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Biochem BLOCK 2 > Fatty Acid Metabolism > Flashcards

Fatty Acid Metabolism Flashcards

1
Q

energy yield of completely oxidized FA to CO2 and water is…

A

9kcal/g

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2
Q

energy yield of protein and carb

A

4kcal/g

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3
Q

what is the energy yield for alcohol

A

7kcal/g

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4
Q

Acetyl CoA

A
  • NOT being used for making glucose

- used to make ketone bodies

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5
Q

adipose lipase

A

constitutive, low level release of FA from adipose, TAG–DAG + FA

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6
Q

Hormone-sensitive lipase (HSL)

A

has a major role in regulated TAG lipolysis and release of FA from adipose, TAG—DAG+FA

  • sensitive to epinephrine
  • trauma/stress, drop in glucose levels
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7
Q

lipoprotein lipase

A

releases FA from TAG in the circulating lipoproteins particles to free FA and glycerol (potentially a more complete release of FAs)

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8
Q

What is HSL phosphorylated and activated by?

A

cAMP dependent protein kinases

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9
Q

phosphorylation of HSL causes:

A
  • activates its enzymatic lipase activity
  • HSL binding to perilipin
  • fasting=phosphorylation
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10
Q

perilipin

A
  • lipid droplet surface protein

- phosphorylated HSL binds to it

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11
Q

hormone (epinephrine) mediated activation/phosphorylation of HSL to generate FA

A
  • epinephrine binds to GPCR indirectly activating adenylyl cyclase via Ga(s)
  • adenylyl cyclase generates cAMP
  • cAMP activates cAMP-dependent protein kinases
  • cAMP-dependent protein kinases phosphorylate HSL
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12
Q

hormone mediated deactivation of FA synthesis via phosphorylation of ACC

A
  • epinephrine binds to GPCR indirectly activating adenylyl cyclase via Ga(s)
  • adenylyl cyclase generates cAMP
  • cAMP activates cAMP-dependent protein kinases
  • cAMP-dependent protein kinases phosphorylate and deactivate acetyl CoA carboxylase (ACC)
  • carboxylation of acetyl CoA—melonyl CoA by acetyl coA carboxylase is inhibited
  • carbon to carbon condensation reactions inhibited
  • FA synthesis stops
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13
Q

insulin and HSL

A
  • insulin promotes dephospho rylation of HSL by activating phosphatase
  • This shuts off HSL catalyzed hydrolytic release of FA from TAG
  • won’t produce ACC
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14
Q

what do adipocytes lack?

A

glyverol kinase

cannot metabolize glycerol released in TAG degradation if all FAs are released from a TAG molecule

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15
Q

glycerol is:

A

-released into the blood and taken up by the liver
-phosphorylated in the liver to be used in TAG synthesis
OR
-reversibly converted to DHAP by glycerol phosphate dehydrogenase

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16
Q

DHAP

A

can participate in glycolysis or gluconeogensis

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17
Q

FA are taken up by cells and…

A

activated to CoA by fatty acyl CoA synthetase (thikinase)

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18
Q

what tissues do not use FA for energy?

A

brain and erythrocytes

  • erythrocytes have no mitochondria
  • not clear why brain doesn’t use them
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19
Q

what happens to 50% of free fatty acids released from adipose TA?

A

they are reesterified to glycerol 3-P. this process functions to decrease the plasma free FA level associated with insulin resistance in type 2 DM and obesity

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20
Q

what is the major pathway for obtaining energy from FA?

A

B-oxidation

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21
Q

B-oxidation occurs where?

A

mitpchondria

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22
Q

what form must the FA be in for B-oxidation?

A

fatty acyl CoA

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23
Q

what does B-oxidation involve?

