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MCB 3010 > FINAL EXAM: Hormone, lipid > Flashcards

FINAL EXAM: Hormone, lipid Flashcards

1
Q

catabolism of fatty acids

A

produces acetyl-CoA
produces reducing power (NADH, FADH2)
takes place in mitochondria

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2
Q

Anabolism of fatty acids

A

requires acetyl-CoA and malonyl-CoA (chief substrate)
requires reducing power from NADPH
cytosol in animals; chloroplast in plants (where NADPH is present)

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3
Q

fatty acids are built in several passes

A

processing one acetate unit (2 carbons) at a time

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4
Q

where does the acetate come from in fatty acid synthesis?

A

activated malonate in the form of malonyl-CoA (Acetyl-CoA with another carboxyl)

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5
Q

malonyl-CoA synthesis

A

first committed step of synthesis of fatty acids

rate limiting step

energy from ATP used to add carboxyl group to acetyl-CoA

loss of carboxyl group will provide energy for condensation of acetyl group onto growing FA chain

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6
Q

what provides energy for condensation of acetyl group onto growing FA chain?

A

loss of carboxyl group

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7
Q

malonyl-CoA is formed from

A

acetyl-CoA and bicarbonate

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8
Q

malonyl-CoA formation from acetyl-CoA and bicarbonate

A

reaction carboxylates acetyl CoA

bicarbonate is the source of CO2

catalyzed by: acetyl-CoA carboxylase

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9
Q

acetyl-CoA carboxylase

A

catalyzes malonyl-CoA formation in 3 reactions

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10
Q

3 reactions of acetyl-CoA carboxylase

A

CO2 is activated by phosphorylation by ATP

biotin (cofactor) receives CO2

CO2 transferred to acetyl-CoA

**animals: all on one polypeptide chain in one enzyme)

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11
Q

Fatty acid synthase (FAS)

A

catalyzes synthesis of fatty acids

repeating 4 step sequence that elongates the fatty acyl chain by 2 carbons at each step

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12
Q

FAS mechanism

A

uses NADPH as electron donor (2 redox in reverse; reduce FA, oxidize NADPH)

uses 2 -SH groups on FAS as activating group

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13
Q

FAS in vertebrates and fungi

A

FAS I

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14
Q

FAS in plants and bacteria

A

FAS II

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15
Q

FAS 1

A

focus

single pp chain in verts

leads to single product: palmitate (16:0)

C15 and C16 are from the acetyl-CoA used to prime the reaction

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16
Q

FAS 2

A

made of separate, diffusible enzymes

makes many products (saturated, unsaturated, branched, many lengths)

plants and bacteria

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17
Q

goal of fatty acid synthesis

A

attach 2C acetate unit from malonyl-CoA to a growing chain then reduce it

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18
Q

Fatty acid synthesis reaction 4 enzyme catalyzed steps

A

condensation

reduction

dehydration

reduction

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19
Q

condensation in fatty acid synthesis

A

condensation of growing chain with activated acetate

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20
Q

reduction of fatty acid synthesis

A

reduction of carbonyl to hydroxyl

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21
Q

dehydration of fatty acid synthesis

A

alcohol to trans-alkene

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22
Q

reduction 2 of fatty acid synthesis

A

reduction of alkene to alkane

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23
Q

fatty acid synthesis : chain stuff

A

growing chain is initially attached to a cys on FA synthase via a thioester linkage

during condensation: growing chain is transferred to acyl carrier protein

after each 4 steps, elongated chain is transferred back to the cys of fatty acid synthase

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24
Q

Acyl carrier protein (ACP)

A

shuttle in fatty acid synthesis

covalently attached prosthetic group 4’-phosphopantetheine

delivers acetaldehyde (first step) or malonate (next steps) to FAS

shuttles growing chain from one active site to another during the four step reaction

part of FAS1

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25
Q

4’-phosphopantetheine

A

prosthetic group on ACP

flexible arm to tether acyl chain while carrying intermediates from one enzyme subunit to the next

sulfhydryl group binds to form thioester

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26
Q

general 4 step FAS1 reaction in mammals: PREP

A

ACP binds acetyl group from acetyl CoA (CoA released)

ACP transfers acetyl group to cys on FAS1 (or fatty acyl chain later rounds)

