BIOL251 Human Anatomy & Physiology I w/Lab 2026 | Module 2 Exam Review v2.0: Advanced
Clinical & Physiological Integration with 150 High-Yield Multiple-Choice Questions Featuring
Multi-Step Clinical Scenarios, Complex Pathway Analysis, Histological Identification, Membrane
Transport Dynamics, Metabolic Regulation, and Gene Expression | LockDown Browser Format |
Portage Learning Curriculum-Aligned | Advanced/Hard Difficulty for Pre-Nursing & Allied
Health Students
SECTION 1: CELLULAR STRUCTURE, ORGANELLES & CYTOSKELETON (Questions 1–25)
🟢 Question 1: A 45-year-old patient presents with progressive muscle weakness, exercise intolerance, and lactic acidosis. A muscle biopsy reveals "ragged
red fibers" on modified Gomori trichrome stain, and electron microscopy shows abnormal mitochondrial cristae with paracrystalline inclusions. Which
organelle's dysfunction is most directly responsible for this patient's constellation of symptoms?
A) Peroxisomal β-oxidation defect
B) Lysosomal acid hydrolase deficiency
C) Mitochondrial oxidative phosphorylation defect
D) Smooth endoplasmic reticulum calcium sequestration failure
🔴 Correct Answer: C) Mitochondrial oxidative phosphorylation defect
Rationale: "Ragged red fibers" are a classic histopathological finding in mitochondrial myopathies, representing subsarcolemmal accumulation of abnormal
mitochondria. The paracrystalline inclusions within cristae indicate structural disruption of the inner mitochondrial membrane, where oxidative
phosphorylation occurs. This directly impairs ATP production, causing muscle weakness and exercise intolerance. Lactic acidosis results from increased
anaerobic glycolysis as cells attempt to compensate for impaired aerobic respiration.
🟢 Question 2: A researcher treats cultured cells with colchicine, a drug that binds to tubulin dimers and prevents their polymerization. Which of the
following cellular processes would be most immediately and severely impaired?
A) Intracellular vesicular transport along microtubule tracks
B) Actin-mediated cytokinesis during cell division
C) Intermediate filament-mediated mechanical support
D) Lysosomal enzyme synthesis in the rough ER
🔴 Correct Answer: A) Intracellular vesicular transport along microtubule tracks
Rationale: Colchicine binds to tubulin dimers, preventing microtubule polymerization. Microtubules form the tracks along which motor proteins (kinesin
and dynein) transport vesicles and organelles. This directly impairs intracellular trafficking. Cytokinesis involves actin microfilaments, intermediate filaments
provide structural support, and lysosomal enzymes are synthesized on rough ER ribosomes—none directly require microtubule polymerization.
🟢 Question 3: A cell is exposed to a toxin that specifically inhibits the function of the Golgi apparatus's trans-Golgi network (TGN). Which of the following
would be the earliest and most direct consequence?
A) Impaired synthesis of transmembrane proteins
B) Failure to sort and package lysosomal enzymes into clathrin-coated vesicles
C) Reduced ATP production
D) Accumulation of unfolded proteins in the ER
🔴 Correct Answer: B) Failure to sort and package lysosomal enzymes into clathrin-coated vesicles
Rationale: The trans-Golgi network (TGN) is the primary sorting station of the Golgi apparatus, where proteins are packaged into specific vesicles for their
final destinations. Lysosomal enzymes are tagged with mannose-6-phosphate in the cis-Golgi and then recognized by receptors in the TGN for packaging
,into clathrin-coated vesicles destined for late endosomes/lysosomes. Transmembrane proteins are synthesized on the rough ER, ATP production occurs in
mitochondria, and unfolded protein accumulation triggers the ER stress response in the ER itself.
🟢 Question 4: Which statement correctly distinguishes between the functions of the rough endoplasmic reticulum (RER) and the smooth endoplasmic
reticulum (SER) in hepatocytes?
