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MSK Week 3 > 2.3.4. Oxidation of Fatty Acids > Flashcards

2.3.4. Oxidation of Fatty Acids Flashcards

1
Q

How do Fatty Acids (FA) travel in the bloodstream?

A

They travel bound to Albumin (a common protein) due to their hydrophobicity. They may also be bound to other things which have “room” for them.

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2
Q

What do our bodies use fat for? (Think metabolically)

A

Fat is a source of energy, so it is a fuel

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3
Q

How do we classify FAs?

A

We classify them by chain length

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4
Q

What are the classficiations of FAs?

A

Very long chain

Long Chain

Medium chain

Short chain

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5
Q

How many carbons are in each of the classifications of FAs?

1) Very Long Chain
2) Long Chain
3) Medium Chain
4) Short Chain

A
  1. >20 carbons
  2. 12-20 carbons
  3. 6-12 carbons
  4. <6 carbons
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6
Q

What do the greek letters tell you about chemical structures?

A

The greek letters tell you the location of carbon atoms in a chain relative to the number one, or most oxidized, carbon of the chemical structure.

The alpha carbon is one carbon away from the carbon labeled “1”, the beta is two away, and the omega is the last carbon of the chain, furthest from the number one carbon

Recall the phrase “I am the alpha and the omega” means “I am the beginning and the end”

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7
Q

What does the term omega-3 or omega-6 mean?

A

This terminology tells you where the final double bond lies in an unsaturated FA. If it is omega-3, then the double bond involves the third to final carbon of the FA. Omega-6 means it involves the sixth to final carbon.

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8
Q

What does the Δ tell you in FA nomenclature?

A

The Δ tells you the locations of the double bonds within the FA.

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9
Q

How many double bonds, and where are they, does a FA with Δ9,12,15 have?

A

It has three double bonds, which start at the 9th, 12th, and 15th carbons

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10
Q

What does the writing C16:0 mean?

A

This is a fatty acid with 16 carbons (16C) and 0 double bonds (:0)

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11
Q

What is the structure of palmitate and its short hand?

A

C16:0

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12
Q

What is the chemical structure for Stearate and its shorthand?

A

C18:0

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13
Q

What is the chemical structure for Oleate and its shorthand?

A

C18:1Δ9

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14
Q

What is the chemical structure for linoleate and its shorthand?

A

C18:2Δ9,12

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15
Q

How does having double bonds in the middle of the FA chain affect FA stacking?

A

Saturated (no double bonds) FAs can stack well on top of each other, but when a cis double bond gets put into the FA, it screws the stacking up by kinking the chain at an angle. Double bonds in the middle of the FA chain have the greatest effect on stacking.

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16
Q

What does the term free fatty acid (FFA) refer to?

A

It refers to unesterified FAs, or ones that have not been attached to glycerol quite yet.

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17
Q

In order to undergo degradation, what do Long Chain FAs (LCFAs) need to enter the mitochondria?

A

They need to be transported, and this is done through carnitine dependent transport.

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18
Q

What happens when LCFAs cannot enter the mitochondria because of a deficiency in or lack of carnitine transport?

A

Cannot degrade LCFAs, they build up (toxic to the cell)

Causes weakness, hypotonia, and hypoketotic hypoglycemia (low levels of ketone bodies and suger in the blood)

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19
Q

What will a deficiency in Acyl-CoA dehydrogenase do to your body?

A

A deficiency in Acyl-CoA dehydrogenase will result in increased dicarboxylic acids and decreased glucose and ketones

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20
Q

What will happen in the case of decreased Acetyl-CoA and why?

A

A decrease in Acetyl CoA, a (+) allosteric regulator of pyruvate carboxylase in gluconeogenesis, results in decreased glucose

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21
Q

What are fat cells specialized to do?

A

To hold fat, especially in the form of triacylglycerols (TGs).

