MCB 1
MCB 2
Physio
Anatomy
Biostats
100
Plasma Membrane & Nucleus
A newly synthesized protein contains a nuclear localization signal (NLS) and must enter the nucleus through a nuclear pore complex. Which protein is primarily responsible for recognizing the NLS and facilitating nuclear import?
A. Exportin
B. Importin
C. Clathrin
D. Dynamin
E. Synaptotagmin
Correct answer: B. Importin
Importins recognize nuclear localization signals and mediate nuclear import. Exportins are involved in nuclear export. The Slusarz Q&A emphasized distinguishing importins from exportins.
Concept Tested: Importins and nuclear localization signals
100
Lysosomes & Peroxisomes
A cell is unable to properly deliver several newly synthesized lysosomal hydrolases to lysosomes because a key sorting signal is missing. Which modification is most likely defective?
A. Addition of mannose-6-phosphate
B. Addition of a nuclear localization signal
C. Binding of catalase to hydrogen peroxide
D. Assembly of actin filaments
E. Formation of a mitochondrial proton gradient
Correct answer: A. Addition of mannose-6-phosphate
Mannose-6-phosphate is a lysosomal targeting signal. Its absence interferes with proper delivery of lysosomal enzymes. This targeting defect was highlighted in the lysosomes/peroxisomes Q&A.
Concept Tested: Mannose-6-phosphate and lysosomal targeting
100
A researcher studies a membrane permeable to glucose. Initially, glucose concentrations are 40 mg/mL on one side and 10 mg/mL on the other. The membrane surface area is doubled while its thickness is also doubled. The concentration gradient remains unchanged. What happens to the rate of glucose diffusion?
A. Increases fourfold
B. Doubles
C. Remains unchanged
D. Decreases by half
E. Decreases fourfold
Correct answer: C. Remains unchanged
According to Fick's law, diffusion increases with surface area and decreases with membrane thickness. Doubling both cancels out, leaving diffusion unchanged.
100
A patient is brought to the emergency department after a motor vehicle collision. Imaging reveals fractures of the left 9th–11th ribs and internal bleeding in the left upper abdominal quadrant. Which organ is most likely injured?
A. Liver
B. Spleen
C. Gallbladder
D. Cecum
E. Appendix
Correct answer: B. Spleen
The spleen lies in the left upper quadrant and is protected by ribs 9–11. Your GI lecture specifically highlighted this trauma association.
100
A research team wants to investigate whether long-term exposure to industrial pesticides increases the risk of developing Parkinson's disease. Researchers identify 250 patients already diagnosed with Parkinson's disease and 250 individuals without the disease. They review occupational histories from the previous 20 years to compare pesticide exposure.
Which study design is being used?
A. Retrospective cohort study
B. Prospective cohort study
C. Case-control study
D. Cross-sectional study
E. Randomized controlled trial
Correct answer: C. Case-control study
Participants are selected based on whether they already have the disease, and researchers look backward to assess exposure. Case-control studies commonly report odds ratios.The tricky distinction: a retrospective cohort starts with past exposure status, whereas a case-control study starts with disease status.
200
ER & Golgi
A secretory protein enters the rough endoplasmic reticulum and undergoes its initial N-linked glycosylation. Which statement correctly identifies where this modification begins?
A. In the nucleus before transcription
B. In the cytosol after translation
C. In the rough ER during protein synthesis and processing
D. Only after secretion from the cell
E. Exclusively in lysosomes
Correct answer: C. In the rough ER during protein synthesis and processing
Initial N-linked glycosylation begins in the rough ER. The Golgi can subsequently modify the attached carbohydrate chains. Your ER/Golgi Q&A specifically emphasized the initial location
Concept Tested: N-linked glycosylation in the rough ER
200
Extracellular Matrix, Collagen Defects & Cell Interactions
A patient with prolonged vitamin C deficiency develops impaired wound healing and fragile connective tissues. Which step in collagen synthesis is most directly affected?
A. Translation of collagen mRNA
B. Hydroxylation of proline and lysine residues
C. Transcription of elastin genes
D. Binding of integrins to fibronectin
E. Breakdown of collagen by lysosomes
Correct answer: B. Hydroxylation of proline and lysine residues
Vitamin C is required for hydroxylation of proline and lysine residues during collagen synthesis. Deficiency impairs collagen stability and is associated with scurvy, which your ECM lecture highlighted.
