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Block 3 > MMT: fatty acid oxidation > Flashcards

MMT: fatty acid oxidation Flashcards

1
Q

What are sources of fatty acids in the fed state?

A

Dietary TG and excess carbs

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2
Q

What are sources of fatty acids in the fasting state?

A

TG stored in lipid droplets

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3
Q

How are dietary TGs transported in the blood?

A

Chylomicrons

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4
Q

How are TGs formed from excess carbs transported in the blood?

A

VLDLs

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5
Q

How are TGs from lipid droplets transported in the blood?

A

Albumin, as fatty acids

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6
Q

For the most part, beta oxidation of fatty acids occurs with what type of chain fatty acids?

A

Long (C14-20)

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7
Q

What is the first step of fatty acid oxidation?

A

Activation via conversion to CoA derivatives

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8
Q

CoA derivatives (activated fatty acids) are transported to the mitochondria via…

A

The carnitine shuttle system

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9
Q

Describe the carnitine shuttle syndrome.

A
  1. Long chain fatty acyl CoA and esterified CoA enter through the outer mitochondrial membrane. 2. CPT I on the outer membrane replaces CoA with carnitine to esterify it. 3. Esterified carnitine and LC fatty acyl CoA enter the mitochondrial matrix. 4. CPT II on the inner membrane replaces carnitine with CoA, and allows LC fatty Acyl CoA and esterified CoA to be released into the mitochondrial matrix. 5. Carnitines translocate back into the intermembrane space.
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10
Q

What happens in each step of beta oxidation?

A

2 carbons are lost with a CoA group attached, forming acetyl CoA; this process repeats until 8 acetyl CoA are formed.

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11
Q

What is the four-reaction cycle of fatty acid beta oxidation?

A
  1. Oxidation (removing hydrogen). 2. Hydration (adding water). 3. Oxidation (removing hydrogen). 4. Thiolysis (cleavage).
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12
Q

Name the enzymes of beta-oxidation in order.

A
  1. Acyl CoA dehydrogenase. 2. Enoyl CoA dehydrogenase. 3. B-hydroxyacyl CoA dehydrogenase. 4. B-keto thiolase.
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13
Q

How are beta-oxidation and ETC linked?

A

The first enzyme in beta-oxidation (acyl-CoA dehydrogenase) is linked to the ETC complex.

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14
Q

What is a major control point of beta oxidation?

A

CPT-I

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15
Q

What inhibits CPT-I?

A

Malonyl-CoA

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16
Q

Describe CPT-I deficiency.

A

Causes an inability to use LC fatty acids for fuel, impairing the ability to make glucose when fasting.

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17
Q

CPT-I deficiency impacts which organ?

A

Liver

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18
Q

What does the diagnosis of CPT-I rely on?

A

Elevated free carnitine/acyl carnitine ratio.

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19
Q

What are clinical manifestations of CPT-I deficiency?

A

Hypoglycemia, coma, death, cardiomyopathy, rhabdomyolysis.

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20
Q

Describe CPT-II deficiency.

A

Causes an inability to release fatty acids for use in the mitochondrial matrix.

21
Q

What are clinical manifestations of CPT-II deficiency?

A

Muscle pain and myoglobinuria after exercise, hypoketotic hypoglycemia.

22
Q

How is CPT-II diagnosed?

A

High acyl carnitine/free carnitine ratio.

23
Q

What is the primary acyl CoA dehydrogenase used in the body?

A

Medium chain acyl CoA, though we start with VLCAD.

24
Q

Describe MCAD deficiency.

A

An autosomal recessive condition that results in people being ok until they’re not. After an excessive period of fasting or increased energy requirement, they’ll experience vomiting, lethargy, seizures, coma, and SUDI.

25
Q

What is the hallmark of MCAD deficiency?

A

Hypoketotic hypoglycemia.

26
Q

What is different about oxidation of unsaturated fatty acids?

A

The 1st reaction is skipped, resulting in one less FADH2 being produced overall.

27
Q

In an unsaturated fatty acid with 2 points of unsaturation, what is lost when compared to a saturated fatty acid of the same length? What about 1 point of unsaturation?

A

An FADH2 and an NADPH; one degree of saturation would result in one less FADH2.

28
Q

What is different about the products of odd chain FA oxidation?

A

Instead of 2 acetyl CoA, an acetyl CoA and propionyl CoA are produced in this last cycle.

29
Q

Oxidation of propionyl CoA produces…

A

Succinyl CoA.

30
Q

What coenzymes are needed to convert propionyl CoA to succinyl CoA?

A

Vitamin B12 and biotin.

31
Q

What is the major control point of beta oxidation of long chain FA?

A

CPTI

32
Q

What inhibits CPTI?

A

Malonyl CoA.

33
Q

When carbs convert to fats, what is the major control point?

A

Acetyl CoA carboxylase.

34
Q

Describe the role of acetyl CoA carboxylase in regulating FA oxidation in the fed state.

A
  1. High insulin leads to a phosphatase removing phosphate from ACC. 2. Activated ACC converts acetyl CoA to malonyl CoA. 3. Malonyl CoA inhibits CPTI, inhibiting oxidation and promoting synthesis.
35
Q

Describe the role of acetyl CoA carboxylase in regulating FA oxidation in the fasting state.

A
  1. Low ATP/high AMP increases AMPK. 2. AMPK phosphorylates ACC, inactivating it. 3. Malonyl CoA is not inhibited, so oxidation can occur.
36
Q

Where are very long chain FA oxidized?

A

Peroxisomes.

37
Q

How much ATP is formed via beta oxidation in peroxisomes?

A

None.

38
Q

In beta oxidation in peroxisomes, how do we replenish FAD?

A

By converting O2 to H2O2.

39
Q

What is the unique enzyme in beta oxidation in peroxisomes?

A

Acyl CoA oxidase as the first enzyme.

40
Q

What is X-linked adrenoleukodystrophy?

A

A disease caused by a deficiency in the transporter that brings very long chain fatty acids into peroxisomes. Results in accumulation of VLCFAs in the brain, adrenal cortex, testes, and liver.

41
Q

What gene is associated with X-linked adrenoleukodystrophy?

A

ABCD1.

42
Q

How do we confirm a diagnosis of X-linked adrenoleukodystrophy?

A

Elevated very long chain fatty acids in plasma.

43
Q

What is alpha oxidation?

A

Oxidation of branched fatty acids that is shifted by one carbon due to a group on the beta carbon; oxygen group is added to the alpha carbon instead of beta carbon.

44
Q

What enzymes are involved in alpha oxidation?

A
  1. Phytanoyl CoA synthase. 2. Phytanoyl CoA hydroxylase. 3. A-hydroxyphytanoyl CoA lyase. 4. Aldehyde dehydrogenase.
45
Q

What is Refsum’s disease?

A

A mutation in phytanoyl CoA enzyme in alpha oxidation results in a buildup of phytanic acid in brain, blood, and other tissues. Can cause night blindness, loss of smell, deafness, balance issues, peripheral neuropathy, heart issues.

46
Q

Where does omega oxidation occur?

A

ER.

47
Q

What is omega oxidation important for metabolizing?

A

Hydrophobic xenobiotics.

48
Q

What is special about the first enzyme in omega oxidation?

A

It is a CYP450 enzyme.

Block 3 (52 decks)

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