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22
Q

Why is fat a better source of energy than glycogen (in terms of calories obtained/gram weight?

A

Two reasons:

1) Fat is more reduced than glycogen

Carbohydrates = 4 cal/g

Fat = 9 cal/g

2) Fat does not bind water, so it is lighter than glycogen (which binds 4 g H2O/gram glycogen)

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23
Q

How are TGs transported around the body?

A

Through specialized vesicles known as chylomicrons.

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24
Q

How are FFAs transported around the body?

A

Through binding to Albumin

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25
Q

What are the three possible fates for FA-CoA (FA bound to CoA) in the body?

A

1) Beta oxidation, maybe ketogenesis (energy)
2) TGs (storage)
3) Phospholipids and sphingolipids (membrane synthesis)

26
Q

How are FAs transported into the mitochondria?

A

Through the acylcarnitine transport chain system

27
Q

What are the steps of the acylcarnitine transport system?

A

1) Attach FA to CoA (acyl CoA Synthetase)
2) FA-CoA enters intermembrane space
3) FA-CoA exchanges CoA for carnitine (Carnitine palmitoyl transferase I)
4) Transfer to mito matric via carnitine-acylcarnitine translocase
5) Exchange of carnitine for CoA via Carnitine palmitoyl transferase II (CPT II)

28
Q

How is the FA carnitine transport system regulated?

A

Regulated via CPT I (carnitine palmitoyl transferase I)

29
Q

What kind of molecule is carnitine?

A

It is a zwitterionic alcohol

Multiple charges that negate each other overall

Hydroxyl group

30
Q

In beta oxidation of fatty acids, what are we doing to the fatty acids?

A

We are breaking them down via dehydrogenation

31
Q

What are the steps to beta oxidation of FAs?

A

Repeat until you have no more FA!

32
Q

What problems might arise when unsaturated FAs attempt to undergo beta oxidation?

A

May create an intermediate with the C=C in the wrong place (C3-C4 vs C2-C3)

Cis-double bonds are not recognized by enoyl CoA hydratase

May create an intermediate with a conjugated double bond

Additional enzymes are required: Enoyl CoA isomerase and 2,4-dienoyl reductase (uses NADPH)

33
Q

What is the energy yield, in terms of ATP, we get from each NADH and FADH2 from beta oxidation?

A

NADH = 2.5

FADH2 = 1.5

Same as TCA!

34
Q

How many NADH and FADH2 do you get for each pair of carbons removed via beta oxidation?

A

1 FADH2, 1 NADH

35
Q

How many FADH2’s and NADH’s do we get from undergoing complete beta oxidation of palmitate?

(Hint: C16:0)

A

From 16 carbons, 8 acetyl-coAs can be made, which requires 7 run throughs of beta oxidation, meaning:

7 FADH2 and 7 NADH2

36
Q

If we get 8 FADH2 and 8 NADH from beta oxidation, how many ATPs does that generate?

A

8 x 2.5 (NADH) = 20

8 x 1.5 (FADH2) = 12

Total = 32!

37
Q

For naturally occurring unsaturated FAs, what are the two extra steps we must undergo?

A

1) enoyl CoA isomerase isomerizes a cis double bond to a trans (once beta oxidation hits the cis bond)
2) 2,4-Dienoyl CoA Reductase takes the conjugated double bonds from carbons 2 and 4 and converts them to a single trans bond at carbon 3

This carbon 3 double bond is then isomerized by enoyl CoA Isomerase (from above) to a carbon 2 double bond

38
Q

How is beta oxidation regulated?

A

Two things:

1) NAD+/NADH ratio
2) Compartmentalization:

FA oxidation is located in the mitochondrial matrix

FA synthesis is located in the cytosol

Carnitine transport system blocked at CPTI by malonyl CoA, a key intermediate in FA synthesis

39
Q

What happens when you have an odd-numbered FA undergo beta oxidation?

