Biosources of secondary metabolites examine natural origins—plants, microbes, fungi and marine organisms—that synthesize diverse bioactive compounds crucial to pharmaceutical research. For B. Pharm students, this concise overview links biosynthetic pathways (shikimate, mevalonate, polyketide), major classes (alkaloids, terpenoids, phenolics, glycosides), ecological roles and practical isolation and characterization techniques. Emphasis is placed on analytical approaches (TLC, HPLC, GC-MS, NMR), extraction and purification, structure–activity relationships, and applications in drug discovery, quality control and pharmacognosy. Understanding genetic regulation, microbial and endophytic sources, and biotransformation expands capability in natural product research. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which biosynthetic pathway is primarily responsible for the formation of aromatic amino acid–derived secondary metabolites?
- The mevalonate pathway
- The shikimate pathway
- The non-mevalonate (MEP) pathway
- The polyketide pathway
Correct Answer: The shikimate pathway
Q2. Which class of secondary metabolites is biosynthesized mainly from isoprene (C5) units?
- Alkaloids
- Phenolics
- Terpenoids
- Glycosides
Correct Answer: Terpenoids
Q3. A common microbial source of clinically important secondary metabolites like erythromycin is:
- Bacillus subtilis
- Escherichia coli
- Streptomyces species
- Saccharomyces cerevisiae
Correct Answer: Streptomyces species
Q4. Which precursor is central to polyketide biosynthesis?
- Amino acids
- Acetyl-CoA and malonyl-CoA
- Isopentenyl pyrophosphate (IPP)
- Shikimic acid
Correct Answer: Acetyl-CoA and malonyl-CoA
Q5. Which analytical technique gives direct information about molecular weight and fragmentation patterns of secondary metabolites?
- Thin layer chromatography (TLC)
- High-performance liquid chromatography (HPLC)
- Gas chromatography–mass spectrometry (GC-MS)
- Ultraviolet-visible spectrophotometry (UV-Vis)
Correct Answer: Gas chromatography–mass spectrometry (GC-MS)
Q6. Which reagent is commonly used as a qualitative test for alkaloids?
- Ferric chloride
- Dragendorff’s reagent
- Molisch’s reagent
- Shinoda reagent
Correct Answer: Dragendorff’s reagent
Q7. Endophytic microorganisms are important because they:
- Always decrease secondary metabolite yield in host plants
- Can produce bioactive secondary metabolites similar to their host
- Are only plant pathogens and not useful for drug discovery
- Are synthetic sources of terpenoids
Correct Answer: Can produce bioactive secondary metabolites similar to their host
Q8. Which class of secondary metabolites includes flavonoids and phenolic acids?
- Alkaloids
- Phenolics
- Saponins
- Terpenes
Correct Answer: Phenolics
Q9. The mevalonate pathway operates in which cellular compartment of plants for terpenoid biosynthesis?
- Plastids
- Mitochondria
- Cytosol
- Golgi apparatus
Correct Answer: Cytosol
Q10. Which technique is most suitable for separating non-volatile polar plant secondary metabolites prior to detection?
- Gas chromatography (GC)
- Thin layer chromatography (TLC)
- High-performance liquid chromatography (HPLC)
- Paper chromatography only
Correct Answer: High-performance liquid chromatography (HPLC)
Q11. Which enzyme type is central to terpene skeleton formation by catalyzing cyclization of prenyl diphosphates?
- Polyketide synthases (PKS)
- Terpene synthases (TPS)
- Oxidoreductases
- Glycosyltransferases
Correct Answer: Terpene synthases (TPS)
Q12. Which of the following is a typical ecological role of secondary metabolites in plants?
- Serve as primary energy currency
- Assist in photosynthetic electron transport
- Defense against herbivores and pathogens
- Form structural components of cell walls exclusively
Correct Answer: Defense against herbivores and pathogens
Q13. Biotransformation in microbial cultures is useful in drug development because it:
- Always destroys the parent compound
- Generates human-identical metabolites for safety studies
- Is only a contamination concern and not purposeful
- Prevents isolation of secondary metabolites
Correct Answer: Generates human-identical metabolites for safety studies
Q14. Which secondary metabolite class typically contains nitrogen atoms?
- Terpenoids
- Polyketides
- Alkaloids
- Flavonoids
Correct Answer: Alkaloids
Q15. Which parameter most directly influences secondary metabolite production in plant cell cultures?
