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Medical Biochemistry > Ch. 16: Lipids I: FAs & Eicosanoids > Flashcards

Ch. 16: Lipids I: FAs & Eicosanoids Flashcards

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USMLE® Step 1 flashcards
1
Q

How do you define lipids based on their solubility?

A

Soluble in non-polar solvents

Not very soluble in water

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2
Q

Which lipids are polar?

A

FAs
Cholesterol
Glycerophosphatides
Glycosphingolipids

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3
Q

Which lipids are non-polar?

A

Triacylglycerols

Cholesterol esters

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4
Q

Important functions of lipids?

A 
Thermal insulation (most impt)
Energy storage as TG
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5
Q

Difference bet saturated & unsaturated fats?

A

Saturated: No C=C

Unsaturated: C=C

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6
Q

Saturated FAs: Lauric acid

Molecular formula?

A

C12 H24 O2

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7
Q

Saturated FAs: Myristic acid

Molecular formula?

A

C14 H28 O2

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8
Q

Saturated FAs: Palmitic acid

Molecular formula?

A

C16 H32 O2

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9
Q

Saturated FAs: Stearic acid

Molecular formula?

A

C18 H36 O2

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10
Q

Saturated FAs: Arachidic acid

Molecular formula?

A

C20 H40 O2

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11
Q

FA Oxidation: how many net ATP made from 16C fat?

A

129 net ATP

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12
Q

Hormones that bind to receptors to metabolize TAG ➡️ DAG + FA?

3 enzymes involved?

A

Epinephrine, glucagon

1) adenylate cyclase
2) protein kinase
3) hormone-sensitive lipase

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13
Q

⬆️ FA oxidation indicative of what?

What is ⬆️ produced in liver? Made from what?

A

Starvation
DM

Ketone bodies
Acetyl CoA

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14
Q

Name 3 acyl-CoA synthases & what FAs they act on.

A

Acetyl-CoA synthase: acetate & low wt carboxylic acids

Medium-chain acyl-CoA synthase: FAs w/4-11 C

Acyl-CoA synthase: FAs w/6-20 C

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15
Q

How many ATP needed to activate FAs?

A

2 ATP used (➡️ 131-2 = 129 net ATP)

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16
Q

Activation step: FA + CoASH ➡️ acyl-CoA (thioester), using 2 ATP

Location? Enzyme involved?

A

On outer mitochondrial membrane

Acyl-CoA synthetase

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17
Q

Carnitine is synthesized from which a.a.?

A

Lys & Met

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18
Q

Transport of acyl-CoA ➡️ mitochondrial matrix:

1) Acyl-CoA + carnitine ➡️ ?
Enzyme?
Location of rxn?

A

Acylcarnitine + CoASH

Carnitine palmitoyl-transferase I (CPT I)
Intermembrane space

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19
Q

Transport of acyl-CoA ➡️ mitochondrial matrix:

2) Acylcarnitine ➡️ moved into mitochondrial matrix
Enzyme?

A

Carnitine-acylcarnitine translocase

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20
Q

Transport of acyl-CoA ➡️ mitochondrial matrix:

3) Acylcarnitine + CoASH ➡️ ?
Enzyme?
Location?

A

Acyl-CoA + carnitine

Carnitine-palmitoyl transferase II (CPT II)
mitochondrial matrix

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21
Q

What is an allosteric ➖ of CPTI in liver?

Fxn?

A

Malonyl CoA (Precursor for FA synthesis)

Prevents simultaneous FA oxidation & sythesis

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22
Q

What generally occurs in beta-oxidation?

1 run through cycle makes how much ATP?

A

Oxidation of acyl-CoA at beta C ➡️ 2 Cs removed as acetyl CoA

17 ATP

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23
Q

Beta oxidation: step 1?

Enzyme?

A

Acyl-CoA ➡️ alpha,beta-unsat. acyl-CoA / delta^2-unsat. acyl-CoA + FADH2

Acyl-CoA dehydrogenase

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24
Q

Beta oxidation: step 2?

Enzyme?

A

Alpha,beta- or delta^2-unsat. acyl-CoA ➡️ L-beta-hydroxyacyl-CoA

Enoyl-CoA hydratase

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25
Q

Beta oxidation: step 3?

Enzyme?

A

L-beta-hydroxyacyl-CoA ➡️ beta-ketoacyl-CoA + NADH

L-beta-hydroxyacyl-CoA dehydrogenase

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26
Q

Beta oxidation: step 4?

Enzyme?

