This collection of Ultra-structure of bacteria MCQs With Answer is crafted for B. Pharm students to strengthen understanding of bacterial cell architecture and its pharmacological implications. The questions focus on bacterial ultrastructure topics such as peptidoglycan chemistry, Gram-positive and Gram-negative envelopes, lipopolysaccharide, cytoplasmic membrane transport, 70S ribosomes, plasmids, flagella, pili, capsules, endospores, inclusion bodies and prokaryotic cytoskeleton proteins. Emphasis on mechanisms of antibiotic action (β-lactams, aminoglycosides, macrolides), staining techniques, secretion systems and resistance bridges microbiology to drug therapy. Each question has clear options and correct answers for quick revision.
‘Now let’s test your knowledge with 50 MCQs on this topic.’
Q1. Which polymer is the main structural component of the bacterial cell wall?
- Peptidoglycan
- Cellulose
- Chitin
- Glycosaminoglycan
Correct Answer: Peptidoglycan
Q2. The peptide sequence involved in cross-linking peptidoglycan commonly terminates in which dipeptide?
- L-Ala-L-Ala
- D-Ala-D-Ala
- D-Ser-D-Lys
- L-Lys-L-Ala
Correct Answer: D-Ala-D-Ala
Q3. Which feature is characteristic of Gram-positive bacterial cell envelopes?
- Presence of teichoic acids in a thick peptidoglycan layer
- Presence of an outer membrane with lipopolysaccharide
- A very thin peptidoglycan layer and periplasmic space
- Predominant mycolic acid-rich cell wall
Correct Answer: Presence of teichoic acids in a thick peptidoglycan layer
Q4. The outer membrane of Gram-negative bacteria contains which major endotoxin component?
- Lipoteichoic acid
- Lipopolysaccharide (LPS)
- Mycolic acid
- Teichoic acid
Correct Answer: Lipopolysaccharide (LPS)
Q5. What is the periplasmic space in Gram-negative bacteria?
- The cytoplasmic matrix where DNA is located
- The space between outer membrane and cytoplasmic membrane containing enzymes
- The capsule external to the cell wall
- The space inside the cytoplasmic membrane
Correct Answer: The space between outer membrane and cytoplasmic membrane containing enzymes
Q6. What is the sedimentation coefficient and subunit composition of bacterial ribosomes?
- 80S composed of 60S and 40S
- 70S composed of 50S and 30S
- 70S composed of 60S and 10S
- 90S composed of 60S and 30S
Correct Answer: 70S composed of 50S and 30S
Q7. Which antibiotic class primarily targets the 30S ribosomal subunit?
- Macrolides
- Aminoglycosides
- β-lactams
- Fluoroquinolones
Correct Answer: Aminoglycosides
Q8. β-lactam antibiotics inhibit bacterial growth by binding to which target?
- DNA gyrase
- Transpeptidase enzymes (penicillin-binding proteins)
- RNA polymerase
- Aminoacyl-tRNA synthetase
Correct Answer: Transpeptidase enzymes (penicillin-binding proteins)
Q9. Lysozyme hydrolyzes which bond in peptidoglycan?
- Peptide bond between L-Lys and D-Ala
- β-(1,4) glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine
- Phosphodiester bond of lipopolysaccharide
- α-(1,6) glycosidic bond of teichoic acids
Correct Answer: β-(1,4) glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine
Q10. What confers extreme heat and chemical resistance to bacterial endospores?
- High content of teichoic acids and peptidoglycan
- Dipicolinic acid complexed with calcium and small acid‑soluble proteins (SASPs)
- Mycolic acids densely packed in the cortex
- Outer membrane rich in lipopolysaccharide
Correct Answer: Dipicolinic acid complexed with calcium and small acid‑soluble proteins (SASPs)
Q11. Bacterial capsules are primarily composed of which material in most species?
- Polysaccharides
- Peptidoglycan
- Lipid A
- Teichoic acid
Correct Answer: Polysaccharides
Q12. The primary role of fimbriae (pili) in pathogenic bacteria is:
- ATP generation
- Attachment to host cells and surfaces
- Protein synthesis
- Spore formation
Correct Answer: Attachment to host cells and surfaces
Q13. The filament of a bacterial flagellum is polymerized from which protein?
- Tubulin
- Actin
- Flagellin
- Pilin
Correct Answer: Flagellin
Q14. What powers rotation of the bacterial flagellar motor in most species?