A) RER synthesizes steroid hormones; SER synthesizes plasma proteins
B) RER performs detoxification of drugs; SER synthesizes phospholipids
C) RER synthesizes proteins for secretion; SER performs glycogen metabolism and drug detoxification
D) RER stores calcium ions; SER synthesizes lipoproteins
🔴 Correct Answer: C) RER synthesizes proteins for secretion; SER performs glycogen metabolism and drug detoxification
Rationale: In hepatocytes (liver cells), the RER is abundant and synthesizes plasma proteins (e.g., albumin, clotting factors) for secretion. The SER is involved
in glycogen metabolism (glucose-6-phosphatase), drug detoxification (cytochrome P450 system), and lipid synthesis. Steroid hormone synthesis occurs in
the SER of steroid-producing cells (adrenal cortex, gonads), not hepatocytes.
🟢 Question 5: A patient with Zellweger syndrome has a defect in peroxisomal biogenesis, leading to the absence of functional peroxisomes. Which
metabolic abnormality would you most expect to find in this patient?
A) Elevated very-long-chain fatty acids (VLCFAs) and impaired plasmalogen synthesis
B) Lysosomal accumulation of glycosphingolipids
C) Impaired mitochondrial fatty acid β-oxidation
D) Defective protein glycosylation
🔴 Correct Answer: A) Elevated very-long-chain fatty acids (VLCFAs) and impaired plasmalogen synthesis
Rationale: Peroxisomes are essential for the β-oxidation of very-long-chain fatty acids (VLCFAs, >22 carbons) and for the synthesis of plasmalogens (ether
phospholipids critical for myelin and cell membranes). In Zellweger syndrome, peroxisomes are absent, leading to VLCFA accumulation and plasmalogen
deficiency. Lysosomal storage disorders involve glycosphingolipids, mitochondrial β-oxidation defects affect medium-chain fatty acids, and protein
glycosylation occurs in the ER/Golgi.
🟢 Question 6: The nuclear lamina is disassembled during mitosis through phosphorylation of lamin proteins. Which kinase is primarily responsible for this
phosphorylation?
A) Cyclin-dependent kinase 1 (CDK1)/cyclin B
B) Protein kinase A (PKA)
C) DNA-dependent protein kinase (DNA-PK)
D) AMP-activated protein kinase (AMPK)
🔴 Correct Answer: A) Cyclin-dependent kinase 1 (CDK1)/cyclin B
Rationale: CDK1 (formerly CDC2) in complex with cyclin B phosphorylates nuclear lamins at specific serine residues, triggering depolymerization of the
nuclear lamina and nuclear envelope breakdown during prophase of mitosis. This allows access of the mitotic spindle to chromosomes.
🟢 Question 7: A cell is treated with brefeldin A, a fungal metabolite that inhibits ARF-GEF (guanine nucleotide exchange factor) and causes the Golgi
apparatus to disassemble and fuse with the ER. Which transport pathway would be most directly disrupted?
A) Endocytosis from the plasma membrane to early endosomes
B) Retrograde transport from the Golgi to the ER
C) Anterograde transport from the ER to the Golgi
D) Exocytosis from the Golgi to the plasma membrane
🔴 Correct Answer: C) Anterograde transport from the ER to the Golgi
,Rationale: Brefeldin A inhibits the ARF-GEF required for COPI coat assembly, which is essential for retrograde transport from the Golgi to the ER. However,
by disrupting the Golgi structure entirely (causing it to fuse with the ER), it also effectively blocks anterograde ER-to-Golgi transport. The most direct effect
is the collapse of the Golgi into the ER, preventing the normal flow of proteins from ER through the Golgi. Endocytosis and exocytosis involve different coat
proteins (clathrin).
🟢 Question 8: Which cytoskeletal element is composed of a family of related proteins (at least 70 different types) and provides the most stable, long-term
structural support for cells and tissues?
A) Microtubules
B) Microfilaments
C) Intermediate filaments
D) Septins
🔴 Correct Answer: C) Intermediate filaments
Rationale: Intermediate filaments are composed of a large family of proteins (keratins, vimentin, desmin, neurofilaments, lamins) and are the most stable
cytoskeletal elements. They provide long-term mechanical support, resist tension, and maintain cell shape. Microtubules and microfilaments are more
dynamic and involved in motility and transport.