- Light intensity only
- Medium composition and elicitors
- Container shape only
- Presence of soil microbes exclusively
Correct Answer: Medium composition and elicitors
Q16. Which spectroscopic method provides detailed information about molecular structure, including carbon-hydrogen framework?
- Infrared spectroscopy (IR)
- Nuclear magnetic resonance (NMR)
- UV-Visible spectroscopy
- Thin layer chromatography (TLC)
Correct Answer: Nuclear magnetic resonance (NMR)
Q17. Glycosides are secondary metabolites characterized by:
- A sugar moiety linked to an aglycone
- Only amino acid residues
- A volatile terpenoid core without sugars
- Being exclusively synthesized by bacteria
Correct Answer: A sugar moiety linked to an aglycone
Q18. The term “secondary metabolite gene cluster” refers to:
- Random scattered genes unrelated to metabolite biosynthesis
- A genomic region containing co-located biosynthetic genes for a pathway
- Only ribosomal protein genes
- Genes involved in primary metabolism only
Correct Answer: A genomic region containing co-located biosynthetic genes for a pathway
Q19. Which method is commonly used for preliminary profiling of plant extracts for multiple classes of metabolites?
- Bioassay-guided isolation without chromatography
- Thin layer chromatography (TLC) with multiple detection reagents
- Single-wavelength UV measurement only
- Light microscopy
Correct Answer: Thin layer chromatography (TLC) with multiple detection reagents
Q20. Which marine organism type is a rich and unique source of novel secondary metabolites?
- Terrestrial grasses
- Coral reef sponges and associated microbes
- Freshwater algae only
- Wood-decay fungi exclusively
Correct Answer: Coral reef sponges and associated microbes
Q21. Which secondary metabolite class is commonly assayed using the Liebermann–Burchard reaction?
- Alkaloids
- Steroids and triterpenoids
- Flavonoids
- Polyketides
Correct Answer: Steroids and triterpenoids
Q22. Horizontal gene transfer in microbes can influence secondary metabolite diversity by:
- Limiting biosynthetic capability only within one species
- Spreading biosynthetic gene clusters between species
- Removing all secondary metabolite genes
- Preventing expression of polyketide synthases
Correct Answer: Spreading biosynthetic gene clusters between species
Q23. Which statement about primary vs secondary metabolites is correct?
- Primary metabolites are non-essential for growth and development
- Secondary metabolites are directly involved in basic cellular processes
- Secondary metabolites often have ecological functions and specialized bioactivities
- Primary metabolites are always toxic to other organisms
Correct Answer: Secondary metabolites often have ecological functions and specialized bioactivities
Q24. Which plant tissue is often richest in certain secondary metabolites such as alkaloids?
- Xylem only
- Young leaves and specialized glands or trichomes
- Dead bark exclusively
- Root xylem vessels only
Correct Answer: Young leaves and specialized glands or trichomes
Q25. In quality control of herbal products, marker compounds are used to:
- Obscure the real chemical composition
- Standardize and ensure batch-to-batch consistency
- Eliminate need for any extraction methods
- Guarantee absence of all contaminants
Correct Answer: Standardize and ensure batch-to-batch consistency
Q26. Which enzymatic complex is analogous to fatty acid synthase and builds many polyketide structures?
- Terpene cyclase complex
- Polyketide synthase (PKS)
- Ribosome
- Phenylalanine ammonia-lyase (PAL)
Correct Answer: Polyketide synthase (PKS)
Q27. Which factor is least likely to affect secondary metabolite profile in plants?
- Seasonal variation
- Soil nutrients and stress
- Plant developmental stage
- Color of laboratory walls
Correct Answer: Color of laboratory walls
Q28. Flavonoids are biosynthesized mainly via which combined pathway?
- Mevalonate and MEP pathways
- Shikimate and acetate (polyketide) pathways
- Only glycolysis
- Non-ribosomal peptide synthetase pathway
Correct Answer: Shikimate and acetate (polyketide) pathways
Q29. Which approach is most appropriate for discovering new secondary metabolites from uncultivable microbes?
- Traditional agar culture only
- Metagenomic screening of environmental DNA
- Discarding environmental samples as useless
- Using only light microscopy
Correct Answer: Metagenomic screening of environmental DNA
Q30. Which concept best describes selecting extracts by biological activity and then isolating active compounds?
- Chemical fingerprinting
- Bioassay-guided fractionation
- Random screening without assays
- Complete genome sequencing
Correct Answer: Bioassay-guided fractionation
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.
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