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Biochemistry II > Chapter 21 > Flashcards

Chapter 21 Flashcards

1
Q

What are lipids?

A
  • major form of stored energy

- major parts of cell walls

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2
Q

What can lipids become?

A
  • pigments
  • cofactors
  • detergents
  • transporters
  • hormones
  • messengers
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3
Q

Requirements for lipid biosynthesis

A
  • usually ATP

- NADPH as a reduced electron carrier

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4
Q

Anabolic lipid pathways

A

reductive

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5
Q

Catabolic lipid pathways

A

oxidative

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6
Q

What are the two molecules necessary for lipid formation?

A
  • malonyl-CoA

- acetyl-CoA

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7
Q

Draw the structure of malonyl CoA

A

.

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8
Q

Fatty acid biosynthesis and breakdown pathways

A

two different pathways

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9
Q

Fatty acid biosynthesis and breakdown enzymes

A

different enzymes

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10
Q

Fatty acid biosynthesis and breakdown location

A

different parts of the cell

  • catabolism=mito matrix
  • anabolism=cytoplasm
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11
Q

Acetyl-CoA carboxylase action

A
  • catalyzes the one carbon transfer of a carboxyl group from bicarbonate via biotin to acetyl-CoA
  • uses ATP
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12
Q

Biotin and Acetyl-CoA carboxylase

A

biotin forms an amide linkage with the enzyme

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13
Q

Acetyl-CoA carboxylase structure

A

3 multifunctional domains

  • biotin carrier
  • biotin carboxylase
  • transcarboxylase
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14
Q

Fatty acid synthase

A

catalyzes the stepwise addition of acetyl groups by an activated malonyl group forming a fatty acid chain

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15
Q

Final product of fatty acid synthase

A

saturated 16 carbon fatty acid called palmitate

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16
Q

Fatty acid synthase groups

A
  • NADPH serves as a reducing agent

- 2 enzyme thiols serve as activating groups

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17
Q

4 steps in fatty acid synthase

A
  1. condensation
  2. reduction
  3. dehydration
  4. reduction
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18
Q

E. coli fatty acid synthase

A
  • 7 different active sites
  • 7 associated proteins
  • thiols on ACP and KS covalently attach and anchor the reaction intermediates
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19
Q

Acyl carrier protein

A
  • contains 4’-phosphopanthetheine

- 2 other groups identical to coenzyme A

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20
Q

4’-phosphopantetheine

A

serves as a flexible arm moving the reaction intermediates from one active site to the next

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21
Q

Acetyl-CoA -ACP trancacetylase (AT)

A

catalyzes the transfer of an acetyl group from acetyl-CoA to the Cys -SH group of beta-leto acyl-ACP synthase (KS)
-uses the only acetyl-CoA required in fatty acid biosynthesis

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22
Q

Malonyl-CoA -ACP transferase (MT)

A

catalyzes the transfer of a malonyl group from malonyl-CoA to the Cys -SH group of the acyl carrier protein (ACP)

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23
Q

Fatty acid synthesis step 1

A
  • condensation
  • beta-ketoacyl -ACP synthase (KS) catalyzes the condensation of the activated acetyl and malonyl groups to form acetoacetyl-ACP and releasing CO2
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24
Q

CO2 released in step 1

A
  • same carbon from bicarbonate
  • added to acetyl-CoA to activate it
  • coupling the decarboxylation and condensation makes step 1 thermodynamically favorable
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25
Q

Fatty acid synthesis step 2

A

beta-ketoacyl -ACP reductase (KR) catalyzes the reduction of the carbonyl group at C-3 to form beta-hydroxybutyryl -ACP
-uses NADPH

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26
Q

Fatty acid synthesis step 3

A

beta-ketoacyl -ACP dehydrogenase (HD) catalyzes the dehydration to form trans-delta2-butenoyl -ACP

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27
Q

Fatty acid synthesis step 4

A

enoyl -ACP reductase (ER) catalyzes the reduction of the carbon-carbon double bond to form butyryl -ACP
-uses NADPH