Concept Tested: Vitamin C, collagen hydroxylation, and scurvy
200
A 62-year-old patient with renal failure develops hyperkalemia. A researcher finds that the potassium equilibrium potential becomes less negative and the resting membrane potential shifts closer to threshold. Which change most directly explains this initial effect?
A. Increased potassium efflux due to a larger concentration gradient
B. Decreased potassium efflux due to a reduced concentration gradient
C. Increased sodium-potassium ATPase activity directly generating action potentials
D. Increased chloride influx causing depolarization
E. Complete inactivation of voltage-gated potassium channels
Correct answer: B. Decreased potassium efflux due to a reduced concentration gradient
Increased extracellular K⁺ reduces the outward concentration gradient for K⁺. Less K⁺ leaves the cell, making its resting membrane potential less negative and initially bringing it closer to threshold.
200
A patient develops severe flank pain, and imaging shows a kidney stone lodged in a ureter. Which statement best explains why stones commonly become trapped at particular locations along this structure?
A. The ureter contains valves that prevent urine reflux
B. The ureter has three normal anatomical constrictions
C. The ureter empties directly into the urethra
D. The ureter is located entirely within the pelvic cavity
E. The ureter is a solid cord without smooth muscle
Correct answer: B. The ureter has three normal anatomical constrictions
The renal OLM emphasizes that ureters are smooth-muscle tubes with three normal constrictions, where stones may become lodged.
200
A randomized clinical trial evaluates a new medication for hypertension. Participants are assigned to either the treatment group or the placebo group. During the study, 30% of participants assigned to the medication discontinue it because of side effects. Researchers analyze outcomes according to the treatment each participant actually received, rather than their original assignment.
Which statement best describes the consequence of this analysis?
A. It is an intention-to-treat analysis that preserves randomization.
B. It is a per-protocol analysis that may introduce bias by disrupting the benefits of randomization.
C. It is a case-control analysis that reports an odds ratio.
D. It is an intention-to-treat analysis that measures real-world adherence.
E. It is a cross-sectional analysis that evaluates prevalence.
Correct answer: B. Per-protocol analysis
Per-protocol (as-treated) analysis considers treatment actually received and may compromise the original randomization.Intention-to-treat analyzes patients in their originally assigned groups, regardless of adherence, helping preserve randomization and reduce bias.
300
Exocytosis & Endocytosis
A mutation prevents synaptotagmin from responding to increased intracellular Ca²⁺ in a presynaptic nerve terminal. Vesicle docking proteins are otherwise functional. Which event is most directly impaired?
A. Clathrin-coated pit formation
B. Vesicle transport into the nucleus
C. Ca²⁺-triggered synaptic vesicle fusion
D. Mitochondrial ATP synthesis
E. Mannose-6-phosphate addition
Correct answer: C. Ca²⁺-triggered synaptic vesicle fusion
Synaptotagmin acts as a Ca²⁺ sensor for regulated exocytosis. The SNARE machinery brings membranes together, while the Ca²⁺ signal triggers fusion.
Concept Tested: Synaptotagmin and Ca²⁺-triggered vesicle fusion
300
pH & Acid–Base Balance
A patient with prolonged diarrhea has an arterial pH of 7.28, decreased plasma HCO₃⁻, and decreased PCO₂. Which interpretation best explains the findings?
A. Respiratory acidosis with renal compensation
B. Respiratory alkalosis with renal compensation
C. Metabolic alkalosis with respiratory compensation
D. Metabolic acidosis with respiratory compensation
E. Mixed respiratory and metabolic alkalosis
Correct answer: D. Metabolic acidosis with respiratory compensation
Diarrhea can cause bicarbonate loss, producing metabolic acidosis. Hyperventilation lowers PCO₂ as respiratory compensation. The low pH shows that acidemia persists despite compensation.
Concept Tested: Metabolic acidosis and respiratory compensation
300
An experimental toxin prevents synaptotagmin from responding to calcium at the presynaptic terminal. Action potentials arrive normally, and voltage-gated calcium channels still open. Which process will be most directly impaired?