- ATP hydrolysis at the basal body
- Proton motive force across the cytoplasmic membrane
- Direct sunlight absorption
- Membrane-bound chlorophyll activity
Correct Answer: Proton motive force across the cytoplasmic membrane
Q15. In the Gram stain procedure, the role of iodine (mordant) is to:
- Form a complex with crystal violet to trap the dye in peptidoglycan
- Decolorize Gram-negative cells
- Act as the primary stain
- Serve as the counterstain
Correct Answer: Form a complex with crystal violet to trap the dye in peptidoglycan
Q16. Acid-fast bacteria such as Mycobacterium have cell walls rich in which component?
- Teichoic acids
- Mycolic acids
- Lipopolysaccharide
- Cellulose
Correct Answer: Mycolic acids
Q17. Which protein export pathway transports folded proteins across the cytoplasmic membrane?
- Sec pathway (transports unfolded proteins)
- Tat pathway (transports folded proteins)
- Type III secretion (injects effectors)
- Type I secretion (ABC transport)
Correct Answer: Tat pathway (transports folded proteins)
Q18. Magnetosomes in some bacteria contain crystals of which material that orient cells in magnetic fields?
- Calcium carbonate
- Magnetite (Fe3O4)
- Elemental sulfur
- Polyhydroxybutyrate
Correct Answer: Magnetite (Fe3O4)
Q19. Plasmids are best described as:
- Membrane-bound organelles that perform photosynthesis
- Chromosomal fragments integrated into the nucleoid
- Extrachromosomal DNA molecules that often carry antibiotic resistance genes
- Polysaccharide inclusions for carbon storage
Correct Answer: Extrachromosomal DNA molecules that often carry antibiotic resistance genes
Q20. Which genetic element can move from one position to another within the genome?
- Ribosomal RNA genes
- Transposons (insertion sequences)
- Glycogen granules
- Capsular polysaccharides
Correct Answer: Transposons (insertion sequences)
Q21. Which bacterial cytoskeletal protein is homologous to tubulin and is essential for cell division?
- MreB
- FtsZ
- ParM
- Crescentin (CreS)
Correct Answer: FtsZ
Q22. Which protein is primarily responsible for maintaining rod shape in many bacteria?
- FtsZ
- MreB
- ParM
- Flagellin
Correct Answer: MreB
Q23. Which enzymatic activity polymerizes the glycan strands of peptidoglycan?
- Transpeptidase
- Transglycosylase
- DNA polymerase
- Peptidase
Correct Answer: Transglycosylase
Q24. Which part of lipopolysaccharide is primarily responsible for endotoxic shock?
- O-antigen
- Lipid A
- Core polysaccharide
- Peptidoglycan
Correct Answer: Lipid A
Q25. Which staining technique is commonly used to visualize bacterial capsules?
- Gram stain
- India ink (negative stain)
- Ziehl-Neelsen acid-fast stain
- Endospore stain
Correct Answer: India ink (negative stain)
Q26. Polyhydroxybutyrate (PHB) granules in bacteria are primarily storage sites for:
- Sulfur
- Phosphate
- Carbon as polyhydroxyalkanoates
- Iron
Correct Answer: Carbon as polyhydroxyalkanoates
Q27. Where is the bacterial chromosome typically located within the cell?
- Inside membrane-bound nucleus
- Within the nucleoid region of the cytoplasm
- Inside mitochondria
- In the periplasmic space
Correct Answer: Within the nucleoid region of the cytoplasm
Q28. Horizontal gene transfer mediated by bacteriophages is called:
- Transformation
- Transduction
- Conjugation
- Binary fission
Correct Answer: Transduction
Q29. Which antibiotic inhibits the peptidyl transferase activity of the 50S ribosomal subunit?
- Tetracycline
- Chloramphenicol
- Penicillin
- Ciprofloxacin
Correct Answer: Chloramphenicol
Q30. Quorum sensing in Gram-negative bacteria commonly uses which signaling molecules?
- Autoinducing peptides (AIPs)
- Acyl-homoserine lactones (AHLs)
- cAMP
- Teichoic acids
Correct Answer: Acyl-homoserine lactones (AHLs)
Q31. Which enzyme introduces negative supercoils into bacterial DNA?
- DNA ligase
- DNA gyrase (topoisomerase II)
- RNA polymerase
- Helicase
Correct Answer: DNA gyrase (topoisomerase II)
Q32. The Ziehl–Neelsen stain is used to identify which group of bacteria?
- Gram-positive cocci
- Acid-fast bacteria such as Mycobacterium
- Endospore-forming Bacillus species
- All Gram-negative rods
Correct Answer: Acid-fast bacteria such as Mycobacterium
Q33. Which structural feature helps bacteria evade phagocytosis by host immune cells?