A

Beta-ketoacyl-CoA ➡️ acyl-CoA + acetyl-CoA

3-ketoacyl-CoA thiolase

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27
Q

What can be done with the acetyl CoA produced from beta-oxidation?

A

1) TCA cycle
2) cholesterol synthesis (in cytosol)
3) form ketone bodies (liver)

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28
Q

Beta-oxidation energetics: palmitate

How are 129 ATP obtained? (Breakdown)

A

7 FADH2 x 2 = 14 ATP
7 NADH x 3 = 21 ATP
8 acetyl CoA x 12 = 96 ATP
- 2 ATP (FA activation)

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29
Q

Regulation of FA oxidation:

Lipogenesis: ➕ and ➖ of acetyl-CoA carboxylase? (➖ and ➕ of FA oxidation)

A

➕ (➖ FA oxidation): insulin

➖ (➕ FA oxidation): Acyl-CoA, glucagon

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30
Q

How are VLCFAs (20 C or longer) oxidized?

A

1) initial beta-oxidation in peroxisomes (no ATP yield)

2) shortened FAs (LCFAs) ➡️ mitochondria for further oxidation

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31
Q

What happens to the FADH2 produced in peroxisomal FA oxidation?

A

oxidized by O2 ➡️ H2O2 by catalase

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32
Q

3 disorders in peroxisomal FA oxidation? What occurs?

A 
Zellweger's syndrome (formation of peroxisomes)
Neonatal adrenoleukodystrophy (⬇️ breakdown of VLCFAs)
Childhood adrenoleukodystrophy (same as #2)

Accumulation of VLCFAs in liver & CNS ➡️ severe neuro problems, death

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33
Q

What are sources of propionyl CoA?

A

Odd number FA oxidation

Catabolism of Ile, Val, Met, Thr

Oxidation of side chain of cholesterol

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34
Q

Oxidation of propionyl-CoA ➡️ ? ➡️ ? or ?

Reactions require what vitamins?

A

Succinyl-CoA ➡️ oxidized or converted to glucose

Biotin
Vit B12

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35
Q

What generally occurs in alpha-oxidation of FAs?

A

Oxidation of LCFA ➡️ 2-OH FA ➡️ oxidation to FA w/one less C

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36
Q

Alpha-oxidation disorders: Refsum’s disease?

Resulting conditions?

A

Deficiency of phytanoyl-CoA hydroxylase ➡️ accumulation of phytanic acid

Retinitis pigmentosa, failing night vision, peripheral neuropathy, cerebellar ataxia

37
Q

What generally occurs in omega-oxidation of FAs?

Catalyzed by a monooxygenase that requires ?

A

Oxidation of C atom most remote from carboxyl group in FA

NADPH, O2, P-450

38
Q

What are the products of omega oxidation of FAs?

A

Dicarboxylic acids ➡️ further oxidized from either end

39
Q

How does oxidation of mono- & poly-unsaturated FAs differ?

A

Skips FAD+ step (since double bond already present)

40
Q

General steps of ketone metabolism?

A

2 acetyl CoA ➡️ acetoacetyl CoA (+ acetyl CoA in) ➡️ HMG CoA ➡️ acetoacetate (+ acetyl CoA out) ➡️ acetone or 3-hydroxybutyrate

41
Q

3 ketones generated in the body?

A

Acetoacetate
Acetone
3-hydroxybutyrate

42
Q

Where does ketogenesis take place? Cholesterol synthesis?

A

Ketogenesis: mitochondria

Cholesterol synthesis: cytosol

43
Q

How are ketone bodies generated in liver used by extra hepatic tissues?

A

1) 3-hydroxybutyrate ➡️ acetoacetate
2) Acetoacetate + succinyl CoA (TCA) ➡️ acetoacetyl CoA + succinate (TCA) (via thiophorase)
3) Acetoacetyl CoA ➡️ 2 acetyl CoA ➡️ TCA cycle

44
Q

Regulation of ketogenesis: 1st point?

A

Lipolysis (TAG ➡️ FFA in adipocytes)

➕: glucagon, epi

45
Q

Regulation of ketogenesis: 2nd point?

A

Transport of acyl CoA into MT matrix: Carnitine-palmitoyl transferase I (CPT-I)

➖: ⬆️ malonyl CoA

46
Q

Regulation of ketogenesis: 3rd point?

A

Acetyl CoA ➡️ ketogenesis or TCA?

Starvation: shunts acetyl CoA to ketogenesis (➖ TCA since oxaloacetate ➡️ PEP in gluconeogenesis)

47
Q

What are long chain fatty acids synthesized from?

