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Harpers - Biochemistry > Ch 22 - Oxidation Of Fatty Acids: Ketogenesis > Flashcards

Ch 22 - Oxidation Of Fatty Acids: Ketogenesis Flashcards

1
Q

Each step in fatty acid oxidation involves _______________, is catalyzed by separate enzymes, utilizes ____ and _____ as coenzymes, and generates ATP.

A

Acyl-CoA derivatives

NAD+ and FAD

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2
Q

It is an aerobic process, requiring the presence of oxygen.

A

Fatty acid oxidation

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3
Q

_____________ is a characteristic of starvation and of diabetes mellitus and leads to increased ketone body production by the liver (ketosis).

A

Increased fatty oxidation

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4
Q

Because gluconeogenesis is dependent upon fatty acid oxidation, any impairment in fatty acid oxidation leads to _________.

A

Hypoglycemia

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5
Q

This occurs in various states of CARNITINE DEFICIENCY, or deficiency of essential enzymes in fatty acid oxidation, for example _______________ or inhibtion of fatty acid oxidation by poisons, for example ___________.

A

Carnitine palmitoyltransferase

Hypoglycin

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6
Q

Oxidation of fatty acids occurs in ___________.

A

Mitochondria

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7
Q

Fatty acids are transported in the blood as ______________.

A

Free fatty acids

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8
Q

Free fatty acids (FFAs) also called __________ or _________ are fatty acids that are in the UNESTERIFIED STATE.

A

Unesterified (UFA) or nonesterified (NEFA) fatty acids

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9
Q

In plasma, longer chain FFA are combined with _______ and in the cell they are attached to a FATTY ACID BINDING PROTEIN so that in fact they are never really “free”.

A

Albumin

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10
Q

____________ are more WATER-SOLUBLE and exist as the UNIONIZED ACID or as a FATTY ACID ANION.

A

Shorter chain fatty acids

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11
Q

Fatty acids are activated before being _________.

A

Catabolized

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12
Q

True or False:

Fatty acids must be first converted to an active intermediate before they can be catabolized.

A

True

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13
Q

This is the only step in the complete degradation of a fatty acid that requires energy from ATP.

A

Fatty acids are activated before being catabolized

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14
Q

In the presence of ATP and coenzyme A, the enzyme ____________ catalyzes the conversion of a fatty acid to an “active fatty acid” or ____________ using one high-energy phosphate and forming AMP and PPi.

A

Acyl-coA synthetase (thiokinase)

Acyl-CoA

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15
Q

The PPi is hydrolyzed by ___________ with the loss of a further high-energy phosphate ensuring that the overall reaction goes to completion

A

Inorganic pyrophosphatase

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16
Q

Found in the endoplasmic reticulum, peroxisomes and inside and on the outer membrane of mitochondria

A

Acyl-CoA synthetases

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17
Q

Long-chain fatty acids penetrate the inner mitochondrial membrane as _____________.

A

Carnitine derivatives

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18
Q

Is widely distributed and is particularly abundant in muscle.

A

Carnitine (B-hydroxy-y-trimethylammonium butyrate)

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19
Q

True or False: Long-chain acyl-CoA cannot penetrate the inner membrane of mitochondria.

A

True

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20
Q

Located in the outer mitochondrial membrane, transfers long-chain acyl group from CoA to carnitine forming __________ and releasing CoA.

A

Carnitine palmitoyltransferase-I

Acylcarnitine

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21
Q

Acylcarnitine is able to penetrate the inner membrane and gain access to the B-oxidation system of enzymes via the inner membrane exchange transporter _________________.

A

Carnitine-acylcarnitine translocase

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22
Q

The acyl group is then transferred to CoA so that acyl-CoA is reformed and carnitine is liberated. This reaction is catalyzed by ____________ which is located on the inside of the inner membrane

A

Carnitine palmitoyltransferase II

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23
Q

In the ____________, two carbons at a time are cleaved from acyl-CoA molecules starting at the CARBOXYL END.

A

B-oxidation pathway

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24
Q

The two-carbon units formed are acetyl-CoA thus __________ forms eight acetyl-CoA molecules.

A

Palmitoyl-CoA

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25
Q

The B-oxidation cycle generates ________ and _______.

A

FADH2 and NADH

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26
Q

Several enzymes known collectively as __________ are found in the mitochondrial matrix or inner membrane adjacent to the respiratory chain.

A

Fatty acid oxidase

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27
Q

In the process, large quantities of the reducing equivalents FADH2 and NADH are generated and are used to form ATP by _____________.

A

Oxidative phosphorylation

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28
Q

The first step is the removal of TWO hydrogen atoms from the 2(a) and 3(b) carbon atoms, catalyzed by __________ and requiring ______. This results in the formation of 🔼2-trans-enoyl-CoA and FAD.

