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Biochemistry > Citric Acid Cycle > Flashcards

Citric Acid Cycle Flashcards

1
Q

What is the TCA cycle?

A

Oxidizes carbon fuels for harvesting high energy electrons, amphibolic, and occurs inside mitochondria

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2
Q

Broad overview of TCA?

A

Step 1: degradation of energy nutrients
Step 2: Acetyl CoA pool
Step 3: Acetyl CoA entry into TCA

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3
Q

1 NADH= ___ ATP

A

2.5

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4
Q

1 FADH= ____ ATP

A

1.5

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5
Q

1 GTP=____ATP

A

1

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6
Q

Where can Acetyl CoA be obtained from?

A

Carbs, Lipids, and Proteins

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7
Q

What 3 steps occur to get Acetyl CoA from pyruvate?

A

Decarboxylation
Oxidation
Transfer acetyl group to CoA also get NADH in the process

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8
Q

How does pyruvate enter the mitochondria and what happens to it?

A

Through mitochondrial pyruvate carrier and from there PDC catalyzes the decarboxylation of pyruvate

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9
Q

What is requried for pyruvate dehydrogenase reaction?

A

Three Enzymes: E1,E2, E3

5 Coenzymes: TPP, Lipoic acid, FAD, CoA, NAD+

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10
Q

What regulates Pyruvate dehydrogenase?

A

Allosteric interactions and reverse phosphorylation

High Acetlyl CoA also directly inhibits E2 and ADP and pyruvate activate phosphatases to activate PDC

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11
Q

How does the citric acid cycle occur?

A

Under aerobic conditions in the mitochondria and makes more energy from glucose than glycolysis

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12
Q

What is the first step of Krebbs?

A

Oxaloacetate reacts with acetyl CoA and water to give citrate and CoA. It is catalyzed by citrate synthase

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13
Q

What occurs after Citrate is formed?

A

(2) Citrate is converted to isocitrate by Aconitase which uses an iron sulfur cluster to bind citrate

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14
Q

What occurs after Isocitrate is formed?

A

(3) Isocitrate is converted to a-ketogluterate by Isocitrate dehydrogenase This is the RLS*** also prodduces NADH

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15
Q

What is the RLS of Krebbs?

A

Isocitrate to a-ketogluterate by Isocitrate dehydrogenase

It is the first of four redox reactions to occur (produces NADH)

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16
Q

What occurs after a-ketogluterate is formed?

A

(4)a-ketoglutarate is converted to succinyl CoA by the a-ketoglutarate dehydrogenase complex and generates NADH

17
Q

What is significant about succinyl CoA?

A

It has a high energy thioester bond when it is hydrolyzed it directly yields a high energy phospho transfer compound such as GTP or ATP

18
Q

What occurs after Succinyl CoA is formed?

A

(5) Succinly CoA is converted to Succinate via Succinyl CoA synthetase and yields GTP(in liver) (ATP in heart and skeletal mm)

19
Q

What occurs after Succinate is formed?

A

(6) Succinate is converted to Fumarate via succinate dehydrogenase it yields FADH2

20
Q

What occurs after Fumarate is formed?

A

(7) Fumarate is converted to L-Malate via Fumarase

21
Q

What is significant about succinate dehydrogenase?

A

It is located in the inner mitochondrial membrane and directly associated with ETC complex II.

22
Q

What occurs after Malate is formed?

A

(8) Malate is converted to OAA via Malate Dehydrogenase which produces NADH

23
Q

What is the significance of malate dehydrogenase?

A

It is the final step and oxidation of malate has positive standard free energy and reactions are driven by use of products OAA-citrate synthase and NADH-ETC

24
Q

What inhibits PDH complex E3?

A

NADH (high energy charge inhibits, and low energy charge stimulates)

25
Q

In TCA what can stimulate phosphatases to activate PDH?

A

Calcium, insulin(stimulates fatty acid synthesis for pyruvate to Acetyl CoA),

26
Q

Calcium, Mg, ADP, NAD, CoA, Pyruvate, and Insuline ____ PDC activity.

A

Activate

27
Q

Acetyl CoA,NADH, ATP, Arsenite ____ PDC activity.

A

Inhibit

28
Q

What prevents wasteful hydrolysis of acetly CoA?

A

Citrate Synthase, 1st control site

29
Q

What is the second control site in TCA?

A

Isocitrate dehydrogenase, it is allosterically stimulated by ADP enhancing the enzyme affinity for substrate and produces NADH which inhibits by displacing NAD+

30
Q

Thrid control site in TCA?

A

A-ketoglutarate dehydrogenase, Allosterically inhibited by its products succinyl CoA and NADH

31
Q

How can the three checkpoints regualte other metabolic pathways?

A

Control at Isocit. dehydro. can lead to build up of citrate which inhibits PFK and stops glycolysis
a-ketoglut. that build up from enzyme inhibition can be used for synthesis of amino acids and purine bases

32
Q

How many carbon units are oxidized in TCA?

A

2

Biochemistry (14 decks)

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