A

Dietary glucose (via pyruvate)

48
Q

Where are the enzymes for fatty acid synthesis located in cell?

A

Cytosol (different enzymes from FA breakdown)

49
Q

What is required for FA synthesis?

A 
Reduced NADPH (from HMP shunt)
ATP
50
Q

What is initial & control step in FA synthesis?

Enzyme? Requires what co-factor?

A

Acetyl CoA ➡️ Malonyl CoA
(CO2 transfered from HCO3- ➡️ enzyme ➡️ acetyl CoA)

Acetyl CoA carboxylase (requires biotin)

51
Q

What are the 8 proteins (7 enzymes + carrier protein) that make up the FA synthase multi-enzyme complex?

A 
Ketoacyl synthase
Acetyl transacylase
Malonyl transacylase
Hydratase
Enoyl reductase
Ketoacyl reductase
Acyl carrier protein (ACP)
Thioesterase
52
Q

FA synthase multi-enzyme complex: What vitamin does the acyl carrier protein (ACP) need?

What important residue does it contain?

A

Pantothenic acid (4’-P-panthotheine)

Contains SH residue (ketoacyl synthase also contains SH from Cys)

53
Q

Where does the first acetyl group come from (to start FA synthesis)?

What provides subsequent acetyl groups?

A

Acetyl CoA (“seed”)

Malonyl CoA

Ex: C15 & C16 of palmitate is from acetyl CoA ➡️ C1-C14 from Malonyl CoA

54
Q

What are the first 5 reactions (in order) of FA synthesis? Enzymes for each step?

A

1) priming reaction (acetyl transacylase / malonyl transacylase)
2) condensation (beta-ketoacyl synthase)
3) 1st reduction w/NADPH (beta-ketoacyl reductase)
4) dehydration (beta-hydroxyacyl dehydratase)
5) 2nd reduction w/NADPH (enoyl reductase)

55
Q

After first 5 reactions of FA synthesis, what are the 2 possible following steps?

A

If acyl group is 16 C: enzyme loses affinity, releases palmitate (via thioester hydrolase)

If acyl group is not yet 16 C: acyl group transferred to beta-ketoacyl synthase, return to reaction 1

56
Q

What are the 3 generators of NADPH in the cytosol? (➡️ used in lipogenesis)

A

1) pentose P pathway
2) isocitrate dehydrogenase
3) malic enzyme

57
Q

How is acetyl CoA used in lipogenesis obtained?

A

MT: Acetyl CoA + oxaloacetate ➡️ Citrate, moved out of MT ➡️ cytosol (via anti-port w/malate) ➡️ oxaloacetate + acetyl CoA (via ATP citrate lyase)

58
Q

How are FAs with > 16 C (18-24 Cs) made?

A

Elongation of palmitate in ER or MT (liver)

59
Q

What are the two essentials FAs? (Common name, omega series, systematic name, formula)

A

Linoleic acid (omega 6; 9,12-octadecadienoic; C18 H32 O2)

Alpha-linolenic acid (omega 3; 9,12,15-octadecatrienoic; C18 H30 O2)

60
Q

What important compounds are derived from the 2 essential FAs?

A

Linoleic acid ➡️ arachidonic acid

Alpha-linolenic acid ➡️ docosahexaenoic acid (DHA)

61
Q

Almost all naturally occurring, unsaturated LCFAs exist as which isomer?

A

Cis isomer

62
Q

Unsaturated FAs: Palmitoleic acid

Systematic name? Molecular formula? Omega series?

A

9-hexadecenoic

C16 H30 O2

Omega 7

63
Q

Unsaturated FAs: Oleic acid

Systematic name? Molecular formula? Omega series?

A

9-octadecenoic

C18 H34 O2

Omega 9

64
Q

Unsaturated FAs: Arachidonic acid

Systematic name? Molecular formula? Omega series?

A

5,8,11,14-eicosatetraenoic

C20 H32 O2

Omega 6

65
Q

Main 2 functions of unsaturated FAs?

A

1) fluidity of TG reserves, phospholipid membranes

2) precursors of eicosanoids

66
Q

What are the 2 most common monounsaturated FAs in mammals?

How are their double bonds introduced?

A

Palmitoleic acid
Oleic acid

ER: double bond (bet C9-C10) via FA oxygenase (requires O2 & NADPH)

67
Q

Arachidonic acid is precursor for what 4 compounds?

A

Prostaglandins (via cyclooxygenase)
Thromboxanes
Prostacyclins

Leukotrienes (via 5-lipoxygenase)

68
Q

How are EFAs (precursor FAs) stored?

