Cell biology: cell structure and organelle functions MCQs With Answer

Introduction

This MCQ set on Cell biology: cell structure and organelle functions is tailored for M.Pharm students preparing for advanced exams in Cellular and Molecular Pharmacology. The questions probe not only structural features of organelles but also their biochemical roles, intracellular trafficking, and pharmacological relevance — for example, how drugs affect mitochondrial respiration, proteasomal function, lysosomal degradation, and cytochrome P450 activity. Each item assesses conceptual understanding and the ability to apply knowledge to drug action, targeted delivery, and cellular homeostasis. Use these MCQs to deepen your mechanistic insight and to practice reasoning about organelle-targeted therapies and cellular responses to pharmacological interventions.

Q1. Which mitochondrial compartment houses the enzymes of the tricarboxylic acid (TCA) cycle?

• Intermembrane space
• Inner membrane
• Matrix
• Cristae lumen

Correct Answer: Matrix

Q2. Which of the following best describes the primary role of the rough endoplasmic reticulum (RER)?

• Synthesis of membrane lipids and steroid hormones
• Protein folding and co-translational translocation into the ER lumen
• Processing and packaging of secretory proteins into vesicles
• Degradation of misfolded proteins via autophagy

Correct Answer: Protein folding and co-translational translocation into the ER lumen

Q3. Which vesicle-coating protein is primarily responsible for anterograde transport from the ER to the Golgi?

• COPI
• Caveolin
• Clathrin
• COPII

Correct Answer: COPII

Q4. Mannose-6-phosphate is a critical signal for trafficking of lysosomal hydrolases. Where is this modification added?

• Golgi apparatus (cis-Golgi network)
• Golgi apparatus (medial cisternae)
• Endoplasmic reticulum lumen
• Trans-Golgi network

Correct Answer: Golgi apparatus (medial cisternae)

Q5. Which structure is the main site of cellular detoxification by cytochrome P450 enzymes?

• Rough endoplasmic reticulum
• Smooth endoplasmic reticulum
• Golgi apparatus
• Peroxisome

Correct Answer: Smooth endoplasmic reticulum

Q6. The 26S proteasome primarily degrades which class of proteins?

• Membrane proteins delivered via lysosomes
• Proteins tagged with ubiquitin chains in the cytosol and nucleus
• Mitochondrial matrix proteins encoded by mtDNA
• Extracellular matrix proteins

Correct Answer: Proteins tagged with ubiquitin chains in the cytosol and nucleus

Q7. Which of the following organelles contains catalase and enzymes for beta-oxidation of very long chain fatty acids?

• Lysosome
• Peroxisome
• Endosome
• Mitochondrion

Correct Answer: Peroxisome

Q8. Which statement best explains how an uncoupler like 2,4-dinitrophenol (DNP) affects oxidative phosphorylation?

• Inhibits electron transport at complex I, stopping proton pumping
• Blocks ATP synthase rotor, preventing ATP synthesis
• Permits protons to bypass ATP synthase, dissipating the proton motive force
• Enhances ADP phosphorylation by increasing membrane potential

Correct Answer: Permits protons to bypass ATP synthase, dissipating the proton motive force

Q9. Which cytoskeletal component provides tracks for kinesin and dynein motor proteins to mediate long-range vesicular transport?

• Actin filaments (microfilaments)
• Intermediate filaments
• Microtubules
• Myosin filaments

Correct Answer: Microtubules

Q10. Which feature differentiates secretory proteins that are co-translationally imported into the ER from those translated in the cytosol?

• Presence of an N-terminal mitochondrial targeting sequence
• Presence of an N-terminal signal peptide recognized by the signal recognition particle
• Polyubiquitination on lysine residues
• Attachment of a C-terminal peroxisomal targeting tripeptide

Correct Answer: Presence of an N-terminal signal peptide recognized by the signal recognition particle

Q11. In the Golgi apparatus, which modification is most commonly completed in the trans-Golgi network prior to secretion?

• N-linked glycosylation initiation
• O-linked glycosylation completion and sorting to final destinations
• Addition of signal peptides
• Protein translation

Correct Answer: O-linked glycosylation completion and sorting to final destinations

Q12. Which organelle is primarily responsible for bulk degradation of cytoplasmic components during nutrient deprivation via autophagy?

• Lysosome
• Proteasome
• Golgi apparatus
• Endoplasmic reticulum

Correct Answer: Lysosome

Q13. Which protein complex or factor recognizes and temporarily halts translation of nascent polypeptides destined for the ER?

• Ubiquitin-conjugating enzyme (E2)
• Signal recognition particle (SRP)
• Chaperonin GroEL
• Clathrin adaptor protein complex

Correct Answer: Signal recognition particle (SRP)

Q14. A drug inhibits complex III of the mitochondrial electron transport chain. Which of the following is the most likely immediate effect?

• Increased proton pumping by complexes I and II
• Decreased electron flow from ubiquinol to cytochrome c, reduced ATP synthesis
• Enhanced ATP generation due to alternative pathways
• Unchanged oxygen consumption

Correct Answer: Decreased electron flow from ubiquinol to cytochrome c, reduced ATP synthesis

Q15. Which targeting signal typically directs newly synthesized proteins to peroxisomes?

• N-terminal signal peptide cleaved upon import
• C-terminal tripeptide SKL (Ser-Lys-Leu) or variant (PTS1)
• Mannose-6-phosphate tag
• Ubiquitin-like modifier (SUMO)

Correct Answer: C-terminal tripeptide SKL (Ser-Lys-Leu) or variant (PTS1)

Q16. Which organelle contains its own circular DNA and ribosomes similar to bacterial 70S ribosomes?

• Endoplasmic reticulum
• Golgi apparatus
• Mitochondrion
• Nucleus

Correct Answer: Mitochondrion

Q17. Which process explains how integral membrane proteins are oriented and integrated into the ER membrane during synthesis?

• Post-translational import via TOM/TIM complexes
• Signal-anchor sequences and translocon (Sec61)-mediated lateral gating
• Coating by clathrin followed by vesicular fusion
• Direct diffusion through the lipid bilayer after synthesis

Correct Answer: Signal-anchor sequences and translocon (Sec61)-mediated lateral gating

Q18. Which lysosomal storage disorder results from deficiency of glucocerebrosidase and commonly affects macrophages and bone marrow?

• Fabry disease
• Tay-Sachs disease
• Gaucher disease
• Niemann-Pick disease type A

Correct Answer: Gaucher disease

Q19. Which molecular event is a key step in intrinsic apoptosis mediated by mitochondria?

• Activation of receptor tyrosine kinases at the plasma membrane
• Release of cytochrome c into the cytosol and apoptosome formation
• Lysosomal membrane stabilization and decreased cathepsin activity
• Ubiquitination of membrane proteins and proteasomal degradation

Correct Answer: Release of cytochrome c into the cytosol and apoptosome formation

Q20. Which endocytic pathway is most commonly exploited by cells to internalize LDL particles via LDL receptor-mediated uptake?

• Caveolin-dependent endocytosis
• Clathrin-mediated endocytosis
• Macropinocytosis
• Phagocytosis

Correct Answer: Clathrin-mediated endocytosis

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