Introduction: The β-oxidation of saturated fatty acids, exemplified by palmitic acid (C16), is a central pathway in fatty acid metabolism that converts long-chain acyl-CoAs into acetyl-CoA, generating FADH2 and NADH for ATP production. For B. Pharm students, mastering the steps—activation by acyl-CoA synthetase, mitochondrial transport via the carnitine shuttle, the four-step dehydrogenation-hydration-dehydrogenation-thiolysis cycle, and regulation by malonyl-CoA—is essential for understanding energy yield, clinical disorders (e.g., MCAD deficiency), and drug interactions. This concise review focuses on mechanisms, enzymes, cofactors, energy calculations, and clinical relevance to aid exam preparation. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which cellular location is the primary site for β-oxidation of palmitic acid?
- Mitochondrial matrix
- Cytosol
- Smooth endoplasmic reticulum
- Golgi apparatus
Correct Answer: Mitochondrial matrix
Q2. Which enzyme catalyzes the activation of palmitic acid to palmitoyl‑CoA?
- Acyl-CoA synthetase (fatty acyl‑CoA ligase)
- Carnitine palmitoyltransferase I (CPT-I)
- Acyl-CoA dehydrogenase
- β‑ketothiolase
Correct Answer: Acyl-CoA synthetase (fatty acyl‑CoA ligase)
Q3. What is the energetic cost of activating palmitic acid to palmitoyl‑CoA?
- 1 ATP equivalent
- 2 ATP equivalents (ATP → AMP + PPi)
- No ATP required
- 3 ATP equivalents
Correct Answer: 2 ATP equivalents (ATP → AMP + PPi)
Q4. Which molecule inhibits carnitine palmitoyltransferase I (CPT‑I) and thus regulates β‑oxidation?
- Malonyl‑CoA
- Acetyl‑CoA
- Free fatty acids
- Carnitine
Correct Answer: Malonyl‑CoA
Q5. How many β‑oxidation cycles are required to fully oxidize palmitic acid (C16) to acetyl‑CoA?
- 6 cycles
- 7 cycles
- 8 cycles
- 16 cycles
Correct Answer: 7 cycles
Q6. How many acetyl‑CoA molecules are produced by complete β‑oxidation of palmitic acid?
- 6 acetyl‑CoA
- 7 acetyl‑CoA
- 8 acetyl‑CoA
- 16 acetyl‑CoA
Correct Answer: 8 acetyl‑CoA
Q7. Each β‑oxidation cycle (except the final cleavage) directly generates which reduced cofactors?
- 1 NADPH and 1 FADH2
- 1 NADH and 1 FADH2
- 2 NADH
- 2 FADH2
Correct Answer: 1 NADH and 1 FADH2
Q8. What is the correct order of enzymes in one round of mitochondrial β‑oxidation?
- Enoyl‑CoA hydratase → acyl‑CoA dehydrogenase → 3‑hydroxyacyl‑CoA dehydrogenase → thiolase
- Acyl‑CoA dehydrogenase → enoyl‑CoA hydratase → 3‑hydroxyacyl‑CoA dehydrogenase → β‑ketothiolase
- Thiolase → acyl‑CoA dehydrogenase → enoyl‑CoA hydratase → 3‑hydroxyacyl‑CoA dehydrogenase
- 3‑hydroxyacyl‑CoA dehydrogenase → enoyl‑CoA hydratase → acyl‑CoA dehydrogenase → thiolase
Correct Answer: Acyl‑CoA dehydrogenase → enoyl‑CoA hydratase → 3‑hydroxyacyl‑CoA dehydrogenase → β‑ketothiolase
Q9. Which cofactor is directly reduced by acyl‑CoA dehydrogenase during the first step of β‑oxidation?
- NAD+
- FAD
- NADP+
- Coenzyme Q
Correct Answer: FAD
Q10. The 3‑hydroxyacyl‑CoA dehydrogenase step uses which cofactor?
- NADP+
- FAD
- NAD+
- Biotin
Correct Answer: NAD+
Q11. What is the name of the enzyme that cleaves 3‑ketoacyl‑CoA to yield acetyl‑CoA and a shortened acyl‑CoA?
