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SMP - MNE Exam 1 > Lecture 18: Metabolism of Fat & Ketone Bodies > Flashcards

Lecture 18: Metabolism of Fat & Ketone Bodies Flashcards

1
Q

What is the purpose of β oxidation of FAs?

A

Acetyl-CoA synthesis for ATP generation

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2
Q

What is the most common FA synthesized by our body? How many Cs?

A

Palmitic acid: 16 Cs

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3
Q

How many acetyl-CoAs generate per 1 palmitic acid? How many ATPs?

A

8 acetyl CoAs

108 ATPs

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4
Q

What is the net equation of the beta oxidation of palmitic acid?

A

Palmitic acid + 7 NAD+ + 7 FADH + 7 H2O + 7CoA-SH = 8 acetyl CoA + 7NADH + 7H+ + 7FADH2

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5
Q

Saturated FA β Oxidation Step 1: Enzyme?

A

Acyl-CoA dehydrogenase

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6
Q

Saturated FA β Oxidation Step 1: Substrates/Products?

A

Palmitoyl-CoA + FAD = trans-Δ^2-enoyl-CoA + FADH2

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7
Q

Saturated FA β Oxidation Step 1: Coenzyme?

A

FAD

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8
Q

Saturated FA β Oxidation Step 1: Where is acyl-CoA dehydrogenase located?

A

Mito inner membrane

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9
Q

Which saturated FA β Oxidation enzyme has 3 isozymes? Why?

A

Acyl-CoA dehydrogenase: for different FA chain lengths: very long, medium, and short

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10
Q

Saturated FA β Oxidation Step 1: describe the oxidation of palmitoyl-CoA in detail.

A

Double bond formed between alpha and beta C: point of unsaturation is now formed

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11
Q

Saturated FA β Oxidation: what nomenclature change occurs during this reaction? Which step?

A

Alpha and beta Cs are now called Δ2 and Δ3

Steps 1 and 3

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12
Q

Saturated FA β Oxidation Step 2: Enzyme? What is this enzyme similar to?

A

Enoyl-CoA hydratase, similar to fumarase in TCA

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13
Q

Saturated FA β Oxidation Step 2: Substrates/Products?

A

trans-Δ^2-enoyl-CoA + H2O = L-β-Hydroxy-Acyl-CoA

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14
Q

Saturated FA Beta Oxidation Step 2: Coenzyme?

A

Water

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15
Q

Saturated FA Beta Oxidation Step 1: Rxn type?

A

Oxidation reaction

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16
Q

Saturated FA Beta Oxidation Step 2: Rxn type?

A

Hydration

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17
Q

Saturated FA β Oxidation Step 2: describe the hydration of trans-Δ^2-enoyl-CoA in detail.

A
  • OH added to Δ3 C = βC
  • H added to Δ2 C = αC
    (no more double bond)
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18
Q

Saturated FA Beta Oxidation Step 2: main purpose?

A

Setting the stage for ketone group addition and departure of acety-CoA in step 3

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19
Q

Saturated FA Beta Oxidation Step 3: Enzyme?

A

β-Hydroxyl-Acyl-CoA dehydrogenase

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20
Q

Saturated FA Beta Oxidation Step 3: Substrates/Products?

A

L-β-Hydroxy-Acyl-CoA + NAD+ = β-Ketoacyl-CoA + NADH + H+

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21
Q

Saturated FA Beta Oxidation Step 3: Coenzyme?

A

NAD

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22
Q

Saturated FA Beta Oxidation Step 3: Rxn type?

A

Oxidation

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23
Q

Saturated FA Beta Oxidation Step 3: describe the oxidation of L-β-Hydroxy-Acyl-CoA in detail.

A

β C-OH => β C=O (1 electron taken from the β C and 1 from the O)

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24
Q

Saturated FA Beta Oxidation Step 4: Enzyme? 2 names

A

Acyl-CoA Acetyl Transferase = Thiolase

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25
Q

Saturated FA Beta Oxidation Step 4: Substrates/Products?

A

β-Ketoacyl-CoA +CoA-SH = Acetyl-CoA + myristoyl-CoA

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26
Q

Saturated FA Beta Oxidation Step 4: Coenzyme?

