Uncouplers of oxidative phosphorylation MCQs With Answer

Uncouplers of oxidative phosphorylation MCQs With Answer

Uncouplers of oxidative phosphorylation are agents that dissipate the proton gradient across the mitochondrial inner membrane, disrupting ATP synthesis and increasing heat production. This concise introduction explains mechanisms, chemical features (lipophilic weak acids, protonophores), physiological consequences (reduced ATP, increased O2 consumption), laboratory detection (membrane potential dyes, oxygen electrodes), examples (2,4‑DNP, FCCP, CCCP), and clinical/toxicological relevance (thermogenesis, DNP poisoning). It is tailored for B. Pharm students preparing for exams, linking biochemical principles to pharmacology and safety considerations. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary molecular action of classical chemical uncouplers of oxidative phosphorylation?

• Inhibition of complex I of the electron transport chain
• Shuttling protons across the inner mitochondrial membrane
• Direct inhibition of ATP synthase catalytic subunit
• Blocking ADP/ATP translocase

Correct Answer: Shuttling protons across the inner mitochondrial membrane

Q2. Which of the following is a classic uncoupler used in experimental bioenergetics?

• Oligomycin
• Rotenone
• 2,4‑Dinitrophenol (DNP)
• Cyanide

Correct Answer: 2,4‑Dinitrophenol (DNP)

Q3. How do uncouplers affect mitochondrial oxygen consumption in the presence of substrates and ADP?

• Decrease oxygen consumption
• No change in oxygen consumption
• Increase oxygen consumption to maximal rates
• Completely abolish oxygen consumption

Correct Answer: Increase oxygen consumption to maximal rates

Q4. What happens to ATP synthesis when an uncoupler is added to active mitochondria?

• ATP synthesis increases
• ATP synthesis decreases
• ATP synthesis is unaffected
• ATP synthesis is converted to GMP synthesis

Correct Answer: ATP synthesis decreases

Q5. Which statement correctly contrasts uncouplers with classic respiratory chain inhibitors?

• Uncouplers block electron flow; inhibitors dissipate the proton gradient
• Uncouplers dissipate the proton gradient; inhibitors block electron flow
• Both uncouplers and inhibitors block ATP synthase directly
• Both increase membrane potential

Correct Answer: Uncouplers dissipate the proton gradient; inhibitors block electron flow

Q6. Which property is characteristic of chemical uncouplers allowing them to cross membranes?

• Highly hydrophilic with multiple charges
• Lipophilic and exist as weak acids with delocalized charge
• Strong bases with permanent positive charge
• Large polar proteins

Correct Answer: Lipophilic and exist as weak acids with delocalized charge

Q7. What effect do uncouplers have on the proton motive force (Δp) across the inner mitochondrial membrane?

• Increase Δp
• Decrease Δp
• No effect on Δp
• Convert Δp into sodium motive force

Correct Answer: Decrease Δp

Q8. The chemiosmotic theory by Peter Mitchell explains the mechanism targeted by uncouplers. What does this theory propose?

• ATP is synthesized by substrate-level phosphorylation only
• Electron transport generates a proton gradient that drives ATP synthesis
• Mitochondria synthesize ATP by direct oxidation of ADP
• ATP is generated by passive diffusion of ATP across the membrane

Correct Answer: Electron transport generates a proton gradient that drives ATP synthesis

Q9. Which experimental observation indicates uncoupling when measuring mitochondrial respiration?

• Decreased state 4 respiration
• Increased respiratory control ratio (RCR)
• Increased state 4 (resting) respiration and decreased RCR
• Complete inhibition of oxygen consumption

Correct Answer: Increased state 4 (resting) respiration and decreased RCR

Q10. What is the effect of adding oligomycin (an ATP synthase inhibitor) followed by an uncoupler to isolated mitochondria?

• Oligomycin prevents uncoupler-induced increase in respiration
• Uncoupler reverses oligomycin’s inhibition by bypassing ATP synthase
• Oligomycin enhances uncoupler action
• No measurable effect because they act on the same site

Correct Answer: Uncoupler reverses oligomycin’s inhibition by bypassing ATP synthase

Q11. Which dye is commonly used to detect changes in mitochondrial membrane potential caused by uncouplers?