A

Acyl-CoA dehydrogenase

FAD

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29
Q

The reoxidation of FADH2 by the respiratory chain requires the meditation of another flavoprotein termed _____________.

A

Electron-transferring flavoprotein

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30
Q

Water is added to saturate the double bond and form 3-hydroxy-acyl-CoA, catalyzed by _______________.

A

🔼2-enoyl-CoA hydratase

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31
Q

The 3-hydroxy derivative undergoes further dehydrogenation on the 3-carbon cataylzed by _______________ to form the corresponding 3-ketoacyl-CoA compound. In this case, _____ is the coenzyme involved.

A

L (+) - 3-hydroxyacyl-CoA dehydrogenase

NAD+

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32
Q

Finally, 3-ketoacyl-CoA is split at the 2,3-position by _________ forming acetyl-CoA and a new acyl-CoA two carbons shorter than the original acyl-CoA molecule.

A

Thiolase (3-ketoacyl-CoA-thiolase)

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33
Q

The shorter acyl-CoA formed in the cleavage reenters the oxidative pathway at __________.

A

Reaction 2

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34
Q

For example, after SEVEN cycles the C16 fatty acid, _________ would be converted to eight acetyl CoA molecules.

A

Palmitate

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35
Q

Since acetyl-CoA can be oxidized to CO2 and water via the ______________, the complete oxidation of fatty acids is achieved.

A

Citric acid cycle

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36
Q

Oxidation of a fatty acid with an ODD NUMBER of carbon atoms yields ACETYL-CoA plus a molecule of ___________.

A

Propionyl-CoA

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37
Q

Fatty acids with an odd number of carbon atoms are oxidized by the pathway of B-oxidation described above producing acetyl CoA until a three-carbon __________ residue remains.

A

Propionyl-CoA

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38
Q

This compound is converted to __________, a consistuent of the citric acid cycle.

A

Succinyl-CoA

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39
Q

Hence, the propionyl residue from an odd-chain fatty acid is the only part of a fatty acid that is _________.

A

Glucogenic

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40
Q

Oxidation of fatty acids produces a large quantity of ______.

A

ATP

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41
Q

Transport of electrons from FADH2 and NADH via the respiratory chain leads to the synthesis of ____ high-energy phosphates for each of the seven cycles needed for the breakdown of the C16 fatty acid, palmitate to acetyl-CoA. (7 x 4 = 28)

A

4

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42
Q

A total of ___ mol of acetyl-CoA is formed and each gives rise to ___ mol of ATP on oxidation in the CTA making ___ mol.

A

8
10
80

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43
Q

Two must be substracted for the initial activation of the fatty acid, yielding a net gain of ____ mol of ATP per mole of palmitate or 106 x 30.5 = 3233 kJ. This represents ___% of the free energy of combustion of palmitic acid.

A

106 mol

33%

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44
Q

_______ oxidize very long chain fatty acids.

A

Peroxisomes

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45
Q

A modified form of B-oxidation is found in _______ and leads to the formation of acetyl-CoA and H2O2 (from the flavoprotein-linked dehydrogenase step), which is broken down by ______.

A

Peroxisomes

Catalase

46
Q

True or False:

Thus, the dehydrogenation in peroxisomes is not linked directly to phosphorylation and the generation of ATP.

A

True

47
Q

The system facilitates the oxidation of VERY LONG CHAIN FATTY ACIDS. The enzymes responsible are induced by high-fat diets and in some species by hypolipidemic drugs such as _________.

A

Clofibrate

48
Q

The enzymes in peroxisomes do not attack shorter chain fatty acids; the B-oxidation sequence ends at __________.

A

Octanoyl-CoA

49
Q

Octanoyl and acetyl groups are both further oxidized in ____________.

A

Mitochondria

50
Q

Another role of peroxisomal B-oxidation is to _______ the side chain of cholesterol in bile acid formation.

A

Shorten

51
Q

__________ also take part in the synthesis of ETHER GYLCEROLIPIDS, CHOLESTEROL and DOLICHOL.

A

Peroxisomes

52
Q

Oxidatiom of unsaturated fatty acids occurs by a _______________.

A

Modified B-oxidation pathway

53
Q

The CoA esters of unsaturated fatty acids are degraded by the enzymes normally responsible for B-oxidation until either a ______________ compound or a _____________ compound is formed, depending upon the position of the double bonds.

A

🔼3-cis-acyl-CoA or 🔼4-cis-acyl-CoA compound

54
Q

The former compound is isomerized _________________ to the corresponding 🔼2-trans-CoA stage of B-oxidation for subsequent hydration and oxidation.