A

None

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27
Q

Saturated FA Beta Oxidation Step 4: Rxn type?

A

Nucleophilic substitution

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28
Q

What is the result of 1 round of FA beta oxidation?

A

FA chain is reduced in length by 2Cs and 1 acetyl-CoA is expelled

29
Q

How does the the β oxidation of unsaturated cis FAs occur?

A
  1. Initial β oxidation steps occur up until the cis double bond
  2. Δ3,Δ2-enoyl-CoA isomerase moves the double bond 1 C closer to C=O so it becomes trans
  3. β oxidation resumes
30
Q

How does the the β oxidation of odd number FAs occur?

A
  1. Usual β oxidation steps

2. Last step: propionyl-CoA (3 Cs) is released with acetyl-CoA

31
Q

What kind of FA is oleic acid (aka olive oil)?

A

Mono-unsaturated FA

32
Q

What happens to the propionyl-CoA released through the β oxidation of odd number FAs?

A
  1. Propionyl-CoA carboxylase converts it to methylmalonyl-CoA (4 Cs) using carbonic acid, biotin, and ATP
  2. Methylmalonyl rearrangement to convert it to succinyl-CoA (using B12)
  3. Succinyl-CoA feeds into the TCA
33
Q

Are all FAs non-anaplerotic and CANNOT contribute to gluconeogenesis (do not form intermediates of a metabolic pathway)?

A

NOPE, odd numbered ones are

34
Q

Where are ketone bodies synthesized?

A

Liver mitochondria exclusively

35
Q

What happens to the ketone bodies produced by the liver once they arrive at target tissues?

A

Converted back to acetyl-CoA to enter TCA

36
Q

What are the 3 types of ketone bodies? Which one is predominant in the blood?

A
  1. Acetoacetate
  2. β-hydroxybutarate (predominant in blood)
  3. Acetone
37
Q

Which 2 ketone bodies are produced from the 3 one?

A

β-hydroxybutarate and acetone are reduced forms of acetoacetate

38
Q

Which ketone body cannot be used as metabolic fuel?

A

Acetone

39
Q

How do ketone bodies affect pH? Why?

A

Very negative so reduce pH

40
Q

Under what conditions does ketogenesis occur?

A

Fasting = TCA cycle intermediates are being used for gluconeogenesis and FA β-oxidation is high = acetyl CoA builds up

41
Q

Describe the 4 steps of ketogenesis to generate all 3 types of ketone bodies.

A
  1. Thiolase: condenses 2 acetyl-CoA together (reverse of last step of FA β-oxidation) = acetoacetyl-CoA
  2. HMG-CoA synthase activated: acetoacetyl-CoA + acetyl-CoA = HMG-CoA
  3. HMG-CoA lyase: HMG-CoA = acetyl-CoA + acetoacetate
    4a. β-hydroxybutarate dehydrogenase: NADH + H+ + acetoacetate = β-hydroxybutarate
    4b. Acetoacetate decarboxylase: acetoacetate = acetone + CO2 (also can happen spontaneously)
42
Q

Does the first acetyl-CoA added during ketogenesis end up in the final product?

A

NOPE

43
Q

Can the brain use FAs for energy? Why/Why not?

A

NOPE because they are bound to albumin in plasma and so do not traverse the blood-brain barrier

44
Q

How to calculate the # of rounds of beta oxidation needed?

A

of acetyl-CoAs produced - 1

45
Q

From what macromolecule does most of the acetyl CoA used in ketogenesis come?

A

FAs

46
Q

Describe the 3 steps of ketone bodies breakdown to generate acetyl-CoA.

A
  1. β-hydroxybutyrate dehydrogenase: ketone body + NAD+ = acetoacetate + NADH
  2. β-ketoacyl-CoA transferase: succinyl-CoA + acetoacetate = acetoacetyl-CoA + succinate
  3. Thiolase: acetoacetyl-CoA = 2 acetyl-CoA
47
Q

What is the only organ that can perform ketogenesis? Why?

A

Liver because it has the enzymes

48
Q

How does the brain switch from using glucose to ketone bodies?