• Trichloroacetic acid
• JC‑1
• Bromophenol blue
• Ethidium bromide

Correct Answer: JC‑1

Q12. How does an uncoupler affect the ATP/ADP ratio in cells?

• Increases ATP/ADP ratio
• Decreases ATP/ADP ratio
• No change in ATP/ADP ratio
• Converts ATP to cAMP, altering ratio unpredictably

Correct Answer: Decreases ATP/ADP ratio

Q13. Which of the following is a protein uncoupler found in brown adipose tissue?

• UCP1 (thermogenin)
• ATP synthase β subunit
• Cytochrome c oxidase
• Creatine kinase

Correct Answer: UCP1 (thermogenin)

Q14. Activation of UCP1 leads primarily to:

• Increased ATP production
• Increased heat generation (non‑shivering thermogenesis)
• Decreased fatty acid oxidation
• Inhibition of electron transport

Correct Answer: Increased heat generation (non‑shivering thermogenesis)

Q15. Which statement best describes 2,4‑DNP’s historical and clinical significance?

• Safe weight‑loss drug still in use
• Used as an antibiotic with no metabolic effects
• Historically used for weight loss but banned due to fatal hyperthermia
• Primary treatment for mitochondrial diseases

Correct Answer: Historically used for weight loss but banned due to fatal hyperthermia

Q16. How do uncouplers influence reactive oxygen species (ROS) production by mitochondria?

• Always increase ROS production
• Always abolish ROS production
• May decrease ROS by lowering membrane potential, but effects vary with concentration
• Convert ROS into water directly

Correct Answer: May decrease ROS by lowering membrane potential, but effects vary with concentration

Q17. What is the expected change in NADH oxidation rate when a potent uncoupler is added to respiring mitochondria?

• NADH oxidation decreases
• NADH oxidation increases
• NADH oxidation is abolished completely
• NADH is converted to NADPH

Correct Answer: NADH oxidation increases

Q18. Why can uncouplers increase substrate oxidation without increasing ATP synthesis?

• They inhibit TCA cycle enzymes
• They dissipate the proton gradient so the ETC works faster but ATP synthase cannot harness the gradient
• They bind directly to ADP preventing phosphorylation
• They block mitochondrial ADP uptake

Correct Answer: They dissipate the proton gradient so the ETC works faster but ATP synthase cannot harness the gradient

Q19. What happens to the P/O ratio (ATP produced per oxygen atom reduced) in the presence of uncouplers?

• P/O ratio increases
• P/O ratio decreases
• P/O ratio remains unchanged
• P/O ratio becomes infinite

Correct Answer: P/O ratio decreases

Q20. Which structural feature often correlates with uncoupling potency in weak acid uncouplers?

• High hydrophilicity and low membrane partitioning
• Ability to delocalize negative charge and high lipophilicity
• Large polar head groups
• Permanent positive charge

Correct Answer: Ability to delocalize negative charge and high lipophilicity

Q21. Which of these substances is primarily an ATP synthase inhibitor rather than an uncoupler?

• Oligomycin
• CCCP
• FCCP
• DNP

Correct Answer: Oligomycin

Q22. If an electron transport inhibitor such as antimycin A is added, what is the effect of subsequently adding an uncoupler?

• Uncoupler increases respiration despite inhibition
• Uncoupler has no effect because electron flow is blocked
• Uncoupler restores electron transport past the block
• Uncoupler converts antimycin A into a benign compound

Correct Answer: Uncoupler has no effect because electron flow is blocked

Q23. Which laboratory measurement would most directly show that an uncoupler is active in mitochondria?

• Decrease in oxygen consumption rate
• Increase in mitochondrial membrane potential dye accumulation
• Increase in oxygen consumption and decrease in membrane potential
• Decrease in respiratory chain enzyme concentrations

Correct Answer: Increase in oxygen consumption and decrease in membrane potential

Q24. Salicylates at high concentrations can act as mild uncouplers. Which clinical phenomenon is consistent with this action?

• Hypothermia in salicylate overdose
• Metabolic acidosis and hyperthermia in overdose
• Hypoglycemia due to increased ATP production
• Complete inhibition of respiration causing decreased CO2

Correct Answer: Metabolic acidosis and hyperthermia in overdose

Q25. How does an uncoupler affect the ADP/O ratio during oxidative phosphorylation?