A

successive removal of 2-carbon fragments removed from the carboxyl end

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24
Q

products of B-oxidation

A

acetly CoA, NADH, FADH2

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25
Q

transport of LCFA into the mitochondria

A
  • LCFAs enter a cell from the blood
  • LCFA CoA synthase (thiokinase) located on the cytosolic side of the mitochondria outer membrane and generates LCFA CoA in the cytosol
  • LCFA CoA CANNOT directly cross the inner membrane of the mitochondria due to the presence of the CoA
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26
Q

LCFA CoA synthase

A
  • thiokinase

- located on the cytosolic side of the mitochondrial outer membrane and generates LCFA CoA in the cytosol

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27
Q

LCFA CoA in regards to the inner membrane of the mitochdondria

A

-cannot cross due to the CoA

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28
Q

carnitine shuttle process

A
  • imports LCFAs into the mitochondria
  • long chain acyl groups require specialized transport into the mitochondria
  1. acyl groups are transferred from CoA to carnation by carnation acyl transferase-1 (CAT-1) on outer mitochondrial membrane enzyme
  2. acyl carnitine is transported into the mitochondrial matrix in exchange for free carnation bt carnation-acyl carnation translocase
  3. CAT-II on the matrix side of the inner mitochondrial membrane catalyzes acyl groups transfer from carnation to CoA
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29
Q

CAT-1

A
  • outer mitochondrial membrane enzyme

- transfers acyl groups from CoA to carnitine

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30
Q

carnitine -acyl carnitine translocase

A

transports acyl carnitine into the mitochondrial matrix in exchange for free carnitine

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31
Q

CAT-II

A
  • on the matrix side of the inner mitochondrial membrane

- catalyzes acyl group transfer from carnation to CoA

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32
Q

inhibitor of the carnation shuttle

A

-CAT-I inhibited by malonyl CoA

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33
Q

Cat-I inhibition

A
  • inhibited by malonyl CoA

- prevents LCFA transfer from CoA to carnitine

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34
Q

What does the inhibition of CAT-I by malonyl CoA prevent?

A
  • mitochondrial import and B-oxidation of newly synthesized LCFAs
  • B-oxidation of LCFAs to generate energy while in the well fed state
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35
Q

source of carnitine

A

obtained from diet or synthesized

  • primarily in meat products
  • synthesized by an enzymatic pathway in the liver and kidney using AA lysine and methionine
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36
Q

Where does 97% of carnitine reside in the body?

A

skeletal muscle

-must rely on uptake of synthesized and dietary sources from the blood

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37
Q

carnitine defficieny

A

reduces the ability of tissues to use LCFA as a metabolic fuel

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38
Q

secondary carnitine deficiencies

A

caused by

  • decreased synthesis due to liver disease
  • dietary malnutrition or a strict vegetarian diet
  • hemodialysis, which removes carnation
  • conditions when carnation requirements increase (pregnancy, severe infections, burns, trauma)
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39
Q

primary carnitine deficiencies

A

caused by congenital deficiencies in

  • renal tubular reabsorption of carnation
  • CAT-I or CAT-II function
  • treatment
    • avoid prolonged fasts, adopt a diet high in carbs and low in LCFA, supplement with MCFA and carnitine
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40
Q

CAT-I deficiency in primary carnitine deficiencies

A

decrease liver use of LCFA during a fast: severe hypoglycemia, coma, death

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41
Q

CAT-II genetic defect in primary carnation deficiencies

A

heart and skeletal muscle exhibits symptoms that range from cardiomyopathy to muscle weakness with myoglobinemia following prolonged exercise

42
Q

entry of short and medium chain FA into the mitochondira

A
  • FA ,12 carbons cross the inner mitochondrial membrane without carnitine or CAT-I/II systems
  • activated to CoA derivatives by thiokinases
43
Q

human milk

A

high in short/medium chain FA and not dependent on carnation or CAT-I to cross mitochondrial membrane.

44
Q

oxidation of MCFA

A

not regulated by malonyl CoA inhibitory affects on CAT-I

45
Q

B-oxidation of a fatty acyl CoA

A
  • 4 steps involving B-carbon
  • each round shortens the chain length by 2 carbons
  1. acyl CoA dehydrogenases: ox reaction producing FADH2
  2. enoyl CoA hydrolase: hydration step
  3. 3-hydroxyacyl CoA dehydrogenase: a second oxidation reaction produces NADH
  4. a thiolytic cleavage: releasing actely CoA
46
Q

How are the 4 steps repeated in B-oxidation of fatty acyl CoA?

A
  • repeated for saturated FA
  • repeated: (n-2)/2 for FA with even number of C
  • repeated (n-3)/2 for FA with odd number of C
47
Q

what is acetyl CoA a positive allosteric effector for?

