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biochem block 3 > fatty acid oxidation > Flashcards

fatty acid oxidation Flashcards

1
Q

number of carbons for:

short, medium, long, very long chain FA

A

short= 2-4
medium= 6-12
long= 14-20
very long= over 22

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2
Q

C present in most dietary and stored fats

A

16, 18

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3
Q

major pathway for b-oxidation occurs in the-

A

mitochondria

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4
Q

when is b-oxidation in the peroxisome needed?

A

b-oxidation in the peroxisome is an intermediate step that is needed for very long chain FA (22+ Carbons); this process will break FA into Medium chain length and then FA will enter mitochondria for completion

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5
Q

in b-oxidation, how are FA transported into the cell?

A

via fatty acid binding proteins

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6
Q

in b-oxidation, where/how are FA activated

A

in cytoplasm, acyl-CoA syntheses add CoA to activate FA using ATP

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7
Q

what is the location of acyl-CoA syntheses? why are there many isoforms?

A

located on the ER and outer mito membranes

many isoforms bc each is specific for one FA length

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8
Q

what FA use the carnitine shuttle?

A

Long chain

medium chain do not require

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9
Q

3 steps in the carnitine shuttle

A

1-CPT1 on outer mito membrane facing cytosol, transfers FA from CoA to OH of carnitine (forming acylcarnitine) and moving into inner membrane space
2- antiporter on the inner mito membrane mediates exchange of carnitine for acylcarnitine, now acylcarnitine in mito matrix
3- CPT2 in mito matrix transfers FA from carnitine back to CoA

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10
Q

what is the main control mechanism of FA oxidation? how?

A

carnitine shuttle

through regulation by malonyl-CoA

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11
Q

what forms malonyl-CoA? why is it formed?

A

malonyl-CoA is formed from acetyl-coA using acetyl-CoA carboxylase, in response to high acetyl-CoA

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12
Q

how does malonyl-CoA inhibit the carnitine shuttle?

A

malonyl-CoA inhibits CPT1

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13
Q

what is the end product of b-oxidation?

A

acetyl-CoA

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14
Q

what are the fates (3) of acetyl-CoA derived from b-oxidation?

A

in fed state- acetyl-CoA is oxidized in TCA cycle
in fasted state- acetyl-CoA is used to make ketone bodies in liver, in peripheral tissues ketone bodies are converted back to acetyl-CoA and are used for TCA cycle/energy

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15
Q

4 enzymes used in b-oxidation

A

1- acyl-CoA dehydrogenase
2- enoyl-CoA hydratase
3- b-hydroxyacyl-CoA dehydrogenase
4- acyl-coA acetyltransferase

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16
Q

describe the action of acyl-CoA dehydrogenase

A

makes C=C between a and B carbons, uses FAD+

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17
Q

describe the action of enoyl-CoA hydralase

A

adds H2O to add OH to B carbon

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18
Q

describe the action of b-hydroxyacyl-CoA dehydrogenase

A

removes H from OH on B carbon, to make C=O, uses NAD+

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19
Q

describe the action of acyl-CoA acetyl transferase

A

adds CoASH to make acyl-CoA + acetyl-CoA

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20
Q

what is unique about the acyl-coA dehydrogenase that is used for very long chain FA?

A

it is bound to the inner mito membrane, all others are soluble in mito matrix

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21
Q

what is contained in the “trifunctional protein complex”?

A

enoyl-CoA hydralase, b-hydroxyacyl-CoA dehydrogenase and acyl-CoA acetyltransferase for long chain FA; those for shorter chain FA are soluble in matrix

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22
Q

how many ATP are used in the activation process of FA?

A

2, one in the cytosol and 1 inside the mitochondria

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23
Q

describe regulation of b-oxidation by malonyl-coA

A

malonyl-CoA will decrease b-oxidation; malonyl-CoA is synthesized by acetyl-CoA carboxylase when acetyl-CoA levels are high, malonyl-CoA inhibits CPT1 and thereby decreases b-oxidation

24
Q

describe regulation of b-oxidation by insulin

A

insulin promotes FA synthesis by promoting the activity of acetyl-CoA carboxylase. Increased acetyl-CoA carboxylase activity will cause increased levels of malonyl-CoA that will inhibit CPT1 and decrease b-oxidation

25
Q

describe regulation of b-oxidation by energy charge

A

when ATP levels are high, ETC will slow. this will decrease the availability of NAD+ and thereby slows b-oxidation

26
Q

what is the main source of odd chain FA?