A

🔼3cis -> 🔼2-trans-enoyl-CoA isomerase

55
Q

____________ occurs when there is a high rate of fatty-acid oxidation in the liver.

A

Ketogenesis

56
Q

Under merabolic conditions associated with a high rate of fatty acid oxidation, the liver produces considerable quantities of _______ and _________.

A

Acetoacetate and D(–)-3-hydroxybutyrate (B-hydroxybutyrate)

57
Q

Acetoacetate continually undergoes spontaneous decarboxylation to yield ____________.

A

Acetone

58
Q

Acetoacetate and 3-hydroxybutyrate are interconverted by the mitochondrial enzyme ________________; the equilibrium is controlled by the mitochondrial [NAD+]/[NADH] ratio, that is the ____________.

A

D(-)-3-hydroxybutyrate dehydrogenase

59
Q

The concentration of total ketone bodies in the blood of well-fed mammals does not normally exceed ____ mmol/L except in ruminants, where 3-hydroxybutyrate is formed continously from _________ (a product of ruminal fermentation) in the rumen wall.

A

0.2 mmol/L

Butyric acid

60
Q

In vivo, _____ appears to be the only organ in nonruminants to add significant quantities of ketone bodies to th blood.

A

Liver

61
Q

Extrahepatic tissues utilize acetoacetate and B-hydroxybutyrate as ______________.

A

Respiratory substrates

62
Q

________ is a waste product which, as it is VOLATILE, can be excreted via the lungs.

A

Acetone

63
Q

True or False:

Because there is active synthesis but LITTLE UTILIZATION of ketone bodies in the liver, while they are used but not produced in extrahepatic tissues, there is a net flow of the compounds to the extrahepatic tissues.

A

True

64
Q

________________ is an intermediate in the pathway of ketogenesis.

A

3-hydroxy-3-methylglutaryl-CoA (HMG-CoA)

65
Q

Enzymes responsible for ketone body formation are associated mainly with the _________.

A

Mitochondria

66
Q

The term ketones should not be used as there are ketones in blood that are not ketone bodies, for example, __________ and _________.

A

Pyruvate and fructose

67
Q

Two acetyl-CoA molecules formed in B-oxidation condense to form acetoacetyl-CoA by a reversal of the __________ reaction.

A

Thiolase

68
Q

___________, which is a starting material for ketogenesis, also arises directly from the terminal FOUR carbons of a fatty acid during B-oxidation.

A

Acetoacetyl-CoA

69
Q

Condensatiom of acetoacetyl-CoA with another molecule of acetyl-CoA by _________________ forms 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA).

A

3-hydroxy-3-methylglutaryl-CoA synthase

70
Q

______________ then causes acetyl-CoA to split off from the HMG-CoA, leaving free aceto-acetate.

A

3-hydroxy-3-methylglutaryl-CoA lyase

71
Q

True or False:

BOTH ENZYMES must be present in mitochondria for ketogenesis to take place.

A

True

72
Q

____________ is quantitatively the predominant ketone body present in the blood and urine in ketosis

A

D(-)-3-hydroxybutyrate

73
Q

Serve as a fuel for extrahepatic tissues.

A

Ketone bodies

74
Q

Acetoacetat once formed cannot be reactivated directly except in the _________, where it is used in a much less active pathwat as a precursor in cholesterol synthesis.

A

Cytosol

75
Q

In extrahepatic tissues, acetoacetate is activated to acetoacetyl-CoA by ___________________.

A

Succinyl-CoA-acetoacetate CoA transferase

76
Q

With the addition of CoA, the acetoacetyl-CoA is split into two acetyl-CoAs by _________ and oxidized in the citric acid cycle.

A

Thiolase

77
Q

If the blood level is raised, oxidation of ketone bodies increases until, at a concentration of ~____ mmol/L, the oxidative machinery is saturated.

A

12 mmol/L

78
Q

Is due to increased production of ketone bodies by the liver rather than to a deficiency in their utilization by extrahepatic tissues.

A

Ketonemia

79
Q

Is difficult to oxidixe IN VIVO and to a large extent is volatilized in the lungs.

A

Acetone

80
Q

In ____________, the loss of ketone bodies via the urine is only a few percent of the total ketone body production and utilization.

A

Moderate ketonemia

81
Q

Measurement of the ________, not the ketonuria, is the preferred method of assesing the severity of ketosis.

A

Ketonemia

82
Q

Ketosis does not occur in vivo unless there is an increase in the level of circulating ______ that arise from lipolysis of triacylglycerol in adipose tissue.

A

FFAs

83
Q

Are the precursors of ketone bosies in the liver.