ACP binds malonyl CoA and CoA leaves

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27
Q

general 4 step FAS1 reaction in mammals: Step 1

A

condensation reaction attaches the attached acetyl group (or longer fatty acyl chain) to 2C from malonyl group

  • released CO2 from malonyl group
  • released acetyl group from cys

**decarboxylation (loss of CO2 facilitates the reaction)

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28
Q

general 4 step FAS1 reaction in mammals: Step 2

A

1st reduction

NADPH reduces the beta-keto intermediate to an alcohol

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29
Q

general 4 step FAS1 reaction in mammals: step 3

A

dehydration

OH group from beta carbon and H from alpha carbon are eliminated, creating trans-alkene double bond (and releases water)

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30
Q

general 4 step FAS1 reaction in mammals: step 4

A

2nd reduction

NADPH reduces double bond to yield saturated alkane

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31
Q

end product of FAS1 reaction

A

saturated acyl group lengthened by 2 carbons

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32
Q

product of first round of FAS1

A

butyryl-ACP (bound to sulfur of ACP)

butyryl group transferred to cys of FAS1

new malonyl group from malonyl-CoA binds to ACP

after new round of 4 steps: 6C product is made and bound to ACP

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33
Q

stoichiometry of synthesis of palmitate (16:0)

A

7 AcCoA + 7 CO2 + 7 ATP

**7 acetyl-CoAs are carboxylated to make 7 malonyl-CoA using ATP

7 Malonyl-CoA + 7ADP + 7Pi

** 7 cycles of condensation, reduction, dehydration, reduction using NADPH to reduce the beta-keto group and trans-double bond

Palmitate + 7 CO2 (off Malonyl) + 8 CoA + 14 NADP+ + 6 H2O

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34
Q

why are only 6 H2O made in palmitate synthesis not 7?

A

1 H2O lost to hydrolyzing palmitate off the enzyme

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35
Q

in nonphotosynthetic eukaryotes:

A

acetyl-CoA made in mitochondria but
fatty acids made in cytosol

acetyl-CoA is transported indirectly into cytosol with cost of 2 ATP per Acetyl-CoA

** cost of FA synthesis is 3 ATPs per 2C unit
(1 for malonyl CoA, 2 for transport)

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36
Q

how is Acetyl-CoA which is generated in the mitochondria shuttled to the cytosol?

A

Acetyl-CoA is converted to citrate

Acetyl-CoA + oxaloacetate = citrate

catalyzed by citrate synthase

passes through citrate transporter in inner membrane

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37
Q

what happens to the citrate now in cytosol?

A

cleaved by citrate lyase

regenerates Acetyl-CoA and oxaloacetate

requires ATP

Acetyl-CoA can now be used for lipid synthesis

38
Q

what happens to the oxaloacetate now in the cytosol after citrate is cleaved?

A

malate dehydrogenase reduces oxaloacetate to malate

39
Q

2 fates for malate in cytosol

A

1 - converted in cytosol to pyruvate via malic enzyme (produces NADPH)

NADPH used for lipid synthesis
Pyruvate sent back to mitochondria via pyruvate transporter
converted back to oxaloacetate by pyruvate carboxylase, requires ATP

2 - transported back into mitochondria via malate/alpha-ketoglutarate transporter where it is oxidized to oxaloacetate

40
Q

acetyl-CoA carboxylase regulation of fatty acid synthesis

A

Acetyl-CoA carboxylase: catalyzes the rate-limiting step (acetyl-CoA to malonyl-CoA)

inhibited by: palmitoyl-CoA
activated by: citrate

41
Q

what does citrate signal?

A

excess energy to be converted to fat

in CAC: citrate is made from acetyl-CoA
When [acetyl-CoA] increases in mitochondria, citrate is synthesized and exported to cytosol when ATP is high

42
Q

regulation of FA synthesis in plants and bacteria

A

regulation in plants and bacteria does not rely on citrate

plant acetyl-CoA carboxylase is activated by changes during light reaction of photosynthesis

bacteria use lipids for membranes, not for energy storage
- have complex regulation with guanine nucleotides — coordinates with cell growth/ division

43
Q

transport or attachment of FA requires conversion to

A

Fatty acyl-CoA

44
Q

palmitate can be lengthened to longer chain FA

A

elongation systems in the endoplasmic reticulum and mitochondria create longer FA

each step adds 2C

Stearate (18:0) is the most common product
- one more 2C unit

45
Q

palmitate and stearate can be desaturated

A

Palmitate (16:0) —> palmitoleate (16:1 d9)

stearate (18:0) —> oleate (18:1 d9)