• ADP/O ratio increases
• ADP/O ratio decreases
• ADP/O ratio is unchanged
• ADP/O becomes negative

Correct Answer: ADP/O ratio decreases

Q26. Which term best describes chemical uncouplers that shuttle protons across membranes?

• Ionophores
• Protonophores
• Photosensitizers
• Hydrolases

Correct Answer: Protonophores

Q27. FCCP and CCCP are commonly used in research. What is their primary use?

• To inhibit glycolysis
• To chemically uncouple the mitochondrial membrane potential for maximal respiration assessment
• To stain DNA in fluorescence microscopy
• To inhibit lysosomal enzymes

Correct Answer: To chemically uncouple the mitochondrial membrane potential for maximal respiration assessment

Q28. Which pharmacological outcome is a direct risk of systemic administration of potent uncouplers?

• Excessive ATP accumulation
• Hyperthermia and fatal energy depletion
• Impaired oxygen delivery by hemoglobin
• Increased clotting tendency

Correct Answer: Hyperthermia and fatal energy depletion

Q29. How do free fatty acids regulate UCP1 activity in brown adipose tissue?

• Free fatty acids inhibit UCP1 by competitive binding
• Free fatty acids activate UCP1 leading to proton leak
• Free fatty acids have no effect on UCP1
• Free fatty acids degrade UCP1 protein

Correct Answer: Free fatty acids activate UCP1 leading to proton leak

Q30. Which experimental result indicates uncoupling when measuring ATP production and oxygen consumption simultaneously?

• ATP production rises proportionally with oxygen consumption
• Oxygen consumption rises while ATP production falls
• Both oxygen consumption and ATP production fall
• Neither oxygen consumption nor ATP production change

Correct Answer: Oxygen consumption rises while ATP production falls

Q31. Which of the following best explains why uncouplers cause heat production?

• They directly oxidize proteins to release heat
• Energy from substrate oxidation is released as heat instead of being conserved as ATP
• They increase muscle shivering only
• They induce fever by cytokine release only

Correct Answer: Energy from substrate oxidation is released as heat instead of being conserved as ATP

Q32. Which measurement would indicate a lowered mitochondrial membrane potential after uncoupler treatment?

• Increased uptake of rhodamine 123 dye
• Decreased uptake or depolarization‑sensitive dye signal
• Increased fluorescence of JC‑1 aggregates
• Increased ATP levels per mitochondrion

Correct Answer: Decreased uptake or depolarization‑sensitive dye signal

Q33. How does an uncoupler change the respiration control ratio (state 3/state 4)?

• RCR increases significantly
• RCR decreases significantly
• RCR remains the same
• RCR becomes undefined due to zero state 3 respiration

Correct Answer: RCR decreases significantly

Q34. Which cellular process becomes more active to compensate for ATP depletion caused by uncouplers?

• Protein biosynthesis increases to compensate
• Glycolysis increases to generate ATP anaerobically
• DNA replication increases
• Lipid biosynthesis increases markedly

Correct Answer: Glycolysis increases to generate ATP anaerobically

Q35. In bioenergetic assays, why are uncouplers used to determine maximal respiratory capacity?

• Uncouplers block respiration, revealing maximal inhibition
• They remove the feedback constraint of Δp, allowing maximal electron transport rate
• They stabilize ATP synthase so respiration is reproducible
• They increase mitochondrial mass

Correct Answer: They remove the feedback constraint of Δp, allowing maximal electron transport rate

Q36. Which structural class does CCCP belong to?

• Ribonucleotide analog
• N‑chlorinated peptide
• Uncoupling protonophore (lipophilic weak acid)
• Heavy metal chelator

Correct Answer: Uncoupling protonophore (lipophilic weak acid)

Q37. Which physiological tissue is specialized for uncoupling-mediated thermogenesis?

• White adipose tissue
• Brown adipose tissue
• Skeletal muscle only
• Liver only

Correct Answer: Brown adipose tissue

Q38. Which of the following is NOT an expected effect of a mitochondrial uncoupler?

• Increase in substrate oxidation rate
• Decrease in cellular ATP concentration
• Increase in mitochondrial membrane potential
• Elevated heat production

Correct Answer: Increase in mitochondrial membrane potential

Q39. Which laboratory technique can directly measure proton leak induced by uncouplers?

