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USMLE Biochemistry > Pyruvate Dehydrogenase > Flashcards

Pyruvate Dehydrogenase Flashcards

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USMLE® Step 1 flashcards
1
Q

Via what channels does pyruvate enter the inner area of the mitochondria?

A
  • Outer membrane: Voltage-gated porin complex

- Inner: Mitochondrial pyruvate carrier (MPC)

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2
Q

What is the enzyme which turns pyruvate towards gluconeogenesis in the mitochondria?

A

Pyruvate Carboxylase

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3
Q

What is the enzyme which turns pyruvate into Acetyl-Coa?

A

Pyruvate dehydrogenase complex

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4
Q

What molecule can slow down the TCA cycle and increase the levels of acetyl coa?

A

ATP

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5
Q

What enzyme does Acetyl Coa activate?

A

Pyruvate carboxylase

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6
Q

What are the 3 enzymes which make up the pyruvate dehydrogenase complex?

A
  • Pyruvate dehydrogenase (E1)
  • Dihydrolipoyl transacetylase (E2)
  • Dihydrolipoyl dehydrogenase (E3)
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7
Q

What are the 5 co-factors required by the pyruvate dehydrogenase complex?

A
  • NAD+
  • FAD+
  • Coenzyme A (coA)
  • Thiamine
  • Lipoic acid
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8
Q

What is the role of E1 (Pyruvate dehydrogenase)?

A

Converts:

  • Pyruvate
  • Thiamine-PP

into:

  • CO2
  • Thiamine skeleton of pyruvate on to thiamine PP
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9
Q

What is the role of E2 (Dihydrolipoyl transacetylase)?

A

Thimaine pyrophosphate carbon complex combined with lipoic acid to create:

  • Carbon skeleton attached to lipoic acid
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10
Q

What is added to the Carbon skeleton attached to lipoic acid to make acetyl coA?

A

CoA

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11
Q

What is the function of E3 (Dihydrolipoyl dehydrogenase)?

A

Uses NAD and FAD+ cofactors to keep lipoic acid in proper form to be used by E2 subunit

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12
Q

What is the active form of thiamine (B1)?

A

Thiamine pyrophosphate (TPP)

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13
Q

What 4 enzymes is TPP a cofactor for?

A
  • Pyruvate dehydrogenase
  • Alpha-ketoglutarate dehydrogenase (TCA cycle)
  • Alpha-ketoacid dehydrogenase (branched chain amino acids)
  • Transkelotase (HMP shunt)
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14
Q

Thiamine deficiency results in a decreased production of what molecule?

A

ATP

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15
Q

What tissues are most affected by decreased ATP (as a result of thiamine deficiency)?

A

Aerobic tissues (nerves/heart)

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16
Q

What groups get beriberi syndrome?

A

Underdeveloped areas children

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17
Q

What are the symptoms of dry beriberi?

A
  • Polyneuritis

- Muscle weakness

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18
Q

What are the symptoms wet beriberi?

A
  • Tachycardia
  • high-output HF
  • Edema
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19
Q

What are some symptoms of Wernicke-Korsakoff syndrome?

A
  • Confusion

- Confabulation

20
Q

What happens if you give malnourished (e.g alcoholic) patients glucose without thiamine?

A

If thiamine deficient they will get worsened Wernicke-Korsakoff syndrome
- Will be unable to metabolise glucose

21
Q

What is FAD+ synthesised from?

A

B2 - Riboflavin

22
Q

What does adenosine + riboflavin give?

A

FAD+

23
Q

What does FAD+ become when given 2 electrons?

A

FADH2

24
Q

What is NAD+ synthesised from?

A

Niacin (B3)

25
Q

What is niacin synthesised from?

A

Tryptophan

26
Q

What does NAD+ carry electrons as?

A

NADH

27
Q

What is NAD+ useful for?

A

Electron transport

28
Q

What is coenzyme A synthesised from?

A

Pantothenic acid (B5)

29
Q

What does coenzyme A accept and donate?

A

Acyl groups

30
Q

What does lipoic acid bond with to create?

A

Bonds with lysine to create lipoamide

31
Q

What does lipoic acid act as a co-factor for?

A

E2

32
Q

What is lipoic acid inhibited by?

A

Arsenic

33
Q

How does arsenic inhibit lipoic acid to cause disease?

A
  • Binds to lipoic acid

- Inhibits PDH (like thiamine deficiency)

34
Q

What causes arsenic poisoning to create a garlic like breath?

A

Oxidised to arsenois oxide which smells like garlic

35
Q

What are some of the non-specific symptoms of arsenic poisoning

A
  • Vomitting, diarrhea
  • Coma
  • Death
36
Q

How is PDH made inactive?

A

Through phsophorylation by PDH kinase

37
Q

How is PDH made active?

A

Through dephosphorylation by PDH phosphatase

38
Q

What substances activate PDH?

A
  • NAD (incr ratio to NADH)
  • ADP
  • Ca2+
39
Q

What substances inactivate PDH?

A
  • NADH (decreased ratio of NAD to NADH)
  • ACoA
  • ATP
40
Q

How is PDH complex deficiency inherited?

A
  • X-linked usually

- Most commonly due to mutations in PDHA1 gene

41
Q

What part of the pyruvate dehydrogenase complex is affected in PDH complex deficiency?

A

E1-alpha subunit

42
Q

What metabolic issue do babies with PDH complex deficiency present with?

A

Lactic acidosis

43
Q

What are the key findings / symptoms of a baby with PDH complex deficiency?

A
  • Poor feeding, growth failure, developmental delay
  • Elevated alanine
  • Lactic acidosis
44
Q

What are examples of mitochondrial disorders whoch all cause lacic acidosis?

A
  • Pyruvate dehydrogenase complex deficiency
  • Pyruvate carboxylase deficiency
  • Cytochrome oxidase deficiencies
45
Q

How is PDH complex deficiency treated?

A

Supplement:

  • Thiamine
  • Lipoic acid

Ketogenic diet:

  • Low carb (reduces lactic acidosis)
  • High fat
  • Ketogenic amino acis: Lysine and leucine
  • Drives ketone production (instead of glucose)
46
Q

What 2 substances are lysine and leucine converted to?

A

Acetoacetate

Acetyl CoA

  • Straight into TCA cycle
  • Cannot be used for gluconeogensis and back into pyruvate (worsening lactic acidosis)

USMLE Biochemistry (44 decks)

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