Lipid Metabolism Flashcards Preview

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Flashcards in Lipid Metabolism Deck (35):
1

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

2-carbon units

2

Main substrate for fatty acid biosynthesis

Malonyl-ACP (ACP=acyl carrier protein)
Carboxylated analog of acetyl CoA bound to ACP

3

Synthesis of malonyl-ACP

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

4

Initiation of fatty acid synthesis

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

5

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

ACP

6

Reaction #1 of fatty acid elongation

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

7

Reaction #2 of fatty acid elongation

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

8

Reaction #3 of fatty acid elongation

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

9

End product of fatty acid synthesis

16- and 18-carbon saturated fatty acids
Active site cannot tolerate longer chains

10

Termination of fatty acid synthesis

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

11

Net reaction for synthesis of palmitate (C 16)

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

12

Elongases

Enzymes that use malonyl CoA to extend fatty acid chains

13

Desaturases

Enzymes that introduce unsaturations into fatty acid chains

14

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

Every 3 carbons

15

Desaturase mechanism

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)

16

Elongase mechanism

Malonyl CoA is added onto beginning of fatty acid chain

17

How fatty acids are typically stored

Triacylglycerols

18

Step 1 of triacylglycerol synthesis

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

19

Step 2 of triacylglycerol synthesis

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

20

Step 3 of triacylglycerol synthesis

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

21

Step 4 of triacylglycerol synthesis

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

22

Eicosanoids are derived from what?

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

23

3 stages of biosynthesis of cholesterol

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

24

Key regulatory step in synthesis of isopentenyl diphosphate from acetyl CoA

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

25

How isopentenyl diphosphate is made into squalene

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

26

How squalene is made into cholesterol

Squalene -> lanosterol -> cholesterol

27

Step 1 of fatty acid catabolism

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

28

Step 2 of fatty acid catabolism

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

29

Step 3 of fatty acid catabolism

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

30

Step 4 of fatty acid catabolism

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

31

Insulin

Hormone that increases lipid biosynthesis and storage

32

Glucagon

Hormone that increases lipid catabolism

33

Epinephrine

Hormone that increases lipid catabolism

34

Key regulatory enzyme for lipid metabolism

Acetyl-CoA carboxylase

35

Lipoproteins and serum albumin

Transport fatty acids