🟢 Question 9: A patient with a mutation in the gene encoding the lysosomal-associated membrane protein 2 (LAMP-2) presents with Danon disease,
characterized by cardiomyopathy, myopathy, and intellectual disability. What is the primary function of LAMP-2 that, when impaired, leads to this disease?
A) Synthesis of lysosomal hydrolases
B) Fusion of lysosomes with autophagosomes (autophagy)
C) Acidification of the lysosomal lumen
D) Sorting of mannose-6-phosphate receptors
🔴 Correct Answer: B) Fusion of lysosomes with autophagosomes (autophagy)
Rationale: LAMP-2 is a lysosomal membrane protein that plays a critical role in chaperone-mediated autophagy and in the fusion of lysosomes with
autophagosomes (macroautophagy). Defective autophagy leads to accumulation of autophagic vacuoles in cardiac and skeletal muscle, causing the clinical
features of Danon disease. Lysosomal hydrolases are synthesized in the ER, acidification is mediated by the V-ATPase, and mannose-6-phosphate receptor
sorting occurs in the Golgi.
🟢 Question 10: The mitochondrial matrix contains a unique DNA molecule that encodes:
A) All mitochondrial proteins
B) 13 proteins essential for oxidative phosphorylation, plus tRNAs and rRNAs
C) Only the electron transport chain complexes
D) The entire mitochondrial genome including all metabolic enzymes
🔴 Correct Answer: B) 13 proteins essential for oxidative phosphorylation, plus tRNAs and rRNAs
Rationale: Human mitochondrial DNA (mtDNA) is a circular molecule of approximately 16.5 kb that encodes 13 protein subunits of the electron transport
chain and ATP synthase, along with 22 tRNAs and 2 rRNAs required for mitochondrial protein synthesis. The majority of mitochondrial proteins
(approximately 1,000) are encoded by nuclear DNA and imported into the mitochondria.
🟢 Question 11: A cell with a defect in the dynein motor protein would have impaired movement of cargo in which direction along microtubules?
A) Toward the plus end (anterograde, toward the cell periphery)
B) Toward the minus end (retrograde, toward the microtubule-organizing center)
C) Bidirectional movement with equal impairment in both directions
D) No effect on microtubule-based transport
🔴 Correct Answer: B) Toward the minus end (retrograde, toward the microtubule-organizing center)
, Rationale: Dynein is a minus-end-directed microtubule motor protein that transports cargo toward the microtubule-organizing center (MTOC, usually near
the nucleus). Kinesin is the plus-end-directed motor that transports cargo toward the cell periphery. Dynein is responsible for retrograde transport of
vesicles, organelles, and proteins from the axon terminal back to the cell body in neurons.
🟢 Question 12: Which of the following correctly describes the role of the proteasome in cellular protein quality control?
A) It degrades proteins in lysosomes through acid hydrolases
B) It ubiquitinates misfolded proteins for ER-associated degradation
C) It degrades ubiquitinated proteins through ATP-dependent proteolysis in the cytosol and nucleus
D) It folds proteins with the assistance of chaperones
🔴 Correct Answer: C) It degrades ubiquitinated proteins through ATP-dependent proteolysis in the cytosol and nucleus
Rationale: The proteasome is a large, ATP-dependent protease complex in the cytosol and nucleus that degrades proteins tagged with ubiquitin chains.
This is the primary pathway for degradation of misfolded, damaged, or regulatory proteins. Lysosomes degrade proteins through autophagy.
Ubiquitination is catalyzed by ubiquitin ligases (E3), not the proteasome itself. Chaperones assist in protein folding.
🟢 Question 13: A researcher observes that a particular cell type has an exceptionally large nucleolus. This observation most likely indicates that the cell:
A) Is undergoing apoptosis
B) Has high rates of ribosomal RNA synthesis and ribosome assembly
C) Has a defect in mRNA splicing
D) Is in the G0 phase of the cell cycle
🔴 Correct Answer: B) Has high rates of ribosomal RNA synthesis and ribosome assembly
Rationale: The nucleolus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly. A prominent nucleolus indicates high transcriptional activity
of rRNA genes and high demand for protein synthesis, characteristic of cells that are actively growing, dividing, or secreting proteins (e.g., cancer cells,
embryonic cells, plasma cells). Apoptosis involves nucleolar fragmentation, and mRNA splicing occurs in nuclear speckles, not the nucleolus.