46
Q

what catalyzes the desaturation of palmitate and stearate

A

fatty acyl-CoA desaturase

47
Q

fatty acyl-CoA desaturase

A

O2 reduced to make 2H2O and FA oxidized to produce cis double bond — needs 4 electrons

2 e- and 2H+ come from saturated FA for O2 reduction

2 e- come from oxidation of 2 cytochrome b5

cyt b5 re-reduced by cyt b5 reductase using FADH2

FAD re-reduced by NADPH - NADP+ is formed

  • *oxygen is reduced to water and FA and NADPH are oxidized
    • Bond between C9 and C10 is oxidized
48
Q

plants can desaturate at positions beyond C9

A

humans have: d4, d5, d6, d9 desaturases but not beyond d9

plants:
linoleate 18:2 d9,12
alpha-linoleate 18:3 d9,12,15

these are essential to humans to help control membrane fluidity (polyunsaturated FA = more fluid)

49
Q

precursor for backbone of fat and phospholipids

A

glycerol 3-P

50
Q

most glycerol -3P comes from

A

reducing dihydroxyacetone phosphate from glycolysis via glycerol 3P dehydrogenase

some DHAP made through start of gluconeogenesis

some G3P made from glycerol via glycerol kinase with ATP (liver, kidney)

51
Q

phosphatidic acid

A

glycerol 3P bound by 2 FA on C1 and C2

precursor to triacylglycerols and phospholipids

FA are attached to glycerol-3P by acyl transferases

releases CoA

52
Q

acyl transferases

A

attaches FA to glycerol-3P and releases CoA

53
Q

advantages of making phosphatidic acid

A

can be made into triacylglycerol or glycerophospholipid

triacyl: remove Pi, add FA
glycero: add head group on Pi

54
Q

phosphatidic acid phosphatase

A

MAKES TRIACYLGLYCEROL

removes phosphate from phosphatidic acid

yields 1,2-diacylglycerol

hydroxyl on 3C is acylated with 3rd FA by acyl transferase

yields triacylglycerol

55
Q

peptide hormones

A

insulin and glucagon

bind to receptors that span the membrane and induce conformational change that produces a second messenger

results in signal amplification and changes at many targets

56
Q

insulin signaling pathway

A

RTK, phosphorylation

inc. cell proliferation/growth

lipid synthesis
glucagon synthesis
protein synthesis
glucose uptake

57
Q

glucagon signaling pathway

A

GPCR activates

58
Q

insulin

A

synthesized by beta cells of pancreas as preproinsulin

processed in 2 steps into active form (irreversible covalent regulation)

secreted in response to high glucose after a meal; gets glucose out of blood

59
Q

glucagon

A

synthesized by alpha cells of pancreas as proglucagon

cleaved into active form

synthesized when insulin levels drop in response to lower glucose; increases blood glucose

60
Q

peptide hormone insulin

A

insulin is produced to lower blood sugar

take up glucose into cells from blood
utilize glucose-glycolysis, glycogen synthesis, fatty acid synthesis
prevent intracellular production of glucose
prevent utilization of other molecules for energy

61
Q

affects of insulin

A

binds to receptors in muscle, brain, liver, adipose

muscle and liver: promotes glucose uptake, glycogen synthesis

adipocytes: promotes triacylglycerol synthesis and inhibits breakdown of ^

62
Q

effects of insulin on blood glucose:

inc glucose uptake (muscle, adipose)

A

target enzyme:

inc. glucose transporter GLUT4

63
Q

effects of insulin on blood glucose:

inc glucose uptake (liver)

A

target enzyme:

inc. glucokinase expression

64
Q

effects of insulin on blood glucose:

inc glycogen synthesis (liver, muscle)

A

inc. glycogen synthase

65
Q

effects of insulin on blood glucose:

dec. glycogen breakdown (liver, muscle)

A

dec glycogen phosphorylase

66
Q

effects of insulin on blood glucose:

inc. glycolysis, acetyl-CoA production (liver, muscle)

A

inc PFK-1 by PFK2 (allosteric)

inc pyruvate dehydrogenase complex

67
Q

effects of insulin on blood glucose:

inc. fatty acid synthesis (liver)

A

inc. acetyl-CoA carboxylase

68
Q

effects of insulin on blood glucose:

inc triacylglycerol synthesis (adipose)

