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Med Chem > Lipid Metabolism > Flashcards

Lipid Metabolism Flashcards

1
Q

Units of what carbon length are added to a growing hydrocarbon chain?

A

2-carbon units

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2
Q

Main substrate for fatty acid biosynthesis

A

Malonyl-ACP (ACP=acyl carrier protein)

Carboxylated analog of acetyl CoA bound to ACP

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3
Q

Synthesis of malonyl-ACP

A
  1. Carboxylation of acetyl CoA (catalyzed by acetyl-CoA carboxylase bound to biotin)
  2. Transacylation from CoA to ACP
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4
Q

Initiation of fatty acid synthesis

A

Acetoacetyl-ACP (also referred to as 3-ketoacyl ACP) is synthesized from acetyl CoA and malonyl ACP (catalyzed by 3-ketoacyl ACP synthase)

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5
Q

“Newest” 2-carbon unit is closest to what in the growing chain?

A

ACP

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6
Q

Reaction #1 of fatty acid elongation

A

Reduction of a ketone to a secondary alcohol
3-ketoacyl ACP -> D-3-hydroxyacyl ACP
Enzyme: 3-ketoacyl-ACP reductase

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7
Q

Reaction #2 of fatty acid elongation

A

Dehydration of a secondary alcohol to a trans-alkene
D-3-hydroxyacyl ACP -> trans-delta2-enoyl ACP
Enzyme: 3-hydroxyacyl-ACP dehydratase

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8
Q

Reaction #3 of fatty acid elongation

A

Reduction of a trans-alkene to an alkane
Trans-delta2-enoyl ACP -> acyl ACP
Enzyme: enoyl-ACP reductase

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9
Q

End product of fatty acid synthesis

A

16- and 18-carbon saturated fatty acids

Active site cannot tolerate longer chains

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10
Q

Termination of fatty acid synthesis

A

Palmitoyl ACP is hydrolyzed by thioesterase to form palmitate (C 16) + HS-ACP

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11
Q

Net reaction for synthesis of palmitate (C 16)

A

Acetyl CoA + 7 malonyl CoA + 14 NADPH + 14 H+ -> palmitate + 7 CO2 + 14 NADP+ + 8 HS-CoA + 6 H2O

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12
Q

Elongases

A

Enzymes that use malonyl CoA to extend fatty acid chains

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13
Q

Desaturases

A

Enzymes that introduce unsaturations into fatty acid chains

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14
Q

Polyunsaturated fatty acids usually have their unsaturations introduced every how many carbons?

A

Every 3 carbons

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15
Q

Desaturase mechanism

A

Molecular O2 is used as oxidant to oxidize single bond to double bond
NADH is oxidized to NAD+ (2 electrons) and O2 is reduced to 2 H2O (4 electrons)

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16
Q

Elongase mechanism

A

Malonyl CoA is added onto beginning of fatty acid chain

17
Q

How fatty acids are typically stored

A

Triacylglycerols

18
Q

Step 1 of triacylglycerol synthesis

A

Glycerol 3-phosphate + acyl CoA -> 1-acylglycerol-3-phosphate (carbonyl carbon attached to -OH of C1)
Enzyme: glycerol 3-phosphate acyltransferase

19
Q

Step 2 of triacylglycerol synthesis

A

1-acylglycerol-3-phosphate + acyl CoA -> phosphatidate (carbonyl carbon attached to -OH of C2)
Enzyme: 1-acylglycerol-3-phosphate acyltransferase

20
Q

Step 3 of triacylglycerol synthesis

A

Phosphatidate -> 1,2-diacylglycerol (-PO3 of C3 is replaced with -OH)
Enzyme: Phosphatidate phosphatase

21
Q

Step 4 of triacylglycerol synthesis

A

1,2-diacylglycerol + acyl CoA -> triacylglycerol (carbonyl carbon attached to -OH of C3)
Enzyme: diacylglycerol acyltransferase

22
Q

Eicosanoids are derived from what?

A

Arachidonic acid (20:4 delta 5,8,11,14)

23
Q

3 stages of biosynthesis of cholesterol

A
  1. Acetyl CoA (2C) to isopentenyl diphosphate (5C)
  2. Isopentenyl diphosphate (5C) to squalene (30C)
  3. Squalene (30C) to cholesterol (27C)
24
Q

Key regulatory step in synthesis of isopentenyl diphosphate from acetyl CoA

A

3-hydroxy-3-methylglutaryl CoA (HMG CoA) -> mevalonate
Reduction of thioester to primary alcohol
Enzyme: HMG-CoA reductase

25
Q

How isopentenyl diphosphate is made into squalene

A

2 prenyl transfer reactions (5C + 5C and then 10C + 5C) yield farnesyl diphosphate (15C)
2 farnesyl diphosphates are combined to form squalene (30C)

26
Q

How squalene is made into cholesterol

A

Squalene -> lanosterol -> cholesterol

27
Q

Step 1 of fatty acid catabolism

A

Fatty acyl CoA -> trans-delta2-enoyl CoA
Oxidation of an alkane to an alkene
Enzyme: acyl-CoA dehydrogenase

28
Q

Step 2 of fatty acid catabolism

A

Trans-delta2-enoyl CoA -> L-3-hydroxyacyl CoA
Hydration of an alkene to a secondary alcohol
Enzyme: 2-enoyl-CoA hydratase

29
Q

Step 3 of fatty acid catabolism

A

L-3-hydroxyacyl CoA -> 3-ketoacyl CoA
Oxidation of a secondary alcohol to a ketone
Enzyme: L-3-hydroxyacyl-CoA dehydrogenase

30
Q

Step 4 of fatty acid catabolism

A

3-ketoacyl CoA -> fatty acyl CoA (shortened by 2 carbon atoms) + acetyl CoA
Thiolysis
Enzyme: 3-ketoacyl-CoA thiolase

31
Q

Insulin

A

Hormone that increases lipid biosynthesis and storage

32
Q

Glucagon

A

Hormone that increases lipid catabolism

33
Q

Epinephrine

A

Hormone that increases lipid catabolism

34
Q

Key regulatory enzyme for lipid metabolism

A

Acetyl-CoA carboxylase

35
Q

Lipoproteins and serum albumin

A

Transport fatty acids

Med Chem (37 decks)

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