🟢 Question 14: A patient has a defect in the enzyme catalase, which is normally found in peroxisomes. Which of the following would be the most direct
consequence?
A) Accumulation of very-long-chain fatty acids
B) Impaired breakdown of hydrogen peroxide (H₂O₂)
C) Reduced synthesis of plasmalogens
D) Impaired bile acid synthesis
🔴 Correct Answer: B) Impaired breakdown of hydrogen peroxide (H₂O₂)
Rationale: Catalase is a peroxisomal enzyme that catalyzes the breakdown of hydrogen peroxide (2 H₂O₂ → 2 H₂O + O₂), which is generated as a byproduct
of oxidative reactions in peroxisomes (e.g., fatty acid oxidation). Defective catalase would lead to accumulation of toxic H₂O₂. VLCFA accumulation,
plasmalogen synthesis defects, and bile acid synthesis defects are caused by other peroxisomal enzyme deficiencies.
🟢 Question 15: The endoplasmic reticulum (ER) stress response, also known as the unfolded protein response (UPR), is activated when:
A) The ER lumen becomes depleted of calcium
B) Misfolded proteins accumulate in the ER lumen
C) The Golgi apparatus fails to glycosylate proteins
D) Mitochondrial ATP production decreases
🔴 Correct Answer: B) Misfolded proteins accumulate in the ER lumen
Rationale: The unfolded protein response (UPR) is a cellular stress response activated when misfolded or unfolded proteins accumulate in the ER lumen.
The UPR aims to restore ER homeostasis by reducing protein synthesis, increasing ER chaperone production, and enhancing ER-associated degradation
(ERAD) of misfolded proteins. If the stress is unresolvable, the UPR triggers apoptosis.
Clinical & Physiological Integration with 150 High-Yield Multiple-Choice Questions Featuring
Multi-Step Clinical Scenarios, Complex Pathway Analysis, Histological Identification, Membrane
Transport Dynamics, Metabolic Regulation, and Gene Expression | LockDown Browser Format |
Portage Learning Curriculum-Aligned | Advanced/Hard Difficulty for Pre-Nursing & Allied
Health Students
SECTION 1: CELLULAR STRUCTURE, ORGANELLES & CYTOSKELETON (Questions 1–25)
🟢 Question 1: A 45-year-old patient presents with progressive muscle weakness, exercise intolerance, and lactic acidosis. A muscle biopsy reveals "ragged
red fibers" on modified Gomori trichrome stain, and electron microscopy shows abnormal mitochondrial cristae with paracrystalline inclusions. Which
organelle's dysfunction is most directly responsible for this patient's constellation of symptoms?
A) Peroxisomal β-oxidation defect
B) Lysosomal acid hydrolase deficiency
C) Mitochondrial oxidative phosphorylation defect
D) Smooth endoplasmic reticulum calcium sequestration failure
🔴 Correct Answer: C) Mitochondrial oxidative phosphorylation defect
Rationale: "Ragged red fibers" are a classic histopathological finding in mitochondrial myopathies, representing subsarcolemmal accumulation of abnormal
mitochondria. The paracrystalline inclusions within cristae indicate structural disruption of the inner mitochondrial membrane, where oxidative
phosphorylation occurs. This directly impairs ATP production, causing muscle weakness and exercise intolerance. Lactic acidosis results from increased
anaerobic glycolysis as cells attempt to compensate for impaired aerobic respiration.
🟢 Question 2: A researcher treats cultured cells with colchicine, a drug that binds to tubulin dimers and prevents their polymerization. Which of the
following cellular processes would be most immediately and severely impaired?
