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Fatty Acid Synthesis

Tier 4 · #27 of 33 · lower yield · topic 3.10 — every high-yield fact from the book chapter, exam-ready.

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  1. Front
    In which subcellular compartment does de novo fatty acid synthesis occur?
    Back
    Cytosol
  2. Front
    What is the rate-limiting (committed) enzyme of fatty acid synthesis?
    Back
    Acetyl-CoA carboxylase 1 (ACC1)
  3. Front
    What is the immediate two-carbon raw material whose carbons end up in the fatty acid?
    Back
    Acetyl-CoA
  4. Front
    Why can't acetyl-CoA leave the mitochondria directly for fatty acid synthesis?
    Back
    The inner mitochondrial membrane is impermeable to acetyl-CoA
  5. Front
    In the citrate shuttle , in what disguised form does the acetyl group cross out of the mitochondria into the cytosol ?
    Back
    As citrate
  6. Front
    Which cytosolic enzyme cleaves citrate back into acetyl-CoA and oxaloacetate ?
    Back
    Citrate lyase (ATP-citrate lyase)
  7. Front
    How much ATP does the citrate lyase cleavage of citrate cost?
    Back
    1 ATP
  8. Front
    ACC1 carboxylates acetyl-CoA to form which three-carbon product?
    Back
    Malonyl-CoA
  9. Front
    Which cofactor serves as the CO2 carrier for the ACC1 reaction?
    Back
    Biotin
  10. Front
    Besides biotin , what high-energy molecule does the ACC1 reaction consume?
    Back
    ATP
  11. Front
    Which allosteric effector is a positive activator of ACC1 (and signals mitochondrial acetyl-CoA abundance)?
    Back
    Citrate
  12. Front
    Which end-product of fatty acid synthesis is a negative allosteric (feedback) inhibitor of ACC1 ?
    Back
    Palmitoyl-CoA
  13. Front
    Why does the cell convert acetyl-CoA to malonyl-CoA rather than elongate with acetyl-CoA directly?
    Back
    The added CO2 is released during condensation , and that decarboxylation energy drives the otherwise unfavorable condensation forward
  14. Front
    Which hormone turns fatty acid synthesis ON by activating a phosphatase that dephosphorylates ACC1 ?
    Back
    Insulin
  15. Front
    Which kinase phosphorylates and inactivates ACC1 in response to glucagon/adrenaline and low energy?
    Back
    AMPK (AMP-activated protein kinase)
  16. Front
    Cloze: For ACC1 , the phosphorylated form is ______ and the dephosphorylated form is ______.
    Back
    inactive ; active
  17. Front
    Which two hormones switch fatty acid synthesis OFF (via AMPK phosphorylation of ACC1 )?
    Back
    Glucagon and adrenaline
  18. Front
    Where is the ACC2 isoform primarily found?
    Back
    Heart and skeletal muscle
  19. Front
    What is the function of the malonyl-CoA produced by ACC2 (on the outer mitochondrial membrane )?
    Back
    It inhibits CPT I , blocking fatty acid import into mitochondria for oxidation
  20. Front
    Fatty acid synthase (FAS) is functionally active only in what oligomeric state?
    Back
    As a homodimer
  21. Front
    Which structural domain of FAS carries intermediates between active sites?
    Back
    Acyl carrier protein (ACP)
  22. Front
    What flexible chemical arm of ACP swings intermediates from one active site to the next?
    Back
    The phosphopantetheine arm
  23. Front
    Cloze: The four repeating reactions of each FAS elongation cycle, in order, are condensation → ______ → dehydration → ______.
    Back
    reduction; reduction
  24. Front
    Which cofactor is the electron donor (reducing agent) for the two reduction steps of fatty acid synthesis?
    Back
    NADPH
  25. Front
    How many NADPH are consumed to synthesize one molecule of palmitate ?
    Back
    14 NADPH
  26. Front
    How many NADPH are consumed per two-carbon elongation cycle of FAS ?
    Back
    2 NADPH
  27. Front
    How many rounds of elongation does FAS perform to build palmitate ?
    Back
    7 rounds
  28. Front
    What is the standard end-product of fatty acid synthase , and how many carbons does it have?
    Back
    Palmitate (C16:0)
  29. Front
    Which FAS domain hydrolyzes the finished chain off ACP to release free palmitate ?
    Back
    The thioesterase domain
  30. Front
    Cloze: Palmitate synthesis stoichiometry: 1 acetyl-CoA + ______ malonyl-CoA + 14 NADPH → palmitate + 7 CO2.
    Back
    7
  31. Front
    What is the dominant cytosolic source of NADPH for lipogenesis?
    Back
    The pentose phosphate pathway (hexose monophosphate shunt)
  32. Front
    Which citrate-shuttle enzyme generates NADPH by oxidatively decarboxylating malate to pyruvate ?
    Back
    Malic enzyme
  33. Front
    Why does G6PD deficiency impair lipogenesis?
    Back
    Reduced pentose phosphate pathway activity lowers available NADPH for fatty acid synthesis
  34. Front
    Discrimination — carrier protein: fatty acid SYNTHESIS uses which acyl carrier?
    Back
    ACP (phosphopantetheine)
  35. Front
    Discrimination — carrier protein: beta- OXIDATION uses which acyl carrier?
    Back
