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BIOCH 200 > The Citric Acid Cycle > Flashcards

The Citric Acid Cycle Flashcards

1
Q

Where does the CAC Occur?

A

in the mitochondrial matrix

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2
Q

Acetyl-CoA -> Citrate

A

Catalyzed by citrate synthase
Irreversible reaction
Not regulated
-citrate inhibits but only at high concentrations

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3
Q

Citrate -> Isocitrate

A

Isomerization

Reversible

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4
Q

Isocitrate -> alpha-Ketoglutarate

A 
Oxidative decarboxylation
Irreversible reaction
Energy capture (NADH)
Catalyzed by isocitrate dehydrogenase
Regulated
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5
Q

alpha-Ketoglutarate -> Succinyl CoA

A 
Oxidative decarboxylation
Irreversible Reaction
Energy capture (NADH)
Catalyzed by alpha-ketoglutarate dehydrogenase
Similar to PDH reaction
Regulated
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6
Q

Succinyl-CoA

A

High energy intermediate (thioester)

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7
Q

Succinyl-CoA -> Succinate

A

Substrate-level phosphorylation
Reversible reaction
Energy Capture (NTP)

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8
Q

Succinate -> Fumarate

A 
Oxidation
Reversible reaction
Catalyzed by succinate dehydrogenase 
FAD/FADH2 oxidation of C-C single bond 
Integral membrane protein (Complex II)
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9
Q

More about Succinate Dehydrogenase Complex

A

FADH2 is reoxidized by donating electrons to coenzyme Q
QH2 is reoxidized in the electron transport chain
Succinate dehydrogenase is a membrane-bound enzyme and is part of complex II in the ETC

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10
Q

Fumarate -> Malate

A

Hydration

Reversible reaction

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11
Q

Malate -> Oxaloacetate

A

Oxidation
Reversible reaction
Energy capture (NADH)
Regenerates oxaloacetate

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12
Q

Regulation of the Citric Acid Cycle

A

Cyclic, no rate-limiting steps per se

  • affected by NAD+/NADH ratio
  • regulated enzymes
  • affected by concentrations of intermediates
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13
Q

Regulated Enzymes in the CAC

A

Isocitrate dehydrogenase

alpha-ketoglutarate dehydrogenase

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14
Q

Inhibitors and Activators of the CAC

A

Inhibitors: NADH, ATP
Activators: ADP, Ca++

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15
Q

High levels of citrate

A

Inhibits citrate synthase

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16
Q

What does NADH inhibit?

A

Isocitrate dehydrogenase

alpha-ketoglutarate dehydrogenase

17
Q

What does ATP inhibit?

A

Isocitrate dehydrogenase

18
Q

What does ADP activate?

A

Isocitrate dehydrogenase

19
Q

What does Ca++ activate?

A

alpha-ketoglutarate dehydrogenase

20
Q

How to slow down the PDC and the CAC

A

Decreased ADP in the matrix = decreased activity of ATP synthase = increased H+ gradient across IMM = decreased rate of electron transport = decreased oxidation of NADH = decreased NAD+/NADH ratio
ATP synthase is not using a gradient
Decrease in O2 consumption

21
Q

How to speed up the PDC and the CAC

A

Increased ADP in the matrix = increased activity of ATP synthase = decreased H+ gradient across IMM = increased rate of electron transport = increased oxidation of NADH = increased NAD+/NADH ratio
ATP synthase using a gradient
Increase in O2 consumption

22
Q

The CAC is both catabolic and anabolic

A

Amphibolic

CAC intermediates can be used in the synthesis of amino acids, carbs, fats, nucleotides, and other compounds

23
Q

Anaplerotic Reactions

A

Replenish citric acid cycle intermediates
-intermediates may be consumed in other processes
-must be adequate intermediates to continue CAC
Many reactions may be anaplerotic
-amino acid breakdown
-pyruvate carboxylase

24
Q

Pyruvate Carboxylase Catalyzes an Anaplerotic Reaction

A

The formation of oxaloacetate from pyruvate is an important anaplerotic reaction
The reaction is catalyzed by pyruvate carboxylase
This enzyme is activated by acetyl-CoA and inhibited by ADP

25
Q

Functions of the CAC

A

Provide biosynthetic precursors
An important step in the generation of ATP
-CAC generates 10 ATP per acetyl-CoA
-complete aerobic oxidation of glucose yields 32 ATP

26
Q

ATP yield under aerobic conditions

A 
Glycolysis 
-2 net ATP
-2 NADH = 5 ATP
Pyruvate
-2 NADH = 5 ATP
CAC
-6 NADH = 15 ATP
-2 FADH2 = 3 ATP
-2 GTP = 2 ATP

BIOCH 200 (9 decks)

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