A) Intracellular vesicular transport along microtubule tracks
B) Actin-mediated cytokinesis during cell division
C) Intermediate filament-mediated mechanical support
D) Lysosomal enzyme synthesis in the rough ER
🔴 Correct Answer: A) Intracellular vesicular transport along microtubule tracks
Rationale: Colchicine binds to tubulin dimers, preventing microtubule polymerization. Microtubules form the tracks along which motor proteins (kinesin
and dynein) transport vesicles and organelles. This directly impairs intracellular trafficking. Cytokinesis involves actin microfilaments, intermediate filaments
provide structural support, and lysosomal enzymes are synthesized on rough ER ribosomes—none directly require microtubule polymerization.
🟢 Question 3: A cell is exposed to a toxin that specifically inhibits the function of the Golgi apparatus's trans-Golgi network (TGN). Which of the following
would be the earliest and most direct consequence?
A) Impaired synthesis of transmembrane proteins
B) Failure to sort and package lysosomal enzymes into clathrin-coated vesicles
C) Reduced ATP production
D) Accumulation of unfolded proteins in the ER
🔴 Correct Answer: B) Failure to sort and package lysosomal enzymes into clathrin-coated vesicles
Rationale: The trans-Golgi network (TGN) is the primary sorting station of the Golgi apparatus, where proteins are packaged into specific vesicles for their
final destinations. Lysosomal enzymes are tagged with mannose-6-phosphate in the cis-Golgi and then recognized by receptors in the TGN for packaging
,into clathrin-coated vesicles destined for late endosomes/lysosomes. Transmembrane proteins are synthesized on the rough ER, ATP production occurs in
mitochondria, and unfolded protein accumulation triggers the ER stress response in the ER itself.
🟢 Question 4: Which statement correctly distinguishes between the functions of the rough endoplasmic reticulum (RER) and the smooth endoplasmic
reticulum (SER) in hepatocytes?
A) RER synthesizes steroid hormones; SER synthesizes plasma proteins
B) RER performs detoxification of drugs; SER synthesizes phospholipids
C) RER synthesizes proteins for secretion; SER performs glycogen metabolism and drug detoxification
D) RER stores calcium ions; SER synthesizes lipoproteins
🔴 Correct Answer: C) RER synthesizes proteins for secretion; SER performs glycogen metabolism and drug detoxification
Rationale: In hepatocytes (liver cells), the RER is abundant and synthesizes plasma proteins (e.g., albumin, clotting factors) for secretion. The SER is involved
in glycogen metabolism (glucose-6-phosphatase), drug detoxification (cytochrome P450 system), and lipid synthesis. Steroid hormone synthesis occurs in
the SER of steroid-producing cells (adrenal cortex, gonads), not hepatocytes.
🟢 Question 5: A patient with Zellweger syndrome has a defect in peroxisomal biogenesis, leading to the absence of functional peroxisomes. Which
metabolic abnormality would you most expect to find in this patient?
A) Elevated very-long-chain fatty acids (VLCFAs) and impaired plasmalogen synthesis
B) Lysosomal accumulation of glycosphingolipids
C) Impaired mitochondrial fatty acid β-oxidation
D) Defective protein glycosylation
🔴 Correct Answer: A) Elevated very-long-chain fatty acids (VLCFAs) and impaired plasmalogen synthesis
Rationale: Peroxisomes are essential for the β-oxidation of very-long-chain fatty acids (VLCFAs, >22 carbons) and for the synthesis of plasmalogens (ether
phospholipids critical for myelin and cell membranes). In Zellweger syndrome, peroxisomes are absent, leading to VLCFA accumulation and plasmalogen
deficiency. Lysosomal storage disorders involve glycosphingolipids, mitochondrial β-oxidation defects affect medium-chain fatty acids, and protein
glycosylation occurs in the ER/Golgi.
🟢 Question 6: The nuclear lamina is disassembled during mitosis through phosphorylation of lamin proteins. Which kinase is primarily responsible for this
phosphorylation?
