De novo synthesis of fatty acids (Palmitic acid) MCQs With Answer

De novo synthesis of fatty acids (Palmitic acid) MCQs With Answer

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Understanding de novo synthesis of fatty acids, especially palmitic acid, is essential for B. Pharm students studying lipid biochemistry and drug action. This concise guide covers key concepts: cytosolic pathway from citrate to acetyl‑CoA, ATP‑citrate lyase, acetyl‑CoA carboxylase (biotin‑dependent) forming malonyl‑CoA, and the fatty acid synthase (FAS) complex that iteratively builds palmitate (C16:0) using NADPH. You’ll learn stoichiometry (8 acetyl‑CoA, 7 ATP, 14 NADPH), regulation by citrate, insulin and AMPK, and links to beta‑oxidation via malonyl‑CoA’s inhibition of CPT‑1. Clinical and pharmacological relevance, including FAS/ACC inhibitors and cancer metabolism, are highlighted. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which organelle supplies citrate for cytosolic de novo fatty acid synthesis?

  • Mitochondrion
  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosome

Correct Answer: Mitochondrion

Q2. The enzyme that converts citrate to acetyl‑CoA and oxaloacetate in the cytosol is:

  • ATP‑citrate lyase
  • Acetyl‑CoA carboxylase
  • Citrate synthase
  • Malate dehydrogenase

Correct Answer: ATP‑citrate lyase

Q3. Acetyl‑CoA carboxylase (ACC) catalyzes the formation of which key intermediate for fatty acid synthesis?

  • Acetoacetyl‑CoA
  • Malonyl‑CoA
  • Palmitoyl‑CoA
  • Citrate

Correct Answer: Malonyl‑CoA

Q4. The prosthetic group required by acetyl‑CoA carboxylase for carboxylation reactions is derived from which vitamin?

  • Biotin (vitamin B7)
  • Pantothenic acid (vitamin B5)
  • Riboflavin (vitamin B2)
  • Niacin (vitamin B3)

Correct Answer: Biotin (vitamin B7)

Q5. How many acetyl‑CoA molecules are directly incorporated into one molecule of palmitate (C16:0)?

  • 7 acetyl‑CoA
  • 8 acetyl‑CoA
  • 16 acetyl‑CoA
  • 4 acetyl‑CoA

Correct Answer: 8 acetyl‑CoA

Q6. The fatty acid synthase (FAS) complex in mammals is best described as:

  • A multienzyme complex encoded by multiple separate genes (Type II)
  • A large homodimeric multifunctional polypeptide (Type I)
  • A monofunctional enzyme working independently
  • An enzyme localized exclusively in mitochondria

Correct Answer: A large homodimeric multifunctional polypeptide (Type I)

Q7. Which carrier protein transfers acyl intermediates during fatty acid synthesis?

  • Coenzyme A only
  • Acyl carrier protein (ACP)
  • Albumin
  • Fatty acid binding protein (FABP)

Correct Answer: Acyl carrier protein (ACP)

Q8. The 4′-phosphopantetheine prosthetic group of ACP is derived from which vitamin?

  • Biotin
  • Pantothenic acid (vitamin B5)
  • Thiamine (vitamin B1)
  • Folate (vitamin B9)

Correct Answer: Pantothenic acid (vitamin B5)

Q9. Which cofactor provides reducing equivalents for the two reduction steps in each FAS cycle?

  • NADH
  • NADPH
  • FADH2
  • ATP

Correct Answer: NADPH

Q10. Approximately how many NADPH molecules are required to synthesize one molecule of palmitate?

  • 8 NADPH
  • 14 NADPH
  • 7 NADPH
  • 16 NADPH

Correct Answer: 14 NADPH

Q11. Which two pathways are the major cytosolic sources of NADPH for fatty acid synthesis?

  • Glycolysis and TCA cycle
  • Pentose phosphate pathway and malic enzyme
  • Electron transport chain and beta‑oxidation
  • Urea cycle and gluconeogenesis

Correct Answer: Pentose phosphate pathway and malic enzyme

Q12. The first condensation reaction in FAS uses which two substrates?

  • Two acetyl‑CoA molecules
  • Acetyl‑ACP and malonyl‑ACP
  • Malonyl‑CoA and palmitoyl‑CoA
  • Acetoacetyl‑ACP and NADPH

Correct Answer: Acetyl‑ACP and malonyl‑ACP

Q13. Which enzymatic activity of FAS catalyzes the release of palmitate from the enzyme complex?