    CoA
  36. Front
    Discrimination — electron currency: beta-oxidation PRODUCES which two electron carriers?
    Back
    NADH and FADH2
  37. Front
    Which molecule is the molecular switch linking fatty acid synthesis to inhibition of beta-oxidation ?
    Back
    Malonyl-CoA
  38. Front
    Malonyl-CoA inhibits which enzyme to shut off beta-oxidation?
    Back
    CPT I (carnitine palmitoyltransferase I)
  39. Front
    What is the rate-limiting / committed step controlling fatty acyl import for beta-oxidation?
    Back
    CPT I (carnitine palmitoyltransferase I)
  40. Front
    Discrimination — stereochemistry: the 3-hydroxyacyl intermediate of fatty acid SYNTHESIS is which stereoisomer?
    Back
    D-3-hydroxyacyl-ACP
  41. Front
    Discrimination — stereochemistry: the 3-hydroxyacyl intermediate of beta- OXIDATION is which stereoisomer?
    Back
    L-3-hydroxyacyl-CoA
  42. Front
    In the citrate shuttle , oxaloacetate is reduced to malate by which enzyme (using NADH)?
    Back
    Malate dehydrogenase
  43. Front
    After malic enzyme converts malate to pyruvate , where does the pyruvate go to complete the shuttle?
    Back
    Back into the mitochondria
  44. Front
    Cloze: Insulin increases transcription of the lipogenic enzymes citrate lyase , malic enzyme , ACC1 , and ______.
    Back
    FAS (fatty acid synthase)
  45. Front
    At the level of enzyme expression, which hormones suppress the lipogenic transcriptional program?
    Back
    Glucagon and adrenaline
  46. Front
    Which two compartmentation 'traffic-control' points govern whether carbon flows toward synthesis or oxidation?
    Back
    The citrate shuttle and CPT I
  47. Front
    In the fed state (high insulin ), is fatty acid synthesis or beta-oxidation favored?
    Back
    Fatty acid synthesis ( oxidation is off )
  48. Front
    In which organ does de novo fatty acid synthesis primarily occur?
    Back
    Liver (also adipose tissue and the lactating mammary gland )
  49. Front
    Besides the liver , name the two other tissues where de novo fatty acid synthesis occurs.
    Back
    Adipose tissue and the lactating mammary gland
  50. Front
    How many NADPH does the oxidative branch of the pentose phosphate pathway yield per glucose-6-phosphate processed?
    Back
    2 NADPH
  51. Front
    Which named FAS domain catalyzes the condensation step of each elongation cycle?
    Back
    Beta-ketoacyl-ACP synthase (the KS / condensing-enzyme domain)
  52. Front
    Onto which residue of the condensing enzyme (KS) is the starter acetyl group loaded before condensation?
    Back
    The cysteine-SH (Cys-SH) of the KS domain
  53. Front
    Why is the homodimeric structure of FAS functionally important — how many fatty acid chains are built at once?
    Back
    Two fatty acid molecules are assembled simultaneously, head-to-tail , on the dimer
  54. Front
    Discrimination — electron coenzymes : beta-oxidation uses which two coenzymes as electron ACCEPTORS ?
    Back
    FAD and NAD+
  55. Front
    Cloze: Synthesis uses ______ as the electron DONOR , whereas beta-oxidation uses FAD and NAD+ as electron ACCEPTORS.
    Back
    NADPH
  56. Front
    By what molecular mechanism does citrate allosterically activate ACC1 ?
    Back
    It polymerizes ACC1 into its active filamentous (filament) form
  57. Front
    The lecture organizes fatty acid synthesis regulation into four named levels — what are they?
    Back
    Compartmentation, allosteric effectors, covalent modification, and enzyme expression
  58. Front
    Why is making malonyl-CoA (carboxylate, then later decarboxylate) thermodynamically analogous to a step in gluconeogenesis?
    Back
    Same trick: a carboxylation is added then released as CO2 to drive an otherwise unfavorable reaction forward (as pyruvate carboxylase does in gluconeogenesis)
  59. Front
    Write the balanced committed-step reaction catalyzed by ACC1 .
    Back
    Acetyl-CoA + CO2 + ATP → malonyl-CoA + ADP + Pi
  60. Front
    Discrimination — what ACTIVATES beta-oxidation (the fasted-state signals)?
    Back
    Glucagon, adrenaline, and low energy
  61. Front
    In the fasted state ( glucagon/adrenaline dominate), what happens to fatty acids entering the mitochondria ?
    Back
    They flood in for beta-oxidation or ketogenesis ( ACC1 is phosphorylated/inactive , malonyl-CoA falls, CPT I is free)
  62. Front
    What is AMPK 's role as a cellular sensor, and what activates it?
    Back
    It is the cell's energy sensor — it is activated when AMP rises (low energy) , turning off anabolic processes like fatty acid synthesis
  63. Front
    In each FAS elongation cycle, the dehydration step removes water to create what kind of bond?
    Back
    A trans double bond
  64. Front
    Exam trap — even though malonyl-CoA is the elongating unit, where do ALL the carbons of the final fatty acid come from?
    Back
    Acetyl-CoA (the extra CO2 added to make malonyl-CoA is lost in every cycle )

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