A) Cyclin-dependent kinase 1 (CDK1)/cyclin B
B) Protein kinase A (PKA)
C) DNA-dependent protein kinase (DNA-PK)
D) AMP-activated protein kinase (AMPK)
🔴 Correct Answer: A) Cyclin-dependent kinase 1 (CDK1)/cyclin B
Rationale: CDK1 (formerly CDC2) in complex with cyclin B phosphorylates nuclear lamins at specific serine residues, triggering depolymerization of the
nuclear lamina and nuclear envelope breakdown during prophase of mitosis. This allows access of the mitotic spindle to chromosomes.
🟢 Question 7: A cell is treated with brefeldin A, a fungal metabolite that inhibits ARF-GEF (guanine nucleotide exchange factor) and causes the Golgi
apparatus to disassemble and fuse with the ER. Which transport pathway would be most directly disrupted?
A) Endocytosis from the plasma membrane to early endosomes
B) Retrograde transport from the Golgi to the ER
C) Anterograde transport from the ER to the Golgi
D) Exocytosis from the Golgi to the plasma membrane
🔴 Correct Answer: C) Anterograde transport from the ER to the Golgi
,Rationale: Brefeldin A inhibits the ARF-GEF required for COPI coat assembly, which is essential for retrograde transport from the Golgi to the ER. However,
by disrupting the Golgi structure entirely (causing it to fuse with the ER), it also effectively blocks anterograde ER-to-Golgi transport. The most direct effect
is the collapse of the Golgi into the ER, preventing the normal flow of proteins from ER through the Golgi. Endocytosis and exocytosis involve different coat
proteins (clathrin).
🟢 Question 8: Which cytoskeletal element is composed of a family of related proteins (at least 70 different types) and provides the most stable, long-term
structural support for cells and tissues?
A) Microtubules
B) Microfilaments
C) Intermediate filaments
D) Septins
🔴 Correct Answer: C) Intermediate filaments
Rationale: Intermediate filaments are composed of a large family of proteins (keratins, vimentin, desmin, neurofilaments, lamins) and are the most stable
cytoskeletal elements. They provide long-term mechanical support, resist tension, and maintain cell shape. Microtubules and microfilaments are more
dynamic and involved in motility and transport.
🟢 Question 9: A patient with a mutation in the gene encoding the lysosomal-associated membrane protein 2 (LAMP-2) presents with Danon disease,
characterized by cardiomyopathy, myopathy, and intellectual disability. What is the primary function of LAMP-2 that, when impaired, leads to this disease?
A) Synthesis of lysosomal hydrolases
B) Fusion of lysosomes with autophagosomes (autophagy)
C) Acidification of the lysosomal lumen
D) Sorting of mannose-6-phosphate receptors
🔴 Correct Answer: B) Fusion of lysosomes with autophagosomes (autophagy)
Rationale: LAMP-2 is a lysosomal membrane protein that plays a critical role in chaperone-mediated autophagy and in the fusion of lysosomes with
autophagosomes (macroautophagy). Defective autophagy leads to accumulation of autophagic vacuoles in cardiac and skeletal muscle, causing the clinical
features of Danon disease. Lysosomal hydrolases are synthesized in the ER, acidification is mediated by the V-ATPase, and mannose-6-phosphate receptor
sorting occurs in the Golgi.
🟢 Question 10: The mitochondrial matrix contains a unique DNA molecule that encodes:
A) All mitochondrial proteins
B) 13 proteins essential for oxidative phosphorylation, plus tRNAs and rRNAs
C) Only the electron transport chain complexes
D) The entire mitochondrial genome including all metabolic enzymes
🔴 Correct Answer: B) 13 proteins essential for oxidative phosphorylation, plus tRNAs and rRNAs
Rationale: Human mitochondrial DNA (mtDNA) is a circular molecule of approximately 16.5 kb that encodes 13 protein subunits of the electron transport
chain and ATP synthase, along with 22 tRNAs and 2 rRNAs required for mitochondrial protein synthesis. The majority of mitochondrial proteins
(approximately 1,000) are encoded by nuclear DNA and imported into the mitochondria.
🟢 Question 11: A cell with a defect in the dynein motor protein would have impaired movement of cargo in which direction along microtubules?