A

You end up with the same results, except your last CoA is a propionyl CoA instead of an Acetyl CoA

Propionyl, like propane = 3 carbons

Acetyl = 2 carbons

40
Q

Explain the role of vitamin B12 (cobalamin) in the pathway by which propionyl CoA is converted to succinyl CoA

A

Vitamin B12 functions as a coenzyme to convert L-Methylmalonyl CoA into Succinyl CoA

41
Q

What can happen if someone is B12 deficient?

A

If someone is B12 deficient, they cannot convert L-Methylmalonyl-CoA into Succinyl CoA. This results in a buildup of Methylmalonic acid (MMA) in the blood

Note: The reverse reaction, catalyzed by Methylmalonyl-CoA mutase, is used to determine B12 deficiency

42
Q

What are the possible fates of Succinyl CoA in the cell?

A

Replenish TCA cycle (anaplerotic reaction)

Provide carbons for gluconeogenesis

Oxidation to CO2 + H2O for energy

43
Q

What are the different types of FA oxidation?

A

Alpha

Beta

Omega

44
Q

What kind of oxidation do branched chain FAs undergo?

A

Alpha

45
Q

What is Zellweger syndrome?

A

A defect in peroxisomal biogenesis

46
Q

What are the clinical signs of Zellweger Syndrome?

A

Sign: Elevated C26:0 and C26:1 FAs in plasma

Symptoms include:

Retinitis pigmentosa

Cerebellar ataxia

Chronic polyneuropathy

47
Q

What does Zellweger syndrome cause (pathophysiologically)

A

Causes accumulation of VLCFA in tissues, affecting mainly liver and brain

48
Q

Where does FA oxidation occur for VLCFA and branched chain FAs?

A

Peroxisomes

49
Q

Where does detoxification of hydrophobic xenobiotics occur?

A

Microsomes

50
Q

What kind of oxidation do hydrophobic xenobiotics undergo?

A

Omega

51
Q

The α- and ω- oxidation systems require:

A

The α- and ω- oxidation systems require:

Hydroxylation (Oxygen-insertion)

Reactions using Mixed Function Oxidases (MFOs)

52
Q

What is the cause of Refsum disease?

A

alpha-hydroxylase deficiency

53
Q

What is the treatment of Refsum disease?

A

Dietary restrictions

Reduce intake of Phytanic Acid (from plants)

54
Q

What kind of symptoms do we see with Refsum disease?

A

Mainly neurologic symptoms

55
Q

In the cell, where does omega FA oxidation occur?

A

Smooth Endoplasmic Reticulum

56
Q

What is the importance of omega oxidation?

A

Metabolism of hydrophobic xenobiotics for excretion

Metabolism of normal FA when B-oxidation is defective (removes 1 carbon at a time via multiple oxygen insertion reactions)

57
Q

How does omega FA oxidation clue us into B oxidation issues?

A

Products of omega FA oxidation are C6-C8 dicarboxylic acids for excretion - often an indicator of metabolic disorder in FA oxidation

58
Q

What is the rate determining enzyme of FA synthesis?

What are its regulators?

A

Acetyl-CoA carboxylase (ACC)

Insulin (+), citrate (+), glucagon (-), palmitoyl-CoA (-)

59
Q

What is the regulatory enzyme of Fatty Acid oxidation?

And its regulator(s)?

A

Carnitine acyltransferase I

Malonyl-CoA (-)

60
Q

What is the regulatory enzyme of Ketogenesis?

And its regulator(s)?

A

HMG-CoA synthase

Malonyl-CoA (-)

61
Q

What is the regulatory enzyme of Cholesterol synthesis?

And its regulator(s)?

A

HMG-CoA reductase

Insulin (+), thyroxine (+), glucagon (-), cholesterol (-)

62
Q

What can the brain use outside of glucose for energy?

A

Ketone bodies

Ketone bodies can reduce glucose demand by 75% in starvation

MSK Week 3 (8 decks)

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