A

Starvation activates β-ketoacyl-CoA transferase

49
Q

What portion of brain energy demands can be met by ketone bodies during starvation?

A

1/3 to 2/3

50
Q

Other than for starvation energy, why else are ketone bodies generated?

A

Detoxification of too many acetyl-CoAs as ketone bodies can be:

  1. Excreted by kidneys
  2. Sweated out
  3. Released in small intestine via bile salts
  4. Exhaled
51
Q

Where are FAs synthesized?

A

Cytoplasm

52
Q

Where does the acetyl-CoA used for FA synthesis come from?

A

Glycolysis and PDC: from mito ONLY

53
Q

Can acetyl-CoA cross the mito inner membrane?

A

NOPE

54
Q

How is acetyl-CoA transferred form the mito to the cytoplasm? Describe the 3 steps.

A

Citrate shuttle:

  1. Citrate synthase: acetyl CoA + oxaloacetate = citrate (TCA step 1)
  2. Citrate transported out of matrix via citrate transporter
  3. Citrate lyase: citrate + ATP = oxaloacetate + acetyl-CoA
55
Q

After transporting acetyl-CoA out of the mito matrix, how does oxaloacetate go back in? 2 ways.

A
  1. Converted to malate and then via malate-alpha-keto-glutarate antiporter
  2. Conversion to malate and then to pyruvate by malic enzyme and then via pyruvate transporter
56
Q

What do malic enzymes use to convert pyruvate to malate and vice versa?

A

NADP/NADPH

57
Q

What is the main enzyme used in FA synthesis?

A

FA synthase

58
Q

What are the 2 main parts of FA synthase?

A
  1. Acyl carrier protein (ACP)

2. 4’-phosphopantetheine chain (same as CoA but it has ACP instead of AMP nucleotide)

59
Q

What is the role of the acyl carrier protein (ACP) in FA synthase?

A

Point of attachment of acyl chain

60
Q

What are the 3 main difference between FA oxidation and synthesis?

A
  1. Oxidation vs reduction
  2. Different enzymes
  3. Acetyl-CoA released vs malonyl-CoA added
61
Q

Describe the steps of FA synthesis.

A
  1. Acetyl-CoA carboxylase: acetyl CoA = malonyl CoA
    1a. Biotin carboxylase: biotin arm + ATP + HCO3- = carboxybiotin
    1b. Transcarboxylase: carboxybiotin + acetyl-CoA = malonyl-CoA
  2. Acetyl-CoA + ACP = Acetyl-ACP (KS subunit) + CoA-SH
  3. Malonyl CoA + ACP = Malonyl-ACP + CoA-SH (phosphopantetheine chain)
  4. Malocyl-ACP + acetyl-ACP = CO2 + β-ketoacyl-ACP
  5. β-ketoacyl-ACP + NADPH = hydroxyacyl-ACP + NADP
  6. hydroxyacyl-ACP = enoyl-ACP + H2O
  7. enoyl-ACP + NADPH = 4C FA chain + NADP
    REPEAT!
62
Q

What FA synthesis step is the one regulated by hormones?

A

Step 1

63
Q

What hormones is step 1 of FA synthesis regulated by?

A

Adrenaline and insulin

64
Q

From what end of the FA do we take off Acetyl-CoAs in beta oxidation?

A

Delta end = where the CoA is

65
Q

What are the 2 ways in which TAGs can enter glycolysis?

A
  1. Odd numbered FAs make succinyl-CoA which can feed into gluconeo
  2. Glycerol can be converted to glycerol-3-phosphate which can be converted to DHAP
66
Q

Why can’t the liver use ketone bodies?

A

It lacks the enzyme β-ketoacyl transferase (step 2 of ketone body breakdown)

67
Q

What kind of people exhale extra acetone?

A

People on a diet (like Atkins) who do not eat carbs so are lacking TCA intermediates and create a lot of acetone to get rid of the excess acetyl-CoA

68
Q

Do people with favism lack enough NADPH to perform biosynthesis?

A

No, because they can create NADPH through the conversion of malate to pyruvate (but not from the PPP)

SMP - MNE Exam 1 (25 decks)

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