• Western blot for cytochrome c
• Seahorse extracellular flux analysis measuring oxygen consumption in presence of oligomycin
• PCR quantification of mitochondrial DNA
• ELISA for ATP synthase protein

Correct Answer: Seahorse extracellular flux analysis measuring oxygen consumption in presence of oligomycin

Q40. Why are uncouplers useful in studying mitochondrial efficiency and disease?

• They increase ATP yield making detection easier
• They reveal maximal respiratory capacity and defects in electron transport independent of ATP synthase
• They permanently fix mitochondria for microscopy
• They selectively kill mitochondria allowing study of cytosolic metabolism only

Correct Answer: They reveal maximal respiratory capacity and defects in electron transport independent of ATP synthase

Q41. Which factor reduces the effectiveness of a weak acid uncoupler to shuttle protons?

• High membrane solubility
• Strong ion pairing preventing membrane diffusion
• Delocalized negative charge
• Optimal pKa near physiological pH

Correct Answer: Strong ion pairing preventing membrane diffusion

Q42. Which clinical sign is most characteristic of DNP poisoning?

• Bradycardia without fever
• Marked hyperthermia with excessive sweating and metabolic acidosis
• Profound hypothermia and lethargy
• Isolated hypotension with no metabolic disturbance

Correct Answer: Marked hyperthermia with excessive sweating and metabolic acidosis

Q43. How does an uncoupler influence the redox state of electron carriers like cytochromes?

• Causes over‑reduction due to blocked electron flow
• Leads to more oxidized state due to increased electron flow to O2
• No effect on redox state
• Converts cytochromes into ATP directly

Correct Answer: Leads to more oxidized state due to increased electron flow to O2

Q44. In tissue exposed to an uncoupler, what is the likely effect on fuel utilization?

• Decreased fatty acid oxidation only
• Increased oxidation of carbohydrates and fats to meet energy demand
• Complete halt of substrate oxidation
• Sole reliance on amino acid catabolism

Correct Answer: Increased oxidation of carbohydrates and fats to meet energy demand

Q45. Which description correctly identifies FCCP’s effect in an intact cell assay measuring spare respiratory capacity?

• FCCP decreases spare respiratory capacity
• FCCP reveals maximal respiration, often increasing apparent spare capacity
• FCCP inhibits glycolysis, reducing capacity
• FCCP binds DNA and alters gene expression affecting respiration slowly

Correct Answer: FCCP reveals maximal respiration, often increasing apparent spare capacity

Q46. What is a major safety consideration for researchers when handling potent uncouplers like CCCP or FCCP?

• They are inert and require no precautions
• They are toxic lipophilic compounds; use PPE and avoid ingestion or skin contact
• They explode on contact with air
• They permanently label mitochondria fluorescently

Correct Answer: They are toxic lipophilic compounds; use PPE and avoid ingestion or skin contact

Q47. How does mitochondrial uncoupling affect cellular oxygen consumption under hypoxic conditions?

• Uncoupling is amplified under hypoxia leading to more oxygen consumption without benefit
• Under severe hypoxia, electron transport limits respiration so uncouplers have limited effect
• Uncouplers convert mitochondria to photosynthetic organelles in hypoxia
• Uncouplers supply oxygen to cells under hypoxia

Correct Answer: Under severe hypoxia, electron transport limits respiration so uncouplers have limited effect

Q48. Which molecular measurement would indicate increased uncoupling‑mediated thermogenesis in vivo?

• Decreased whole‑body oxygen consumption
• Elevated core body temperature and increased metabolic rate (O2 consumption)
• Decreased fatty acid oxidation markers
• Reduced heat production despite increased ATP

Correct Answer: Elevated core body temperature and increased metabolic rate (O2 consumption)

Q49. Which mitochondrial parameter is least likely to be directly affected by uncouplers?

• Proton gradient (Δp)
• ADP/ATP translocase expression level
• ATP synthesis rate
• Oxygen consumption rate

Correct Answer: ADP/ATP translocase expression level

Q50. For a new drug candidate suspected to be an uncoupler, which early assay would best screen for uncoupling activity?

• Measure increase in mitochondrial membrane potential using JC‑1
• Assess oxygen consumption increase in isolated mitochondria or permeabilized cells
• Measure DNA synthesis rate
• Quantify extracellular glucose concentration only

Correct Answer: Assess oxygen consumption increase in isolated mitochondria or permeabilized cells

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com