- Thiolase (β‑ketothiolase)
- Acyl‑CoA synthetase
- Enoyl‑CoA isomerase
- Carboxylase
Correct Answer: Thiolase (β‑ketothiolase)
Q12. Using modern P/O ratios (NADH = 2.5, FADH2 = 1.5), what is the theoretical net ATP yield from complete oxidation of palmitate (after subtracting activation cost)?
- 96 ATP
- 106 ATP
- 120 ATP
- 80 ATP
Correct Answer: 106 ATP
Q13. Which metabolic intermediate produced during fatty acid synthesis acts as a physiological inhibitor of β‑oxidation?
- Citrate
- Malonyl‑CoA
- Oxaloacetate
- Succinyl‑CoA
Correct Answer: Malonyl‑CoA
Q14. Peroxisomal β‑oxidation is particularly important for shortening which type of fatty acids?
- Short‑chain fatty acids (C4–C8)
- Medium‑chain fatty acids (C8–C12)
- Very‑long‑chain fatty acids (≥ C20)
- Unsaturated fatty acids only
Correct Answer: Very‑long‑chain fatty acids (≥ C20)
Q15. Oxidation of odd‑chain fatty acids yields which three‑carbon product that is further metabolized?
- Lactyl‑CoA
- Propionyl‑CoA
- Butyryl‑CoA
- Formyl‑CoA
Correct Answer: Propionyl‑CoA
Q16. Conversion of propionyl‑CoA to succinyl‑CoA requires which vitamin as a cofactor for methylmalonyl‑CoA mutase?
- Vitamin B6 (pyridoxine)
- Vitamin B12 (cobalamin)
- Biotin (vitamin B7)
- Vitamin K
Correct Answer: Vitamin B12 (cobalamin)
Q17. Which enzyme converts acyl‑carnitine back to acyl‑CoA inside the mitochondrial matrix?
- Carnitine palmitoyltransferase I (CPT‑I)
- Carnitine palmitoyltransferase II (CPT‑II)
- Carnitine acetyltransferase
- Carnitine translocase
Correct Answer: Carnitine palmitoyltransferase II (CPT‑II)
Q18. Which hormonal state stimulates β‑oxidation in liver and muscle?
- High insulin, fed state
- High glucagon, fasting state
- High thyroxine only
- High insulin and high glucagon simultaneously
Correct Answer: High glucagon, fasting state
Q19. Oxidation of unsaturated fatty acids requires additional enzymes. Which of the following participates in handling cis‑double bonds?
- Enoyl‑CoA isomerase
- Acyl‑CoA carboxylase
- Acyl‑CoA synthetase
- Thiokinase
Correct Answer: Enoyl‑CoA isomerase
Q20. Fatty acid activation requires which of the following cofactors?
- Coenzyme A (CoA) and ATP
- Thiamine pyrophosphate and NAD+
- Biotin and CO2
- FAD and FMN
Correct Answer: Coenzyme A (CoA) and ATP
Q21. During the first dehydrogenation step, which immediate product is formed from acyl‑CoA?
- cis‑Δ3‑enoyl‑CoA
- trans‑Δ2‑enoyl‑CoA
- L‑3‑hydroxyacyl‑CoA
- β‑ketoacyl‑CoA
Correct Answer: trans‑Δ2‑enoyl‑CoA
Q22. Which shuttle transports fatty acyl groups across the inner mitochondrial membrane?
- Malate–aspartate shuttle
- Carnitine shuttle
- Glycerol‑3‑phosphate shuttle
- Alpha‑ketoglutarate shuttle
Correct Answer: Carnitine shuttle
Q23. A deficiency of carnitine transporter or severe carnitine deficiency primarily causes which metabolic consequence?
- Excess ketone body formation
- Impaired long‑chain fatty acid oxidation and muscle weakness
- Enhanced β‑oxidation and hyperketonemia
- Decreased fatty acid synthesis only
Correct Answer: Impaired long‑chain fatty acid oxidation and muscle weakness
Q24. Which organ is the main site for ketone body synthesis from excess acetyl‑CoA generated by β‑oxidation?