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28
Q

Repriming fatty acid synthesis

A
  • the butyryl group is transferred from the Cys -SH on the acyl carrier protein (ACP) to the Cys -SH on beta-ketoacyl -ACP synthase (KS)
  • malonyl-Co A -ACP transferase (MT) transfers another malonyl-CoA to ACP to repeat the process
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29
Q

First acyl group in fatty acid synthesis

A

ends up at the omega end of the fatty acid

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30
Q

Fatty acid synthesis reaction

A 
converts;
-8 acetyl-CoA
-7 ATP
-14 NADPH
-14 H+
to;
-palmitate
-8 CoA
-7 ADP
-7 Pi
-14 NADP-
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31
Q

Stearate

A
  • 18 carbon fatty acid

- small amounts produced

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32
Q

Location of fatty acid synthesis

A
  • cytosol
  • NADPH is high for biosynthesis of fatty acids, nucleotides, amino acids and glucose
  • NADH is now for glycolysis
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33
Q

Plant fatty acid synthesis

A

-in the stoma where light reactions make NADPH

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34
Q

Rate limiting step in fatty acid biosynthesis

A

-acetyl-CoA carboxylase reaction

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35
Q

Acetyl-CoA carboxylase regulation

A
  • negatively allosterically regulated by palmitoyl-CoA
  • positively by citrate
  • hormone triggered phosphorylation inactivates the enzyme
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36
Q

Carnitine acyltransferase 1 regulation

A

inhibited by malonyl-CoA

37
Q

Long chain fatty acid synthesis precursor

A

palmitate

38
Q

Long chain fatty acid synthesis systems

A
  • in mitochondria
  • in smooth ER
  • can elongate
  • can desaturate
39
Q

Plant long chain fatty acid synthesis

A
  • can desaturate to polyunsaturated fatty acids.

- double bonds at 9, 12 and 15

40
Q

Desaturation of fatty acids precursors

A
  • palmitate

- stearate

41
Q

Desaturation of fatty acids enzyme

A

Fatty acyl-CoA desaturase

42
Q

Fatty acyl-CoA desaturase

A
  • catalyzes the oxidation of the saturated fatty acid to a monosaturated fatty acid
  • mixed function oxidase
  • NADPH and fatty acids are oxidized and O2 is reduced to H20
43
Q

Eicosanoid synthesis

A

-from arachidonate

44
Q

Cyclooxygenase (COX)

A
  • bifunctional

- formation of prostaglandins from arachidonate

45
Q

COX inhibitors

A

-aspirin and NSAIDs stop the formation of prostaglandins

46
Q

Aspirin

A

acetylates a Ser in the active of COX irreversibly deactivating it

47
Q

NSAIDs

A

probably inhibit by mimicking the structure of the substrate or reaction intermediate
-competitive inhibitors

48
Q

Problems with aspirin

A
  • block thromboxanes -> clotting is reduced

- decreases stomach mucus, causes problems

49
Q

Thromboxanes

A

produced by blood platelets

  • constrict BV
  • facilitate platelet aggregation
50
Q

Uses of aspirin

A

low doses can reduce the probability of heart attacks and stroke

51
Q

Leukotrienes

A
  • signal smooth muscle contraction

- not effected by COX therefore aspirin and NSAIDs are not a problem

52
Q

Fatt acid fates

A
  • triacyglycerols for energy storage

- glycerophospholipids for membranes

53
Q

Triacylglycerol and glycerophospholipid common precursors

A
  • fatty acyl-CoA

- glycerol 3-phosphate

54
Q

Glycerol 3-phosphate

A
  • from dihydroxyacetone phosphate in glycolysis

- by glycerol 3-phosphate dehydrogenase

55
Q

Fatty acyl-CoA

A

-from fatty acids and CoA via acyl-CoA synthetase

56
Q

Acyl transferases

A

catalyze the transfer of the fatty acyl groups from fatty acyl-CoA to the free hydroxyl groups of glycerol 3-phosphate to form phosphatidic acid or diacylglycerol 3-phosphate