  • Thioesterase
  • Dehydratase
  • Ketoreductase
  • Acyltransferase

Correct Answer: Thioesterase

Q14. Which molecule allosterically activates acetyl‑CoA carboxylase (ACC)?

  • Palmitoyl‑CoA
  • Citrate
  • AMP
  • Glucagon

Correct Answer: Citrate

Q15. AMP‑activated protein kinase (AMPK) affects ACC by:

  • Phosphorylating and activating ACC
  • Dephosphorylating and activating ACC
  • Phosphorylating and inhibiting ACC
  • Increasing ACC gene transcription acutely

Correct Answer: Phosphorylating and inhibiting ACC

Q16. Malonyl‑CoA inhibits which mitochondrial transporter to coordinate synthesis and oxidation?

  • Carnitine palmitoyltransferase‑1 (CPT‑1)
  • ATP synthase
  • Mitochondrial pyruvate carrier
  • Acyl‑CoA dehydrogenase

Correct Answer: Carnitine palmitoyltransferase‑1 (CPT‑1)

Q17. Which hormone signaling promotes dephosphorylation and activation of ACC, favoring fatty acid synthesis?

  • Glucagon
  • Adrenaline
  • Insulin
  • Cortisol

Correct Answer: Insulin

Q18. The stoichiometric ATP requirement to synthesize palmitate (for malonyl‑CoA formation) is:

  • 14 ATP
  • 8 ATP
  • 7 ATP
  • 0 ATP

Correct Answer: 7 ATP

Q19. Which enzyme in the cytosol regenerates NADPH while converting malate to pyruvate?

  • Malate dehydrogenase (mitochondrial)
  • Malic enzyme (ME1)
  • Pyruvate carboxylase
  • Citrate lyase

Correct Answer: Malic enzyme (ME1)

Q20. In mammals, fatty acid synthase deficiency would most directly decrease synthesis of which fatty acid?

  • Linoleic acid (18:2, n‑6)
  • Palmitic acid (16:0)
  • Oleic acid (18:1)** only
  • Arachidonic acid (20:4, n‑6)

Correct Answer: Palmitic acid (16:0)

Q21. Which of the following statements about malonyl‑CoA is true?

  • It directly supplies two‑carbon units and its decarboxylation drives condensation
  • It is synthesized from palmitate by ACC
  • It is exclusively produced in mitochondria
  • It is a reducing cofactor for FAS

Correct Answer: It directly supplies two‑carbon units and its decarboxylation drives condensation

Q22. Which enzyme is the rate‑limiting step for de novo fatty acid synthesis?

  • Fatty acid synthase (FAS)
  • ATP‑citrate lyase
  • Acetyl‑CoA carboxylase (ACC)
  • Citrate synthase

Correct Answer: Acetyl‑CoA carboxylase (ACC)

Q23. Which statement distinguishes FAS Type I (mammalian) from Type II (bacterial)?

  • Type I is a single multifunctional polypeptide; Type II uses separate enzymes
  • Type I uses NADH; Type II uses NADPH
  • Type I synthesizes only odd‑chain fatty acids; Type II makes even‑chain
  • Type I is localized to mitochondria; Type II is cytosolic

Correct Answer: Type I is a single multifunctional polypeptide; Type II uses separate enzymes

Q24. Which desaturase is responsible for introducing the first double bond at the Δ9 position of stearoyl‑CoA?

  • Delta‑6 desaturase
  • Stearoyl‑CoA desaturase (Δ9)
  • Delta‑12 desaturase
  • Acyl‑CoA oxidase

Correct Answer: Stearoyl‑CoA desaturase (Δ9)

Q25. Elongation of palmitate to stearate (C18:0) primarily occurs in which cellular compartment?

  • Mitochondrial matrix
  • Endoplasmic reticulum (ER)
  • Peroxisome only
  • Nucleus

Correct Answer: Endoplasmic reticulum (ER)

Q26. Which molecules are direct products when ACC converts acetyl‑CoA to malonyl‑CoA?