- Muscle
- Liver
- Brain
- Kidney cortex
Correct Answer: Liver
Q25. How many NADH and FADH2 molecules are produced during the β‑oxidation cycles (not including TCA) of palmitate?
- 8 NADH and 8 FADH2
- 7 NADH and 7 FADH2
- 16 NADH and 16 FADH2
- 0 NADH and 0 FADH2
Correct Answer: 7 NADH and 7 FADH2
Q26. The hydration step of β‑oxidation converts trans‑Δ2‑enoyl‑CoA into which intermediate?
- D‑3‑hydroxyacyl‑CoA
- L‑3‑hydroxyacyl‑CoA
- β‑ketoacyl‑CoA
- Acyl‑Carnitine
Correct Answer: L‑3‑hydroxyacyl‑CoA
Q27. The stereospecificity of the hydration step yields which stereoisomer that is substrate for the dehydrogenase?
- D‑3‑hydroxyacyl‑CoA
- L‑3‑hydroxyacyl‑CoA
- R‑2‑hydroxyacyl‑CoA
- S‑2‑hydroxyacyl‑CoA
Correct Answer: L‑3‑hydroxyacyl‑CoA
Q28. The complete β‑oxidation of even‑chain saturated fatty acids yields what end product(s) that enter the citric acid cycle?
- Pyruvate molecules
- Acetyl‑CoA molecules
- Lactate molecules
- Propionyl‑CoA molecules
Correct Answer: Acetyl‑CoA molecules
Q29. Which drug is known to inhibit CPT‑I and thereby block mitochondrial uptake of long‑chain fatty acids?
- Etomoxir
- Statins
- Metformin
- Niacin
Correct Answer: Etomoxir
Q30. How many carbon atoms are present in palmitic acid?
- 14 carbons
- 16 carbons
- 18 carbons
- 12 carbons
Correct Answer: 16 carbons
Q31. What is the rate‑limiting step of mitochondrial β‑oxidation of long‑chain fatty acids?
- Activation by acyl‑CoA synthetase
- Transport across the inner mitochondrial membrane via CPT‑I
- Thiolytic cleavage by thiolase
- Hydration by enoyl‑CoA hydratase
Correct Answer: Transport across the inner mitochondrial membrane via CPT‑I
Q32. Which intermediate is formed directly after the acyl‑CoA dehydrogenase reaction?
- β‑ketoacyl‑CoA
- L‑3‑hydroxyacyl‑CoA
- trans‑Δ2‑enoyl‑CoA
- Acetyl‑CoA
Correct Answer: trans‑Δ2‑enoyl‑CoA
Q33. The 3‑hydroxyacyl‑CoA dehydrogenase reaction oxidizes the hydroxyl group at C‑3 using which electron acceptor?
- NAD+
- FAD
- NADP+
- FMN
Correct Answer: NAD+
Q34. Electrons from acyl‑CoA dehydrogenase are transferred to the electron transport chain via which carrier?
- Cytochrome c
- ETF (electron transfer flavoprotein)
- Ubiquinone directly
- NADH dehydrogenase
Correct Answer: ETF (electron transfer flavoprotein)
Q35. Which cellular process produces H2O2 as a byproduct during fatty acid oxidation?
- Mitochondrial β‑oxidation
- Peroxisomal β‑oxidation (acyl‑CoA oxidase)
- β‑oxidation in cytosol
- Glycolysis
Correct Answer: Peroxisomal β‑oxidation (acyl‑CoA oxidase)
Q36. Deficiency of which vitamin can impair endogenous carnitine biosynthesis?
- Vitamin C (ascorbic acid)
- Vitamin D
- Vitamin K
- Vitamin B2 (riboflavin)
Correct Answer: Vitamin C (ascorbic acid)
Q37. Which enzyme requires biotin as a cofactor in the metabolism of propionyl‑CoA?
- Propionyl‑CoA carboxylase
- Methylmalonyl‑CoA mutase
- Pyruvate carboxylase
- Acyl‑CoA dehydrogenase
Correct Answer: Propionyl‑CoA carboxylase
Q38. Which enzyme catalyzes the thiolytic cleavage that shortens the fatty acyl chain by two carbons?