How are they released?

A

As esters of 2-position of glycerol backbone of cell membrane phospholipids

Activation of appropriate phospholipase

69
Q

What activates phospholipase A2 ➡️ release arachidonic acid?

A

Stimuli ➡️ Intracellular Ca2+ w/calmodulin ➡️ activates phospholipase A2 (and C)

70
Q

What inhibits phospholipase A2 activity?

A

Glucocorticoids (cortisol)

71
Q

Inhibitors of cyclooxygenase?

A

Aspirin
Indomethacin

Selective for COX2: Celecoxib, Rofecoxib

72
Q

Synthesis of prostanoids: first 3 substrates?

A

Arachidonic acid ➡️ PGG2 ➡️ PGH2

73
Q

Synthesis of prostanoids: 5 pathways from PGH2

PGH2 ➡️ PGI2 (➡️ 6-keto-PGF-1alpha)

Enzyme?

A

prostacyclin synthase

74
Q

Synthesis of prostanoids: 5 pathways from PGH2

PGH2 ➡️ PGE2

Enzyme?

A

PGE2 endoperoxide isomerase

75
Q

Synthesis of prostanoids: 5 pathways from PGH2

PGH2 ➡️ PGD2

Enzyme?

A

PGD2 endoperoxide isomerase

76
Q

Synthesis of prostanoids: 5 pathways from PGH2

PGH2 ➡️ PGF-2alpha

Enzyme?

A

PGF-2alpha endoperoxide isomerase

77
Q

Synthesis of prostanoids: 5 pathways from PGH2

PGH2 ➡️ TXA2 (➡️TXB2)

Enzyme?

A

Thromboxane synthase

78
Q

Eicosanoids: PGD2

Major site of synthesis? Major biological activities?

A

Mast cells

➖ platelet & leukocyte aggregation
➕ vasodilation, cAMP levels
⬇️ T cell proliferation, lymphocyte migration, IL-1a, IL-2

79
Q

Eicosanoids: PGE2

Major site of synthesis? Major biological activities?

A

Kidney, spleen, heart

➕vasodilation, cAMP levels
➕ uterine contractions
➕ platelet aggregation
Keeps fetal ductus arteriosus open
⬇️ T cell proliferation, lymphocyte migration, IL-1a, IL-2
80
Q

Eicosanoids: PGF-2 alpha

Major site of synthesis? Major biological activities?

A

Kidney, spleen, heart

➕ vasoconstriction
➕ bronchoconstriction
➕ smooth muscle contraction

81
Q

Eicosanoids: PGH2

Major biological activities?

A

➕ platelet & leukocyte aggregation

➕ vasoconstriction

82
Q

Eicosanoids: PGI2

Major site of synthesis? Major biological activities?

A

Heart, vascular, endothelial cells

➖ platelet aggregation & leukocyte aggregation
➕ vasodilation, cAMP levels
⬇️ T cell proliferation, lymphocyte migration, IL-1a, IL-2

83
Q

Eicosanoids: TXA2

Major site of synthesis? Major biological activities?

A

Platelets

➕ platelet aggregation
➕ vasoconstriction
➕ lymphocyte proliferation
➕ bronchoconstriction

84
Q

Eicosanoids: TXB2

Major site of synthesis? Major biological activities?

A

Platelets

➕ vasoconstriction

85
Q

Eicosanoids: LTB4

Major site of synthesis? Major biological activities?

A

Neutrophils, monocytes, eosinophils, basophils, mast cells, epithelial cells

vascular permeability
➕ leukocyte chemotaxis & aggregation
T cell proliferation, INF-gamma, IL-1, IL-2

86
Q

Eicosanoids: LTC4

Major site of synthesis? Major biological activities?

A

Monocytes & alveolar macs, Eosinophils, Basophils, Mast cells, Epithelial cells

➕ Microvascular vasoconstrictor
Vascular permeability
➕ Bronchoconstriction
➕ INF-gamma 
Part of SRS-A
87
Q

Eicosanoids: LTD4

Major site of synthesis? Major biological activities?

A

Monocytes & alveolar macs, eosinophils, mast cells, epithelial cells

➕ Microvascular vasoconstrictor
Vascular permeability
➕ Bronchoconstriction
MAIN part of SRS-A
➕ INF-gamma
88
Q

Eicosanoids: LTE4

Major site of synthesis? Major biological activities?

A

Basophils, mast cells

Microvascular vasoconstrictor
Bronchoconstriction
Part of SRS-A

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