  • Malonyl‑CoA and ADP
  • Malonyl‑CoA and Pi
  • Malonyl‑CoA, ADP and Pi via ATP consumption
  • Malonyl‑CoA and CO2 only

Correct Answer: Malonyl‑CoA, ADP and Pi via ATP consumption

Q27. Which of the following inhibits acetyl‑CoA carboxylase activity?

  • Citrate
  • Insulin signaling
  • Palmitoyl‑CoA
  • Active protein phosphatase

Correct Answer: Palmitoyl‑CoA

Q28. Cancer cells often show upregulated fatty acid synthase (FAS). Pharmacologically targeting FAS is considered because:

  • FAS inhibition increases cholesterol synthesis exclusively
  • Rapidly proliferating cells require de novo lipids for membranes
  • FAS is the primary source of ATP in tumors
  • FAS inhibitors boost fatty acid oxidation directly

Correct Answer: Rapidly proliferating cells require de novo lipids for membranes

Q29. Which enzyme supplies cytosolic acetyl‑CoA from citrate and is often upregulated in lipogenic tissues?

  • Citrate synthase
  • ATP‑citrate lyase (ACL)
  • Acetyl‑CoA synthetase
  • Pyruvate dehydrogenase

Correct Answer: ATP‑citrate lyase (ACL)

Q30. During one FAS cycle (2‑carbon elongation), which sequence of reactions occurs?

  • Condensation → dehydration → two reductions
  • Condensation → reduction → dehydration → reduction
  • Reduction → condensation → dehydration → reduction
  • Dehydration → reduction → condensation → reduction

Correct Answer: Condensation → reduction → dehydration → reduction

Q31. Which of the following is NOT an essential fatty acid (must be obtained from diet)?

  • Linoleic acid (18:2 n‑6)
  • Alpha‑linolenic acid (18:3 n‑3)
  • Palmitic acid (16:0)
  • None of the above

Correct Answer: Palmitic acid (16:0)

Q32. Which mitochondrial process is directly limited by increased malonyl‑CoA levels?

  • Gluconeogenesis
  • Beta‑oxidation of fatty acids
  • TCA cycle flux
  • Urea cycle

Correct Answer: Beta‑oxidation of fatty acids

Q33. Which domain of FAS is responsible for reducing β‑keto intermediates using NADPH?

  • Ketoreductase (KR)
  • Dehydratase (DH)
  • Thioesterase (TE)
  • Condensing enzyme (KS)

Correct Answer: Ketoreductase (KR)

Q34. Which experimental tracer is commonly used to measure de novo lipogenesis in cells?

  • 14C‑acetate or 3H‑water incorporation into lipids
  • 32P‑ATP incorporation into DNA
  • 14C‑glucose oxidation to CO2 exclusively
  • Urine ketone measurement

Correct Answer: 14C‑acetate or 3H‑water incorporation into lipids

Q35. In bacteria, fatty acid synthesis inhibitors such as triclosan target which enzyme system?

  • Type I FAS complex
  • Type II enoyl‑ACP reductase (FabI)
  • Mammalian ACC1
  • Stearoyl‑CoA desaturase

Correct Answer: Type II enoyl‑ACP reductase (FabI)

Q36. Which factor would most increase hepatic de novo lipogenesis?

  • High AMP and fasting state
  • High carbohydrate diet and hyperinsulinemia
  • Prolonged exercise and low insulin
  • Administration of AMPK activators

Correct Answer: High carbohydrate diet and hyperinsulinemia

Q37. The decarboxylation of malonyl‑ACP during the condensation step primarily serves to:

  • Provide reducing equivalents
  • Drive the Claisen condensation thermodynamically
  • Generate NADPH
  • Release CO2 for biosynthesis

Correct Answer: Drive the Claisen condensation thermodynamically

Q38. Which isoform of ACC is most directly linked to regulation of fatty acid synthesis in lipogenic tissues?

  • ACC1 (cytosolic)
  • ACC2 (mitochondrial membrane‑associated)
  • ACC3 (peroxisomal)
  • ACC4 (nuclear)

Correct Answer: ACC1 (cytosolic)

Q39. Which enzyme introduces double bonds into fatty acids and requires O2 and cytochrome b5?

  • Fatty acid elongase (ELOVL)
  • Desaturase (e.g., stearoyl‑CoA desaturase)
  • Acyl‑CoA oxidase
  • Acyl‑protein thioesterase

Correct Answer: Desaturase (e.g., stearoyl‑CoA desaturase)

Q40. Which substrate is the primer bound to the KS (ketoacyl synthase) active site at initiation of palmitate synthesis?

