Lecture 24: TCA Cycle Flashcards

1
Q

Three steps in formation of Acetyl CoA from pyruvate

A

Decarboxylation
Oxidation
Transfer to CoA
NADH is produced

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2
Q

How does pyruvate enter the mitochondria, and what decarboxylates it once inside

A

Mitochondrial pyruvate carrier

Pyruvate dehydrogenase complex

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3
Q

Pyruvate dehydrogenase requires _ enzymes and _ coenzymes- name them

A
3 enzymes E1, E2, E3
5 coenzymes 
-Thyamine pyrophosphate
Lipoic acid
FAD
NAD
CoA
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4
Q

Pyruvate dehydrogenase is active under which phosphorylation state

A

Dephosphorylated is active

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5
Q

What are positive/negative allosteric regulators of Pyruvate dehydrogenase kinase PDK

A

+ Acetyl Coa, NADH, ATP

- Pyruvate, CoA, NAD+, ADP

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6
Q

What are positive allosteric regulators of Pyruvate dehydrogenase phosphatase PDP

A

Calcium and magnesium

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7
Q

High levels of acetyl CoA will directly inhibit which enzyme of the pyruvate dehydrogenase complex (remember 3 enzymes and 5 coenzymes)

A

E2

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8
Q

Citrate synthase

A

Condensation of 4-carbon oxaloacetate and 2-carbon acetyl CoA to yield Citrate

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9
Q

Aconitase

A

Citrate –> Isocitrate

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10
Q

Isocitrate dehydrogenase

A
Isocitrate-->oxalosuccinate--> a-ketoglutarate
NADH + CO2 formed
Rate limiting step
Activated by ADP
Inhibited by ATP and NADH
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11
Q

a-ketoglutarate dehydrogenase complex

A

a-ketoglutarate–> Succinyl CoA
NADH formed
Inhibited by ATP, succinyl CoA and NADH

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12
Q

Succinyl CoA synthetase

A

Succinyl CoA–> Succinate

*GTP formed- only step yielding high energy molecule

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13
Q

Succinate dehydrogenase

A

Succinate–> Fumarate

FADH2 formed

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14
Q

Where is succinate dehydrogenase located, and where is FADH2 sent when formed by it

A

Located in the inner mitochondrial membrane directly associated with electron transport chain
FADH2 passes electrons directly to Co-Q in the ETC

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15
Q

Fumarase

A

Fumarate–> Malate

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16
Q

Malate dehydrogenase

A

Malate–> Oxaloacetate
NADH formed
Inhibited by excess oxaloacetate or NADH

17
Q

How does insulin help regulate the citric acid cycle

A

Insulin can stimulate fatty acid synthesis by activating phosphatases and increasing conversion of pyruvate to acetyl CoA

18
Q

What is the effect of Arsenite on pyruvate dehydrogenase complex

A

Inhibits function by binding Lipoic acid on E2

19
Q

How does citrate synthase prevent wasteful hydrolysis of Acetyl CoA

A

Oxaloacetate must bind first, and the enzyme undergoes conformational change to accept acetyl CoA

20
Q

What is the second control site in the citric acid cycle

A

Isocitrate dehydrogenase is activated by ADP and inhibited by NADH/ATP

21
Q

What is the third control site in the citric acid cycle

A

a-ketoglutarate dehydrogenase
Allosterically inhibited by its products- Succinyl CoA and NADH
Also inhibited by ATP

22
Q

What happens when excess citrate builds up because of the control point at isocitrate dehydrogenase, what happens to the citrate

A

It is transported to the cytosol and signals phosphofructokinase to halt glycolysis

23
Q

What happens to a-ketoglutarate when it builds up

A

It can be used for synthesis of amino acids and purine bases

24
Q

What are the two major anaplerotic reactions that replenish TCA cycle intermediates- and when are they important

A

Degradation of amino acids
Carboxylation of pyruvate
Most important during states of low energy