57
Q

Phosphatidic acid

A

precursor to triacylglycerols

58
Q

Complex glycerophospholipid synthesis

A

adding a head group to the phosphate of phosphatidic acid

59
Q

Phosphatidic acid phosphatase

A

catalyzes the hydrolysis of the phosphate group to form 1,2-diacylglycerol

60
Q

Formation of triacylglycerol

A

1,2-diacylglycerol gets another fatty acid

61
Q

Regulation of triacylglycerol synthesis

A
  • hormones (insulin)

- very little regulation

62
Q

Insulin

A

promotes the conversion of carbohydrates and amino acids to triacylglycerols via acetyl-CoA production

63
Q

High blood cholesterol

A

strong correlation with incidence of human cardiovascular disease

64
Q

Cholesterol functions

A
  • cell membranes
  • precursor to steroid based hormones
  • precursor to bile salts
65
Q

Cholesterol in the diet

A
  • not required

- synthesized by every cell in the body

66
Q

Carbons if cholesterol

A

all are from acetate molecules

67
Q

Isoprene molecules

A

essential intermediates between acetate and cholesterol

68
Q

Cholesterol synthesis step 1

A

acetly-CoA to mevalonate

  • uses 3 acetyl-CoA’s condensed to form HMG-CoA with thiolase and HMG-CoA synthase
  • HMG-CoA reductase catalyzes the reduction of HMG-CoA to mevalonate
69
Q

Cholesterol synthesis step 2

A

mevalonate to 2 isoprenes

  • 3 phosphates from ATP go to mevalonate to form 3-phospho-5-pyrophosphomevalonate
  • loses the 3-phospho group and a carboxyl to yield delta3-isopentyl pyrophosphate
  • isomerization then makes dimethyallyl pyrophosphate
70
Q

Cholesterol synthesis step 3

A

6 isoprenes to squalene

  • isopentenyl pyrophosphate and dimethylallyl pyrophosphate condense to make geranyl pyrophosphate which condenses with another isopentenyl to make farnesyl pyrophosphate
  • 2 farnesyl pyrophosphates condense to form squalene
71
Q

Cholesterol synthesis step 4

A

squalene to steroid nucleus

  • squalene converted to squalene 2,3-epoxide via squalene monooxygenase
  • convert to lanosterol via cyclase enzyme
  • 20 reactions from lanosterol to cholesterol
72
Q

Where is cholesterol made?

A

synthesized in the liver

73
Q

Fates of cholesterol

A
  • bile acids
  • cholesteryl esters
  • billary cholesterol
74
Q

Bile acids/salts

A
  • hydrophillic

- aid lipid digestion by emulsification

75
Q

Cholesteryl esters

A
  • have fatty acids attached to hydroxyl group
  • very hydrophobic
  • transferred to other tissues by lipoproteins
76
Q

Cholesterol and lipid transport

A
  • lipoproteins carry in blood plasma

- different lipoproteins

77
Q

Lipoprotein types

A
  • chylomicrons
  • VLDL
  • LDL
  • HDL
78
Q

Chylomicrons

A
  • largest

- move triacylglycerols from the intestines to other tissues

79
Q

VLDL

A
  • formed in the liver from excess dietary fat
  • converted to triacylglycerols
  • travel to muscle and adipose
80
Q

LDL

A
  • move cholesterol from liver to extrahepatic tissue for uptake
  • “bad” cholesterol
81
Q

HDL

A
  • made in the liver and small intestine

- moves through blood converting phospholipids and cholesterol to cholesteryl esters for transport back to the liver

82
Q

Saturated fats

A

can be used to make cholesterol

83
Q

Cholesterol synthesis rate limiting step

A

-conversion of HMG-CoA to mevalonate

84
Q

Regulation of cholesterol sythesis

A
  • rate limiting step
  • insulin and glucagon regulate HMG-CoA reductase
  • High cholesterol levels
85
Q

High cholesterol level regulation

A
  • upregulate cholesteryl ester formation

- downregulate transcription of LDL receptor

86
Q

Atherosclerosis

A

excess cholesterol build up in the arteries, creates obstruction

87
Q

Statins

A
  • structural analogs of mevalonate

- inhibit HMG-CoA reductase

88
Q

Alternative fates of activated isoprene

A
  • vitamins
  • hormones
  • quinone based electron carriers

Biochemistry II (8 decks)

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