- Endospore cortex
- Capsule
- Ribosomes
- Chromosomal DNA
Correct Answer: Capsule
Q34. Macrolide antibiotics inhibit bacterial protein synthesis by binding to which ribosomal subunit?
- 30S subunit
- 50S subunit and blocking translocation
- Large nucleoid-associated proteins
- Cell membrane enzymes
Correct Answer: 50S subunit and blocking translocation
Q35. Why are many Gram-negative bacteria intrinsically less susceptible to some hydrophobic antibiotics?
- They have thicker peptidoglycan
- Their outer membrane acts as a permeability barrier
- They lack ribosomes
- They have higher mutation rates
Correct Answer: Their outer membrane acts as a permeability barrier
Q36. Which genus lacks a cell wall and is intrinsically resistant to β-lactam antibiotics?
- Staphylococcus
- Mycoplasma
- Escherichia
- Bacillus
Correct Answer: Mycoplasma
Q37. The S-layer found on the surface of some bacteria is composed mainly of:
- Crystalline arrays of protein or glycoprotein providing protection
- Polysaccharide capsules used for nutrient storage
- Lipid bilayers for energy production
- Ribosomal units for protein synthesis
Correct Answer: Crystalline arrays of protein or glycoprotein providing protection
Q38. Which secretion pathway transports unfolded proteins across the cytoplasmic membrane in bacteria?
- Type III secretion system
- Sec pathway
- Tat pathway
- Type I secretion system
Correct Answer: Sec pathway
Q39. Which cytoskeletal protein forms filaments that help segregate plasmids during cell division?
- FtsZ
- MreB
- ParM
- Flagellin
Correct Answer: ParM
Q40. Penicillin-binding proteins (PBPs) are involved in which process?
- DNA replication
- Peptidoglycan synthesis and cross-linking
- Protein folding in the cytoplasm
- LPS assembly in the outer membrane
Correct Answer: Peptidoglycan synthesis and cross-linking
Q41. Sporulation (endospore formation) in Bacillus occurs primarily in response to:
- Excess nutrients and rapid growth
- Nutrient limitation and environmental stress
- High intracellular ATP levels
- Presence of antibiotics
Correct Answer: Nutrient limitation and environmental stress
Q42. After secretion through Sec or Tat pathways, the signal peptide is removed by which enzyme?
- Transpeptidase
- Signal peptidase
- RNase
- DNA polymerase
Correct Answer: Signal peptidase
Q43. Twitching motility in bacteria is mediated primarily by which structure?
- Flagella
- Type IV pili
- Capsule polysaccharides
- Ribosomes
Correct Answer: Type IV pili
Q44. During Gram staining, which reagent acts as the decolorizer?
- Iodine
- Alcohol (ethanol or acetone)
- Crystal violet
- Safranin
Correct Answer: Alcohol (ethanol or acetone)
Q45. Volutin (metachromatic) granules are intracellular stores of which substance?
- Polyphosphate (inorganic phosphate)
- Polyhydroxyalkanoates
- Elemental sulfur
- Iron
Correct Answer: Polyphosphate (inorganic phosphate)
Q46. Which secretion system injects effector proteins directly into eukaryotic host cells in many Gram-negative pathogens?
- Sec pathway
- Type III secretion system
- Type II secretion system
- Tat pathway
Correct Answer: Type III secretion system
Q47. Outer membrane vesicles (OMVs) produced by Gram-negative bacteria typically contain:
- Inner membrane DNA and ribosomes
- Lipopolysaccharide (LPS) and outer membrane proteins
- Endospore core materials
- Glycogen and PHB granules
Correct Answer: Lipopolysaccharide (LPS) and outer membrane proteins
Q48. Which antibiotic class irreversibly inhibits the transpeptidation step of peptidoglycan synthesis?
- Aminoglycosides
- β-lactams
- Tetracyclines
- Macrolides
Correct Answer: β-lactams
Q49. Which microscopy technique is most suitable to visualize bacterial ultrastructure such as flagellar basal bodies and membranes?
- Light microscopy with simple stain
- Transmission electron microscopy (TEM)
- Confocal fluorescence microscopy
- Phase-contrast microscopy
Correct Answer: Transmission electron microscopy (TEM)
Q50. In prokaryotes, where does the electron transport chain for oxidative phosphorylation occur?
- Inner mitochondrial membrane
- Cytoplasmic membrane (plasma membrane)
- Periplasmic space exclusively
- Cell wall peptidoglycan layer
Correct Answer: Cytoplasmic membrane (plasma membrane)
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