A

pyruvate carboxylase linking FA oxidation and gluconeogenesis

48
Q

Energy yield from FA oxidation

A
  • energy yield from B-oxidation is high

- degrading 1 palimitoyl CoA (16C) to CO2 and H20 results in a net 129 ATP

49
Q

can CoA go to GNG?

A

no

50
Q

greatest flux through pathway in FA synthesis

A

after carbohydrate rich meal

51
Q

greatest flux through pathway in B-oxidation of FAs

A

in starvation

52
Q

hormonal state favoring pathway in FA synthesis

A

high insulin/glucagon ratio

53
Q

hormonal state favoring pathway in B-oxidation of FAs

A

low insulin/glucagon ratio

54
Q

major tissue site for FA synthesis

A

primarily liver

55
Q

major tissue site for B-oxidation

A

muscle, liver

56
Q

subcellular location of FA synthesis

A

primarily cytosol

57
Q

subcellular location of B-oxidation

A

primarily mitochondria

58
Q

carriers of acyl/acetyl groups between mitochondria and cytosol in FA synthesis

A

citrate (mitochondria to cytosol)

59
Q

carriers of acyl/acetyl groups between mitochondria and cytosol in B-oxidation

A

carnitine (cytosol to mitochondria)

60
Q

Phosphopantetheine-containing active carriers in FA synthesis

A

acyl carrier protein domain, CoA

61
Q

Phosphopantetheine-containing active carriers in B-oxidation

A

CoA

62
Q

oxidation/reduction coenzymes in FA synthesis

A

NADPH (reduction)

63
Q

oxidation/reduction coenzymes in B-oxidation

A

NAD+, FAD (oxidation)

64
Q

two carbon donor/product of FA synthesis

A

malonyl CoA: donor of one acetyl group

65
Q

oxidation/reduction coenzymes in B-oxidation

A

acetyl CoA; product of B-ox

66
Q

activator of FA synthesis

A

citrate

67
Q

inhibitor of FA synthesis

A

-long chain fatty acyl CoA (inhibits acetyl CoA carboxylase)

68
Q

inhibitor in B-oxidation

A

malonyl CoA (inhibits carnitine palmitoyltransferase-I)

69
Q

product of FA synthesis

A

palmitate

70
Q

Product of B-oxidation

A

Acetyl CoA

71
Q

repetetive 4 step process in FA synthesis

A
  • condensation, reduction

- dehydration, reduction

72
Q

repetetive 4 step process of B-oxidation

A
  • dehydrogenation, hydration

- dehydrogenation, thiolysis

73
Q

B-oxidation o FA with an odd number of C

A

similar to that of even number of carbons with the exception that the final thiolytic cleavage produces a 3-C product: propionyl CoA

74
Q

What is the product of B-oxidation of a FA with an odd number of C?

A

propionyl CoA

75
Q

How is Propionyl CoA metabolized?

A
  1. synthesis of D-methylmalonyl CoA: propionyl CoA is carboxylated by propionyl CoA carboxylase
  2. formation of L-methylmalonyl CoA: D to L-methylmalonyl CoA isomer conversion by methylmalonyl CoA racemase
  3. synthesis of saucily CoA: the carbon of L-methylmalonyl CoA are rearranged to form saucily CoA by methylmalonyl CoA mutters: saucily CoA enters the TCA cycle
76
Q

What is the end product of B oxidation of a FA with an odd number of carbons

A

succinyl CoA

77
Q

Vitamin B12 deficiency in FA

A
  • causes excretion of both propionate and methylmalonate in the urine
  • heritable methylmalonic acidemia OR aciduria is possible
  • both result in metabolic acidosis, potential for developmental retardation
78
Q

B oxidation in the peroxisome

A
  • VLCFA are initially oxidized in the peroxisome

- peroxisomal B-oxidation does not generate ATP

79
Q

Zellwegger syndrome

A

a peroxisome biogensis disorder

  • genetic defects that result in failure to target matrix proteins
  • Cause the accumulation of VLCFA in the blood and tissues
80
Q

