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(J) Biochemistry Test 3 > Lecture 24 - Citric Acid Cycle > Flashcards

Lecture 24 - Citric Acid Cycle Flashcards

1
Q

What are the high energy substances produced from the TCA cycle?

L24 S5

A
  • NADH
  • FADH2
  • GTP
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2
Q

What common molecule do fats, carbohydrates, and proteins enter the TCA?

L24 S5

A

Acetyl CoA

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3
Q

How is pyruvate converted to acetyl CoA?

L24 S8

A
  • decarboxylation
  • oxidation
  • transfer to CoA
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4
Q

How does pyruvate enter into the mitochondria?

L24 S9

A

MPC (mitochondrial pyruvate carrier)

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5
Q

What is the pyruvate dehydrogenase complex and what are its cofactors?

L24 S10

A

Trimer:

  • E1
  • E2
  • E3

Catalytic cofactors:

  • thiamine pyrophosphate (TPP)
  • lipoic acid
  • FAD

Stoichiomoetric cofactors:

  • CoA
  • NAD+
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6
Q

How is PDH regulated?

L24 S11-12

A
  • high acetyl CoA inhibits E2
  • phosphorylation of E2 inhibits function
  • high ADP or pyruvate activates via dephosporylation
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7
Q

What is the function of citrate synthase?

L24 S14-15

A

Takes acetyl CoA (2), oxaloacetate (4), and water to make citrate (6).

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8
Q

What does aconitase do?

What special feature does this reaction have?

What is gained from this reaction?

L24 S16-17

A

Converts citrate (6) to isocitrate (6).

Forms intermediate of cis-aconitate.

Puts hydroxyl group on carbon that will allow for decarboxylation.

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9
Q

What does isocitrate dehydrogenase do?

What special feature does this reaction have?

L24 S18-19

A

Dehydrogenates isocitrate (6) to form intermediate of oxalosuccinate which is then is decarboxylated to form α-ketoglutarate (5).

Dehydrogenation converts NAD+ to NADH and H+.

CO2 is produced from decarboxylation.

***rate limiting step***

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10
Q

What does α-ketoglutarate dehydrogenase complex do?

What special feature does this reaction have?

L24 S20-21

A

Converts α-ketoglutarate (5) to succinyl CoA (4).

Forms high energy thioester bond.

Decarboxylation produces CO2.

Hydrogen from thiol of CoA converts NAD+ to NADH.

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11
Q

What does succinyl CoA synthase do?

What special feature does this reaction have?

L24 S22-23

A

Converts succinyl CoA (4) to succinate (4).

Produces GTP (in liver) or ATP (in skeletal and heart muscle) through phosphate level phosphorylation using high energy thioester bond with CoA.

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12
Q

What does succinate dehydrogenase do?

What special features does this reaction have?

L24 S24-25

A

Converts succinate (4) to fumarate (4) via dehydrogenation.

Dehydrogenation converts FAD to FADH2.

Enzyme is located in inner mitochondrial membrane.

FADH2 is not released from the enzyme as the electrons are passed to Co-Q (complex 2) in the electron transport chain.

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13
Q

What does fumarase do?

L24 S26-27

A

Converts fumarate (4) to L-malate (4) via hydration of double bond.

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14
Q

What does malate dehydrogenase do?

L24 S28-29

A

Dehydrogenates malate (4) to form oxaloacetate (4) and H+.

Dehydrogenation converts NAD+ to NADH.

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15
Q

What enzymes of the citric acid cycle have regulatory mechanisms?

L24 S30; 35-36

A
  • pyruvate dehydrogenase
  • isocitrate dehydrogenase
  • α-ketogultarate dehydrogenase
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16
Q

What factors regulate pyruvate dehydrogenase activity?

L24 S30

A

Activators:

  • pyruvate
  • ADP

Inhibitors:

  • NADH
  • ATP
  • acetyl CoA
17
Q

What factors regulate isocitrate dehydrogenase?

L24 S35

A

Activators:

-ADP

Inhibitors:

  • ATP
  • NADH
18
Q

What factors regulate α-ketogluturate dehydrogenase?

L24 S36

A

Inhibitory:

  • ATP
  • succinyl CoA
  • NADH
19
Q

What is an anaplerotic reaction and what are the examples of anaplerotic reactions in the TCA cycle?

Under what conditions do they occur?

L24 S38

A

Fed conditions:

-carboxylation of pyruvate to form acetyl CoA

Starved conditions:

  • degradation of amino acids
  • glutamate (Gln/Pro/His/Arg) enters as α-ketoglutarate
  • propionyl CoA (intermediate for Thr/Met/Ile/Val) enters as succinyl CoA
  • Phe/Tyr/Asp enter as fumarate
20
Q

What citric acid cycle intermediates are used in anabolic functions and what are they used to generate?

L24 S39

A

Citrate:

  • fatty acids
  • sterols

α-ketoglutarate:

  • glutamate
  • certain AAs
  • purines

Succinyl CoA:

  • porphyrins
  • heme
  • chlorophyll

Oxaloacetate:

  • aspartate
  • certain AAs
  • purines
  • pyrimidines

(J) Biochemistry Test 3 (10 decks)

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