A

FFAs

84
Q

The liver, both in fed and in fasting conditions, extracts ~__% of the FFAs passing through it, so that a high concentrations the flux passing into the liver is substantial.

A

30%

85
Q

Therefore, the factors regulating ______________ from adipose tissue are important in controlling ketogenesis.

A

Mobilization of FFA

86
Q

After uptake by the liver, FFAs are either _________ to CO2 or ketone bodies or ___________ to triacylglycerol and phospholipid.

A

B-oxidized

Esterified

87
Q

There is regulation of entry of fatty acids into th oxidative pathway by _______________ and the remainder of the fatty acid taken up is eterified.

A

Carnitine palmitoyltransferase-I (CPT-I)

88
Q

CPT-I activity is ____ in the fed state, leading to depression of fatty acid oxidation and ____ in starvation, allowing fatty acid oxidation to increase.

A

Low

High

89
Q

____________ the initial intermediate in fatty acid biosynthesis formed by acetyl-CoA carboxylase in the fed state, is a potent inhibitor of CPT-I.

A

Malonyl-CoA

90
Q

FFA enter the liver cell in low concentrations and are nearly all esterified to acylglycerols and transported out of the liver in _______.

A

VLDL

91
Q

These events are reinforced in starvation by a decrease in ____________.

A

Insulin/glucagon ratio

92
Q

Impaired oxidation of fatty acids gives rise to disease often associated with _____________.

A

Hypoglycemia

93
Q

A fall in the concentration of _____________, particularly within the mitochondria, can impair the ability of the citric acid cycle to metabolize acetyl-CoA and divert fatty acid oxidation toward ketogenesis.

A

oxaloacetate

94
Q

_______________ can occur particularly in the newborn— and especially in preterm infants—owing to inadequate biosynthesis or renal leakage.

A

Carnitine deficiency

95
Q

Symptoms of deficiency include __________, which is a consequence of impaired fatty acid oxidation and lipid accumulation with muscular weakness.

A

hypoglycemia

96
Q

______________ affects only the liver, resulting in reduced fatty acid oxidation and ketogenesis, with hypoglycemia.

A

Inherited CPT-I deficiency

97
Q

_________________ affects primarily skeletal muscle and, when severe, the liver

A

CPT-II deficiency

98
Q

The sulfonylurea drugs (_____________________), used in the treatment of type 2 diabetes mellitus, reduce fatty acid oxidation and, therefore, hyperglycemia by inhibiting CPT-I.

A

glyburide [glibenclamide] and tolbutamide

99
Q

Inherited defects in the enzymes of β-oxidation and ketogenesis also lead to _____________, _______________ and _____________.

A

nonketotic hypoglycemia, coma, and fatty liver.

100
Q

Defects are known in long-and short-chain 3-hydroxyacyl-CoA dehydrogenase (deficiency of the long-chain enzyme may be a cause of __________________).

A

acute fatty liver of pregnancy

101
Q

3-KetoacylCoA thiolase and HMG-CoA lyase deficiency also affect the degradation of ___________, a ketogenic amino acid.

A

leucine

102
Q

Jamaican vomiting sickness is caused by eating the unripe fruit of the akee tree, which contains the toxin _____________.

A

hypoglycin

103
Q

This inactivates medium- and short-chain acyl-CoA dehydrogenase, inhibiting β-oxidation and causing hypoglycemia.

A

Jamaican vomitting disease

104
Q

________________ is characterized by the excretion of C6´C10 ω-dicarboxylic acids and by nonketotic hypoglycemia, and is caused by a lack of mitochondrial medium-chain acyl-CoA dehydrogenase.

A

Dicarboxylic aciduria

105
Q

______________ is a rare neurologic disorder due to a metabolic defect that results in the accumulation of phytanic acid, which is found in dairy products and ruminant fat and meat.

A

Refsum disease

106
Q

___________ is thought to have pathological effects on membrane function, protein prenylation, and gene expression.

A

Phytanic acid

107
Q

__________________ occurs in individuals with a rare inherited absence of peroxisomes in all tissues. They accumulate C26´C38 polyenoic acids in brain tissue and also exhibit a generalized loss of peroxisomal functions. The disease causes severe neurological symptoms, and most patients die in the first year of life.

A

Zellweger (cerebrohepatorenal) syndrome

108
Q

The basic form of ketosis occurs in ___________ and involves depletion of available carbohydrate coupled with mobilization of FFA.

A

starvation

109
Q

_________________ of ketosis are found under conditions of high-fat feeding and after severe exercise in the postabsorptive state.

A

Nonpathologic forms

110
Q

Acetoacetic and 3-hydroxybutyric acids are both _____________ and are buffered when present in blood or other tissues.

A

moderately strong acids

Harpers - Biochemistry (5 decks)

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