A

dietary in milk, comes from cow flora’s production of propionate that becomes incorporated into milk fats

27
Q

what is the result of b-oxidation of an odd chain FA?

A

final reaction will yield 1 acetyl-CoA and 1 propionyl-CoA

28
Q

what will happen to proprionyl-CoA after b-oxidation is complete?

A

in the liver, propionyl-CoA will be converted to succinyl-CoA that is then converted to oxaloacetate by the TCA cycle. Resulting oxaloacetate is then used for gluconeogenesis

29
Q

what is unique about b-oxidation of very long chain FA?

A

Very long chain (22+) must be converted to medium or short chain FA in peroxisomes before it can enter the mitochondria

30
Q

what do peroxisomes use for FA transport?

A

import- ABC transporters

export- carnitine shuttle

31
Q

what is unique about oxidation in perxisomes?

A

less energy is harnessed because FAD+ is used to form H2O2 (then broken down by catalase), NADH is generated and transferred to mitochondria, no ATP is directly made. Overall is less energentially favorable

32
Q

zellweger syndrome

A

lack of functional peroxisomes that causes an accumulation of FA C24-32

33
Q

X-linked adrenoleukodystrophy

A

specific defect in peroxisomal oxidation of VLCFA leading to their accumulation

34
Q

what is the purpose of a-oxidation?

A

for branched-chain FA-used when there is a methyl group present on the b-carbon, a-oxidation will remove the methyl group so that the compound can undergo b-oxidation

35
Q

where is a-oxidation?

A

in peroxisomes

36
Q

what is a common reaction that requires a-oxidation?

A

chlorophyll –> phytanic acid

37
Q

refsum disease

A

defective a-oxidation leads to accumulation of branched chain FA in the CNS, neurologic sx appear first

38
Q

what is the action of w-oxidation?

A

w-oxidation is a detox pathway that oxidizes the w-carbon to form a dicarboxylic acid that is more soluble and can be excreted

39
Q

what class of enzymes commonly use w-oxidation?

A

cytochrome P450

40
Q

medium chain acyl-CoA dehydrogenase deficiency

A

medium chain FA accumulate, will be converted to dicarboxylic acids by w-oxidation and excreted; m/c genetic disease related to FA catabolism, fasting and exercise will cause hypoketotic hypoglycemia

41
Q

2 types of ketone bodies

A

acetoacetate and b-hydroxybutarate

42
Q

what is the main ketone body in blood?

A

b-hydroxybutarate

43
Q

what enzyme is used to convert between the 2 types of ketone bodies?

A

b-hydroxybutarate dehydrogenase

44
Q

after how many days of fasting will ketone body levels plateau?

A

20

45
Q

what triggers the formation of ketone bodies?

A

during fasting, oxaloacetate is used up by gluconeogenesis and thus TCA cycle slows leading to accumulation of acetyl-CoA; acetyl-CoA present in liver mitochondria is used to make ketone bodies

46
Q

how are ketone bodies used for energy? (3)

A

b-hydroxybutarate –> acetoacetate –> acetoacyl-CoA –> 2 acetyl-CoAs

47
Q

what are the enzymes used for ketone body degradation?

A

1- b-hydroxybutarate dehydrogenase
2- succinyl-CoA/acetoacetate-CoA transferase
3- thiolase

48
Q

how does acetone form?

A

spontaneous decarboxylation of acetoacetate will form acetone

49
Q

why are children more prone to ketosis? (3)

A
  • use more energy per Kg mass
  • high higher brain to liver ratio
  • deplete glycogen stores more rapidly
50
Q

what is the m/c cause of ketosis in children?

A

infections that cause anorexia/vomiting

51
Q

what is the basis of a ketogenic diet?

A

3:1 lipid to carbohydrate calories

52
Q

2 diseases that can be helped with ketogenic diet

A

epilepsy (dec seziures)

pyruvate dehydrogenase def

53
Q

why are medium chain FA “more ketogenic”?

A

MCFA are more likely to be oxidized vs. stored OR be incorporated into membranes (overall- more likely to be used and not stored)

54
Q

hypoglycemia in the absence of increased ketone body formation suggests-

A

disease of FA transport/oxidation

55
Q

systemic carnitine deficiency

A

decreased carnitine will decrease carnitine shuttle and cause impaired use of long chain FA. deficiency is caused by defect in OCTN-2 leading to impaired reabsorption of carnitine from the kiddy and impaired accumulation of carnitine in mm, treat with carnitine and high carb/low fat diet

biochem block 3 (7 decks)

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