A. Propagation of action potentials along the axon
B. Calcium entry into the presynaptic terminal
C. Calcium-triggered fusion of synaptic vesicles with the presynaptic membrane
D. Binding of neurotransmitters to postsynaptic receptors
E. Generation of the resting membrane potential
Correct answer: C. Calcium-triggered fusion of synaptic vesicles with the presynaptic membrane
Synaptotagmin acts as the calcium sensor for vesicle fusion. Calcium can still enter, but the signal cannot effectively trigger SNARE-mediated vesicle fusion and neurotransmitter exocytosis.
300
A patient has impaired production of aldosterone but normal cortisol and adrenal androgen production. Which region of the adrenal gland is most directly affected?
A. Zona fasciculata
B. Zona reticularis
C. Adrenal medulla
D. Zona glomerulosa
E. Posterior pituitary
Correct answer: D. Zona glomerulosa
The zona glomerulosa secretes aldosterone, the zona fasciculata secretes cortisol, the zona reticularis produces weak androgens, and the medulla produces epinephrine and norepinephrine.
300
Question 3 — 600 points
Diagnostic Testing
A screening test is evaluated in 1,000 patients. The gold standard identifies 300 patients with the disease. The new test has a sensitivity of 80% and a specificity of 90%.
How many false-negative and false-positive results are expected, respectively?
A. 30 false negatives; 60 false positives
B. 60 false negatives; 70 false positives
C. 60 false negatives; 90 false positives
D. 240 false negatives; 630 false positives
E. 70 false negatives; 60 false positives
Correct answer: B. 60 false negatives; 70 false positives
400
Mitochondria & Mitochondrial Genetics
Two siblings inherit the same maternally transmitted mitochondrial DNA mutation, but one develops severe disease while the other has mild symptoms. Which concept best explains how differing mutant mitochondrial DNA proportions contribute to their different presentations?
A. Genomic imprinting
B. Complete dominance
C. Mitochondrial threshold effect
D. X-linked recessive inheritance
E. Codominance of nuclear alleles
Correct answer: C. Mitochondrial threshold effect
Heteroplasmy means that mutant and normal mtDNA coexist. The mitochondrial threshold hypothesis explains why differing mutation burdens can produce different disease severity. The mitochondrial bottleneck can contribute to different mutant proportions among siblings.
Concept Tested: Heteroplasmy and mitochondrial threshold
400
Enzymes, Regulation & Bioenergetics
An enzyme inhibitor binds only after substrate has formed an enzyme–substrate complex. Laboratory measurements show both a decreased apparent Km and decreased Vmax. Which inhibition mechanism best fits these findings?
A. Competitive inhibition
B. Pure noncompetitive inhibition
C. Uncompetitive inhibition
D. Reversible competitive activation
E. Substrate saturation
Correct answer: C. Uncompetitive inhibition
Uncompetitive inhibitors bind only the enzyme–substrate complex and decrease both apparent Km and Vmax. Competitive inhibition increases Km without changing Vmax; pure noncompetitive inhibition decreases Vmax without changing Km.
Concept Tested: Uncompetitive enzyme inhibition
400
A drug selectively blocks nicotinic neuronal (Nn) receptors in autonomic ganglia without affecting muscarinic or adrenergic receptors. Which effect best describes the consequence of this blockade?
A. Selective inhibition of parasympathetic signaling only
B. Selective inhibition of sympathetic signaling only
C. Impaired transmission through both sympathetic and parasympathetic ganglia
D. Direct blockade of acetylcholine receptors at skeletal muscle neuromuscular junctions
E. Increased norepinephrine release from all sympathetic postganglionic neurons
Correct answer: C. Impaired transmission through both sympathetic and parasympathetic ganglia
Both sympathetic and parasympathetic preganglionic neurons release ACh onto Nn receptors in autonomic ganglia. Blocking these receptors impairs ganglionic transmission in both divisions. Skeletal muscle uses Nm receptors instead.
400
An obstruction prevents cerebrospinal fluid from flowing out of the right lateral ventricle into the third ventricle. Which ventricular structure would be expected to enlarge most directly upstream of the obstruction?
A. Fourth ventricle
B. Third ventricle
C. Right lateral ventricle
D. Cerebral aqueduct
E. Central canal of spinal cord
Correct answer: C. Right lateral ventricle
An obstruction causes CSF to accumulate upstream. With outflow from the right lateral ventricle blocked, that ventricle enlarges. Your CNS lecture emphasized ventricular enlargement due to CSF blockage.