A

inc lipoprotein lipase

69
Q

carb metabolism in liver

A

hepatocytes:

  • GLUT2 transporter for diffusion of glucose in/out
  • glucokinase (hexokinase IV)
70
Q

glucokinase

A

in hepatocytes

produces glucose-6P from glucose transported into hepatocyte by GLUT2

higher Km than other hexokinases (10mM vs 4) — glucose-6P isn’t made when glucose is low

NOT INHIBITED BY GLUCOSE-6P so glucose-6P can be made continually

71
Q

fates for glucose-6P in liver

A

dephosphorylate to yield free glucose to go to other tissues

make into liver glycogen

enter glycolysis, make acetyl-CoA and then ATP for hepatocytes themselves

enter PPP to yield NADPH and ribose-5P

72
Q

metabolism of FA in liver

A

make lipids that contain fatty acids

break down FA into acetyl-CoA to make ATP

make acetyl-CoA into ketone bodies to be secreted for use in other organs

use acetyl-CoA to make sterols

secrete FA to be used in other organs

73
Q

in the liver: insulin stimulates ________ and inactivates

A

glycogen synthase and inactivates glycogen phosphorylase

UDP glucose —> glycogen

74
Q

in the liver glycolysis is stimulated

A

phosphofructokinase activated by inc. in fructose-2,6-bisphosphate (its allosteric regulator)

  • through dephosphorylation and activation of enzyme that makes it

pyruvate kinase activated by reversible covalent modification (phosphorylation)

75
Q

insulin stimulates

A

conversion of excess glucose to glycogen and/or triacylglycerol

76
Q

in muscle and adipose, insulin stimulates

A

glucose uptake (GLUT4) increases within plasma membrane

77
Q

muscles can store excess glucose as

A

glycogen

78
Q

in adipose, insulin stimulates

A

triacylglycerol synthesis and decreases triacylglycerol breakdown

79
Q

insulin changes transcription of more than 150 genes

A

inc: enzymes in glycolysis, PPP, lipid synthesis
dec: enzymes in gluconeogenesis

80
Q

glucagon role

A

acts in opposite to insulin

81
Q

glucagon goals

A

break down glycogen stores

increase gluconeogenesis in liver

release glucose into bloodstream

mobilize FA from fat for alt. energy source

produce ketone bodies for alt. energy source

82
Q

glucagon raises blood glucose and ketone bodies by

A

changes in liver metabolism

83
Q

glucagon: activates glycogen phosphorylase

A

inactivates glycogen synthase

glycogen —> glucose-1P —> glucose-6P —> glucose

84
Q

glucagon: promotes gluconeogenesis

A

stimualtes Fructose 1,6-bisphosphatase (inhibits glycolysis at phosphofructokinase-1) through allosteric regulation

inhibits pyruvate kinase by covalent modification

increases PEP carboxykinase — produces PEP from oxaloacetate

85
Q

effect of inhibiting pyruvate kinase by covalent modification

A

prevents PEP from being converted to acetyl-CoA

accumulation of phosphoenolpyruvate favors gluconeogenesis

86
Q

glucagon: inhibits acetyl-CoA carboxylase by covalent modification

A

decreases [malonyl-CoA] leading to increased ketone body formation

87
Q

glucagon affects adipose tissue to spare glucose for the brain

A

at adipose: activates triacylglycerol hydrolysis

activates hormone-sensitive lipase

results in FA transport to other tissues so that glucose is spared for the brain

88
Q

fuel use over 4 hours of human metabolism

A

immediately after a meal: glucose increases; insulin stimulates glycolysis, triacylglycerol synthesis, glycogen synthesis

2 or more hours: blood glucose drops; glucagon secreted, liver glycogen is broken down to glucose for other tissues

after 4 hours: more glucagon produced, triacylglycerol hydrolysis occurs, FA become fuel for muscle and liver

89
Q

effects of prolonged fasting

A

muscle used for fuel

liver deaminates or transaminates AA

FA oxidized to acetyl-CoA, but oxaloacetate is depleted to make glucose so ketone bodies formed and exported to other tissues

90
Q

liver deamination or transamination of AA

A

converts amino groups to urea

carbon skeletons of glucogenic amino acids converted to pyruvate, then glucose via gluconeogenesis

provides glucose for brain

MCB 3010 (12 decks)

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