- Acyl‑CoA dehydrogenase
- β‑ketothiolase (thiolase)
- Enoyl‑CoA hydratase
- Acyl‑CoA carboxylase
Correct Answer: β‑ketothiolase (thiolase)
Q39. How much ATP is produced from the NADH and FADH2 generated during the seven β‑oxidation cycles of palmitate using P/O ratios NADH = 2.5 and FADH2 = 1.5?
- 14 ATP
- 28 ATP
- 7 ATP
- 56 ATP
Correct Answer: 28 ATP
Q40. How many ATP equivalents are generated in the citric acid cycle per acetyl‑CoA oxidized (conventional modern estimate)?
- 10 ATP per acetyl‑CoA
- 5 ATP per acetyl‑CoA
- 3 ATP per acetyl‑CoA
- 12 ATP per acetyl‑CoA
Correct Answer: 10 ATP per acetyl‑CoA
Q41. How many ATP are produced by the oxidation of 8 acetyl‑CoA molecules via the citric acid cycle (using 10 ATP per acetyl‑CoA)?
- 40 ATP
- 80 ATP
- 8 ATP
- 100 ATP
Correct Answer: 80 ATP
Q42. Deficiency of which enzyme causes medium‑chain acyl‑CoA dehydrogenase (MCAD) deficiency?
- Very‑long‑chain acyl‑CoA dehydrogenase (VLCAD)
- Medium‑chain acyl‑CoA dehydrogenase (MCAD)
- Short‑chain acyl‑CoA dehydrogenase (SCAD)
- Acyl‑CoA synthetase
Correct Answer: Medium‑chain acyl‑CoA dehydrogenase (MCAD)
Q43. Which acyl‑CoA dehydrogenase isoform primarily acts on medium‑chain fatty acids (C6–C12)?
- VLCAD (very‑long‑chain)
- MCAD (medium‑chain)
- LCAD (long‑chain)
- SCAD (short‑chain)
Correct Answer: MCAD (medium‑chain)
Q44. Which physiological condition suppresses fatty acid β‑oxidation in adipose tissue and liver?
- Fasting
- High insulin after a carbohydrate‑rich meal
- Exercise
- Starvation
Correct Answer: High insulin after a carbohydrate‑rich meal
Q45. During prolonged fasting, the brain adapts to use which compounds derived from hepatic β‑oxidation?
- Free fatty acids
- Ketone bodies (acetoacetate and β‑hydroxybutyrate)
- Lactate only
- Glycogen
Correct Answer: Ketone bodies (acetoacetate and β‑hydroxybutyrate)
Q46. The enzyme enoyl‑CoA isomerase plays a critical role in oxidation of which type of fatty acids?
- Saturated even‑chain fatty acids only
- Unsaturated fatty acids with cis‑double bonds at odd positions
- Branched‑chain amino acids
- Ketone bodies
Correct Answer: Unsaturated fatty acids with cis‑double bonds at odd positions
Q47. The 2,4‑dienoyl‑CoA reductase involved in unsaturated fatty acid oxidation uses which reducing cofactor?
- NADH
- NADPH
- FADH2
- FMNH2
Correct Answer: NADPH
Q48. Propionyl‑CoA generated from odd‑chain fatty acid oxidation is converted into which citric acid cycle intermediate?
- Oxaloacetate
- Succinyl‑CoA
- Alpha‑ketoglutarate
- Citrate
Correct Answer: Succinyl‑CoA
Q49. Carnitine required for the mitochondrial shuttle is obtained from which primary sources?
- Only synthesized in muscle
- Diet (e.g., red meat) and endogenous synthesis in liver and kidney
- Exclusively from gut microbiota
- Only produced in adipose tissue
Correct Answer: Diet (e.g., red meat) and endogenous synthesis in liver and kidney
Q50. A hallmark laboratory finding in a patient with defective mitochondrial β‑oxidation during fasting is:
- Elevated blood ketone bodies with hyperglycemia
- Hypoketotic hypoglycemia and elevated long‑chain acyl‑carnitines
- High blood lactate and increased ketone bodies
- Hypoglycemia with abundant urinary ketones
Correct Answer: Hypoketotic hypoglycemia and elevated long‑chain acyl‑carnitines
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.
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