400
A screening test uses a numerical biomarker to identify patients with a disease. Patients with values above the cutoff are considered positive. Researchers lower the cutoff from 140 to 100 to reduce the number of missed cases.
Which change is most likely to occur?
A. Sensitivity decreases; specificity increases.
B. Sensitivity increases; specificity increases.
C. Sensitivity decreases; specificity decreases.
D. Sensitivity increases; specificity decreases.
E. Sensitivity and specificity remain unchanged.
Correct answer: D. Sensitivity increases; specificity decreases
Lowering the cutoff catches more true positives and reduces false negatives, but also increases false positives.Raising the cutoff has the opposite effect: higher specificity, lower sensitivity.
500
Microtubules, Intermediate Filaments & Microfilaments
A child develops recurrent skin blisters within the basal layer of the epidermis, above the basal lamina. A defect in which cytoskeletal component best explains this finding?
A. Actin microfilaments
B. Tubulin microtubules
C. Keratin intermediate filaments
D. Collagen fibers
E. Elastin fibers
Correct answer: C. Keratin intermediate filaments
Epidermolysis bullosa simplex involves defective keratin intermediate filaments in basal epidermal cells. Your cytoskeleton OLM emphasized the location of blister formation and its relationship to keratin.
Concept Tested: Keratin and epidermolysis bullosa simplex
500
Signal Transduction
A ligand activates a G protein–coupled receptor, causing the Gα subunit to exchange GDP for GTP. The activated subunit stimulates adenylyl cyclase, ultimately promoting phosphorylation responses and transcriptional regulation through CREB. Which signaling sequence best describes this pathway?
A. Gq → phospholipase C → IP₃ → intracellular Ca²⁺
B. Gi → adenylyl cyclase inhibition → decreased cAMP
C. Gs → adenylyl cyclase → cAMP → PKA → CREB
D. Receptor tyrosine kinase → direct nuclear import of ligand
E. Ionotropic receptor → direct opening of a chloride channel
Correct answer: C. Gs → adenylyl cyclase → cAMP → PKA → CREB
Gs activates adenylyl cyclase, increasing cAMP. cAMP activates PKA, which can phosphorylate downstream targets involved in CREB-mediated transcription. Your Slusarz signal-transduction Q&A emphasized Gs, cAMP, PKA, and CREB.
Concept Tested: Gs → cAMP → PKA → CREB pathway
500
A researcher administers a drug that activates M2 muscarinic receptors in the sinoatrial node. The drug increases potassium conductance and decreases intracellular cAMP. Which electrical change best explains the resulting decrease in heart rate?
A. Increased slope of phase 4 depolarization
B. Decreased slope of phase 4 depolarization
C. Increased sodium conductance producing faster spontaneous firing
D. Blockade of potassium efflux, producing sustained depolarization
E. Increased calcium-dependent neurotransmitter release from sympathetic terminals
Correct answer: B. Decreased slope of phase 4 depolarization
M2 receptors decrease cAMP and increase K⁺ conductance, slowing spontaneous phase 4 depolarization in pacemaker cells. Threshold is reached less frequently, reducing heart rate.
500
A patient sustains a fracture involving the foramen ovale at the base of the skull. Which cranial nerve division is most likely affected as it exits the cranial cavity?
A. Ophthalmic division of trigeminal nerve (V1)
B. Maxillary division of trigeminal nerve (V2)
C. Mandibular division of trigeminal nerve (V3)
D. Facial nerve (VII)
E. Glossopharyngeal nerve (IX)
Correct answer: C. Mandibular division of trigeminal nerve (V3)
The mandibular division (V3) passes through the foramen ovale. V1 passes through the superior orbital fissure, V2 through foramen rotundum, and CN IX through the jugular foramen.
500
A diagnostic test has a sensitivity of 90% and specificity of 95%. It is used to screen 2,000 individuals in a population where disease prevalence is 5%.
What is the approximate positive predictive value (PPV) of the test?
A. 32%
B. 49%
C. 65%
D. 90%
E. 95%
Correct answer: B. Approximately 49%
Diseased = 2,000 × 0.05 = 100.
Nondiseased = 1,900.
TP = 100 × 0.90 = 90.
FP = 1,900 × 0.05 = 95.
Even with high sensitivity and specificity, PPV can be relatively low when disease prevalence is low.