCl3)
- Ninhydrin reagent
- Salkowski reagent for terpenes
Correct Answer: Ferric chloride solution (FeCl3)
Q22. Which property often correlates with the pharmacological activity of an alkaloid?
- Presence of aromatic hydroxyl groups only
- Basic nitrogen that can interact with biological receptors
- High carbohydrate content
- Lack of heteroatoms
Correct Answer: Basic nitrogen that can interact with biological receptors
Q23. Which strategy is used in metabolic engineering to increase production of a desired secondary metabolite?
- Downregulate all pathway enzymes
- Overexpress rate‑limiting enzymes and supply precursor pools
- Eliminate transporter proteins to trap substrates outside cells
- Remove promoter regions for biosynthetic genes
Correct Answer: Overexpress rate‑limiting enzymes and supply precursor pools
Q24. Tannins and lignins are polymeric examples of which major chemical family?
- Alkaloids
- Phenolic compounds derived from phenylpropanoid metabolism
- Terpenes
- Steroids only
Correct Answer: Phenolic compounds derived from phenylpropanoid metabolism
Q25. Which secondary metabolite class commonly serves as insect feeding deterrents in plants?
- Primary amino acids
- Saponins and alkaloids
- Chlorophyll molecules
- Ribosomal proteins
Correct Answer: Saponins and alkaloids
Q26. Which of the following best describes a non‑proteinogenic amino acid commonly found in some secondary metabolites?
- Lysine used in proteins only
- Unusual amino acids incorporated by NRPS into peptides
- Standard ribosomal glycine exclusively
- Only phosphorylated serine residues
Correct Answer: Unusual amino acids incorporated by NRPS into peptides
Q27. Which plant secondary metabolite was historically important as an antimalarial and is still used in derivatives today?
- Atropine
- Artemisinin from Artemisia annua
- Morphine
- Taxol only for cancer
Correct Answer: Artemisinin from Artemisia annua
Q28. Which characteristic distinguishes secondary from primary metabolites?
- Secondary metabolites are universally required for cell survival in culture
- Primary metabolites are involved in growth and central metabolism; secondary are specialized and ecological
- Secondary metabolites are always proteins
- Primary metabolites are only produced at night
Correct Answer: Primary metabolites are involved in growth and central metabolism; secondary are specialized and ecological
Q29. Which analytical approach allows structural elucidation (detailed structure) of an isolated secondary metabolite?
- Thin layer chromatography alone
- Nuclear magnetic resonance (NMR) spectroscopy often combined with MS
- Simple refractometry
- Paper chromatography without detectors
Correct Answer: Nuclear magnetic resonance (NMR) spectroscopy often combined with MS
Q30. Which pharmaceutical example demonstrates that plant secondary metabolites can be anticancer agents?
- Penicillin as an anticancer antibiotic
- Paclitaxel (Taxol) derived from Taxus species used in chemotherapy
- Aspirin derived solely from microbes
- Insulin derived from willow bark
Correct Answer: Paclitaxel (Taxol) derived from Taxus species used in chemotherapy
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