  • Malonyl‑ACP
  • Acetyl‑CoA (as acetyl‑KS or acetyl‑transfer)
  • Palmitoyl‑ACP
  • Acetoacetyl‑CoA

Correct Answer: Acetyl‑CoA (as acetyl‑KS or acetyl‑transfer)

Q41. A mutation that prevents ACP phosphopantetheinylation would most directly impair:

  • NADPH production
  • Acyl group tethering to ACP and chain elongation
  • Malonyl‑CoA synthesis by ACC
  • Carnitine shuttle function

Correct Answer: Acyl group tethering to ACP and chain elongation

Q42. Which enzyme activity is required to convert cytosolic oxaloacetate back to pyruvate while generating NADPH?

  • Malate dehydrogenase (cytosolic) only
  • Malic enzyme converting malate to pyruvate (ME1)
  • Pyruvate carboxylase
  • Isocitrate dehydrogenase (mitochondrial)

Correct Answer: Malic enzyme converting malate to pyruvate (ME1)

Q43. Which lipid product would you expect to decrease first after pharmacologic inhibition of ATP‑citrate lyase in the liver?

  • Cholesterol only
  • Cytosolic acetyl‑CoA derived lipids including fatty acids and cholesterol
  • Ketone bodies exclusively
  • Triglycerides in adipose only

Correct Answer: Cytosolic acetyl‑CoA derived lipids including fatty acids and cholesterol

Q44. Which of the following best describes the thermodynamic contribution of malonyl‑CoA decarboxylation to fatty acid elongation?

  • Decarboxylation is endergonic and consumes ATP
  • Decarboxylation releases CO2 and makes condensation exergonic
  • Decarboxylation generates NADPH for reduction
  • Decarboxylation removes a two‑carbon unit as CO2

Correct Answer: Decarboxylation releases CO2 and makes condensation exergonic

Q45. Which technique would best identify changes in expression of FAS protein in liver tissue?

  • RT‑PCR for mRNA only
  • Western blot for FAS protein
  • GC‑MS fatty acid profiling only
  • Enzyme histochemistry for ACC only

Correct Answer: Western blot for FAS protein

Q46. Which statement about palmitic acid is correct?

  • It is an essential polyunsaturated fatty acid
  • It is a 16‑carbon saturated fatty acid produced by FAS
  • It cannot be elongated or desaturated in cells
  • It directly inhibits ACC when present

Correct Answer: It is a 16‑carbon saturated fatty acid produced by FAS

Q47. In mammals, malonyl‑CoA for cytosolic fatty acid synthesis is synthesized by which cellular enzyme using ATP and bicarbonate?

  • Acyl‑CoA synthetase
  • Acetyl‑CoA carboxylase (ACC)
  • Pyruvate carboxylase
  • Citrate lyase

Correct Answer: Acetyl‑CoA carboxylase (ACC)

Q48. Which regulatory change would you expect after prolonged fasting to reduce hepatic lipogenesis?

  • Increased insulin and ACC activation
  • AMPK activation leading to ACC phosphorylation and inhibition
  • Upregulation of ATP‑citrate lyase activity
  • Increased citrate export from mitochondria

Correct Answer: AMPK activation leading to ACC phosphorylation and inhibition

Q49. Which fatty acid modification occurs in the endoplasmic reticulum and requires malonyl‑CoA and NADPH?

  • Fatty acid β‑oxidation
  • Elongation of long‑chain fatty acids (ELOVL enzymes)
  • De novo synthesis initiation
  • Glycerol backbone synthesis

Correct Answer: Elongation of long‑chain fatty acids (ELOVL enzymes)

Q50. Which best summarizes the overall stoichiometry for palmitate synthesis from acetyl‑CoA, ATP and NADPH?

  • 8 acetyl‑CoA + 7 ATP + 14 NADPH → palmitate + byproducts
  • 16 acetyl‑CoA + 14 ATP + 7 NADPH → palmitate
  • 4 acetyl‑CoA + 7 ATP + 14 NADPH → palmitate
  • 8 acetyl‑CoA + 14 ATP + 7 NADPH → palmitate

Correct Answer: 8 acetyl‑CoA + 7 ATP + 14 NADPH → palmitate + byproducts

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