A) Toward the plus end (anterograde, toward the cell periphery)
B) Toward the minus end (retrograde, toward the microtubule-organizing center)
C) Bidirectional movement with equal impairment in both directions
D) No effect on microtubule-based transport
🔴 Correct Answer: B) Toward the minus end (retrograde, toward the microtubule-organizing center)
, Rationale: Dynein is a minus-end-directed microtubule motor protein that transports cargo toward the microtubule-organizing center (MTOC, usually near
the nucleus). Kinesin is the plus-end-directed motor that transports cargo toward the cell periphery. Dynein is responsible for retrograde transport of
vesicles, organelles, and proteins from the axon terminal back to the cell body in neurons.
🟢 Question 12: Which of the following correctly describes the role of the proteasome in cellular protein quality control?
A) It degrades proteins in lysosomes through acid hydrolases
B) It ubiquitinates misfolded proteins for ER-associated degradation
C) It degrades ubiquitinated proteins through ATP-dependent proteolysis in the cytosol and nucleus
D) It folds proteins with the assistance of chaperones
🔴 Correct Answer: C) It degrades ubiquitinated proteins through ATP-dependent proteolysis in the cytosol and nucleus
Rationale: The proteasome is a large, ATP-dependent protease complex in the cytosol and nucleus that degrades proteins tagged with ubiquitin chains.
This is the primary pathway for degradation of misfolded, damaged, or regulatory proteins. Lysosomes degrade proteins through autophagy.
Ubiquitination is catalyzed by ubiquitin ligases (E3), not the proteasome itself. Chaperones assist in protein folding.
🟢 Question 13: A researcher observes that a particular cell type has an exceptionally large nucleolus. This observation most likely indicates that the cell:
A) Is undergoing apoptosis
B) Has high rates of ribosomal RNA synthesis and ribosome assembly
C) Has a defect in mRNA splicing
D) Is in the G0 phase of the cell cycle
🔴 Correct Answer: B) Has high rates of ribosomal RNA synthesis and ribosome assembly
Rationale: The nucleolus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly. A prominent nucleolus indicates high transcriptional activity
of rRNA genes and high demand for protein synthesis, characteristic of cells that are actively growing, dividing, or secreting proteins (e.g., cancer cells,
embryonic cells, plasma cells). Apoptosis involves nucleolar fragmentation, and mRNA splicing occurs in nuclear speckles, not the nucleolus.
🟢 Question 14: A patient has a defect in the enzyme catalase, which is normally found in peroxisomes. Which of the following would be the most direct
consequence?
A) Accumulation of very-long-chain fatty acids
B) Impaired breakdown of hydrogen peroxide (H₂O₂)
C) Reduced synthesis of plasmalogens
D) Impaired bile acid synthesis
🔴 Correct Answer: B) Impaired breakdown of hydrogen peroxide (H₂O₂)
Rationale: Catalase is a peroxisomal enzyme that catalyzes the breakdown of hydrogen peroxide (2 H₂O₂ → 2 H₂O + O₂), which is generated as a byproduct
of oxidative reactions in peroxisomes (e.g., fatty acid oxidation). Defective catalase would lead to accumulation of toxic H₂O₂. VLCFA accumulation,
plasmalogen synthesis defects, and bile acid synthesis defects are caused by other peroxisomal enzyme deficiencies.
🟢 Question 15: The endoplasmic reticulum (ER) stress response, also known as the unfolded protein response (UPR), is activated when:
A) The ER lumen becomes depleted of calcium
B) Misfolded proteins accumulate in the ER lumen
C) The Golgi apparatus fails to glycosylate proteins
D) Mitochondrial ATP production decreases
🔴 Correct Answer: B) Misfolded proteins accumulate in the ER lumen
Rationale: The unfolded protein response (UPR) is a cellular stress response activated when misfolded or unfolded proteins accumulate in the ER lumen.
The UPR aims to restore ER homeostasis by reducing protein synthesis, increasing ER chaperone production, and enhancing ER-associated degradation
(ERAD) of misfolded proteins. If the stress is unresolvable, the UPR triggers apoptosis.