X-linked adrenoleukodystrophy

A
  • genetic defects causing the failure to transport VLCFA across the peroxisomal membrane.
  • disconnect in sensing environment
  • Cause the accumulation of VLCFA in the blood and tissues
81
Q

a-oxidation of FA

A
  • branched-chain, 20-C FA phytanic acid cannot function as a substrate for acetyl CoA dehydrogenase due to the methyl group at its B-carbon
  • paytanoyl CoA a-hydroxylase (PhyH) hydroxylates the a-carbon and carbon 1 is released as CO2
  • 19 carbon pristanic acid is activated to CoA and undergoes B-oxidation
82
Q

Refsum disease

A
  • rare, autosomal, recessive: caused by peroxisomal PhyH deficiency
  • phytanic acid accumulates in the blood and tissues
  • symptoms are primarily neurologic
  • treatment requires dietary restrictions to halt disease progression
83
Q

medium chain fat acyl CoA dehydrogenase deficiency

A
  • decreased oxidation of 6- to 10- carbon FA
  • medium chain length FA accumulate; can be measured in the urine
  • avoid fasting
  • one of the most common inborn errors of metabolism
  • the most common inborn error of FA oxidation
84
Q

what is the most common inborn error of FA metabolism/oxidation?

A

MCAD deficiency

85
Q

Ketone bodies

A
  • soluble in aqueous solution (no lipoprotein or albumin transport required)
  • produced in liver when acetyl CoA levels supersede oxidation capacity
  • use is proportional to concentration in the blood by:
    • extra-hepatic tissues such as heart, skeletal muscle, and renal cortex
    • brain can utilize ketone bodies for energy source if levels are sufficient
86
Q

Why are ketone bodies important during fasting?

A

ketone bodies decrease the demand on blood glucose

87
Q

hypoketosis

A

due to decreased acetyl CoA availability

88
Q

hypoglycemia

A

due to increased reliance on glucose for energy

89
Q

ketogensis

A
  • during fast
  • FA accumulates in liver
  • increased hepatic acetyl CoA
  • OAA used fir GNG (not used in TCA cycle)–acetly CoA is channeled into ketone body synthesis
  • FA oxidation decreases the NAD+:NADH ratio and the increased NADH shifts the OAA to malate
  • formation of malate shifts acetyl CoA away from GNG, toward ketogenesis
90
Q

what does increase hepatic CoA do?

A
  • inhibitis pyruvate dehydrogenase

- activates pyruvate carboxylase…OAA is produced

91
Q

synthesis of HMG CoA: formation of acetoacetyl CoA

A

-reversal of the thiokinase reaction of FA oxidation step 4

92
Q

synthesis of HMG CoA: HMG CoA synthase

A
  • combines a third molecule of acetyl CoA with acetoacyl CoA to generate HMG CoA
  • HMG CoA synthase is the rate limiting step in ketone body synthesis and it present only in the liver to significant amounts
93
Q

synthesis of HMG CoA: HMG cleavage

A

HMG CoA cleaved to produce acetoacetate and acetyl CoA

94
Q

synthesis of HMG CoA: reduction of acetoacetate

A

acetoacetate can be reduced to 3-hydroxybutyrate with NADH as the hydrogen donor

95
Q

synthesis of HMG CoA: formation of acetone

A
  • acetoacetate can spontaneously decarboxylate to form acetone in the blood
  • acetone is a volatile, biologically non metabolizes compound that is released in the breath
96
Q

ketone bodies in peripheral tissues

A

3-hydroxybutyrate is oxidized to acetoacetate by 3-hydroxy butyrate dehydrogenase, producing NADH in peripheral tissues

97
Q

What happens in peripheral tissues when 3-hydroxybutyrate is oxidized to avetoacetate?

A
  • acetoacetate is then provided with a CoA molecule taken from saucily CoA by saucily CoA: acetoacetate CoA transferase (thiophorase)
  • acetoacetyl CoA is converted to (2) acetyl CoA and goes to TCA
98
Q

Can liver use ketone bodies?>

A

no, it lacks thiophorase

99
Q

excess of ketone bodies in DM

A
  • ketonemia (ketone rise in blood)

- KEtonuria (ketone rise in urine)

100
Q

diabetic ketoacidosis

A
  • fruity breath from acetone
  • increased ketone bodies and glucose
  • decreased blood volume increases H+ concentration causing severe acidosis
  • can be caused by fasting

Biochem BLOCK 2 (14 decks)

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