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BIOCH 200 winter sem 2024 > citric acid cycle > Flashcards

citric acid cycle Flashcards

1
Q

what occurs to Acetyl-CoA in the citric acid cycle?

A

it is oxidized to produce 2CO2 molecules

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2
Q

what are the sources of Acetyl-CoA?

A

carbs, FA and amino acid catabolism

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3
Q

how many C is Acetyl-CoA?

A

2C

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4
Q

what does Acetyl-CoA condense with? what does it form?

A

condenses with oxaloacetate to form citrate

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5
Q

how many carbons are oxidized in the CAC?

A

2 C are oxidized to form 2 CO2 molecules per Acetyl-CoA molecule

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6
Q

how many high energy products are made per Acetyl-CoA?

A

3 NADH
1 FADH 2 / QH2
1 GTP

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7
Q

where does the CAC occur?

A

in the mitochondrial matrix

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8
Q

how many reactions are in the CAC?

A

8

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9
Q

what is the first step in the CAC? what enzyme is used? what is produced?

A

An irreversible reaction with oxaloacetate and Acetyl CoA to produce citrate
-catalyzed by citrate synthase
-generates co-enzyme A

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10
Q

what is the second step in the CAC? what is produced?

A

a reversible isomerization to produce isocitrate

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11
Q

what is the 3rd step in the CAC? what enzyme is used? what is produced?

A

an irreversible oxidative decarboxylation rxn
-catalyzed by isocitrate dehydrogenase (regulated)
-energy capture (produces NADH)

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11
Q

what is the 4th step in the CAC? what enzyme is used? what is produced?

A

an irreversible oxidative decarboxylation to generate Succinyl CoA
-catalyzed by alpha-ketoglutarate dehydrogenase (regulated)
-energy capture step (produces NADH)

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12
Q

what kind of molecule is succinyl CoA?

A

it contains a thioester which makes it a high energy molecule

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13
Q

what is significant of the 4th step in the CAC (synthesis of succinyl CoA)?

A

it is similar to the PDH reaction

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14
Q

what is an example of anabolic processes during the CAC?

A

the conversion of intermediates into amino acids

ex) alpha-ketoglutarate into glutamate

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15
Q

what is the 5th step in the CAC? what is produced?

A

a reversible substrate-level phosphorylation to yield succinate
-energy capture (GTP/ATP)

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16
Q

what occurs when [ADP] decreases in the matrix?

A
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17
Q

what is the 7th step in the CAC? what is produced?

A

a reversible hydration rxn
-conversion of fumerate to malate

18
Q

what is the 8th step in the CAC? what is produced?

A

a reversible oxidation rxn to regenerate oxaloacetate
-energy capture (NADH produced)

19
Q

how is the CAC regulated?

A

regulated by enzymes:
-isocitrate dehydrogenase
-alpha-ketoglutarate dehydrogenase

AND [intermediates]
-NAD+/NADH ratio

20
Q

what are inhibitors of the CAC? What are activators?

A

inhibitors: NADH, ATP, citrate, succinyl CoA
activators: ADP, Ca++

-they reflect energy needs / usage

21
Q

what does high [citrate] affect?

A

it inhibits the CAC
-this is not physiologically relevant

22
Q

what does ATP affect in the CAC?

A

it is a direct allosteric inhibitor for isocitrate dehydrogenase
-conversion of isocitrate into alpha-ketoglutarate

23
Q

what does NADH affect in the CAC?

A

it is a direct allosteric inhibitor for isocitrate dehydrogenase and alpha ketoglutarate complex
-conversion of isocitrate into alpha-ketoglutarate and converion to succinyl CoA

24
Q

what does ADP affect in the CAC?

A

it is a direct activator for isocitrate dehydrogenase
-conversion of isocitrate into alpha-ketoglutarate

25
Q

what does Ca++ affect in the CAC?

A

direct activator for alpha ketoglutarate complex
-converion to succinyl CoA

26
Q

what does succinyl CoA affect in the CAC?

A

inhibits the alpha ketoglutarate complex

27
Q
A
28
Q

what occurs when [ADP] increases in the matrix?

A
29
Q

what can CAC intermediates be used to synthesize?

A

AA, carbs, fats, nucleotides and other compounds

-therefore, [intermediate] must be maintained or the effectiveness of the CAC will decrease

30
Q

what are anaplerotic reactions?

A

rxns that are needed in order to replenish intermediates of the CAC

31
Q

what reactions are anaplerotic?

A

Pyruvate Carboxylase- converts pyruvate to oxaloacetate by adding a carboxyl group

AA breakdown

32
Q

what catalyzes the conversion of pyruvate to oxaloacetate? what kind of reaction is this?

A

catalyzed by pyruvate carboxylase
-anaplerotic rxn

33
Q

what catalyzes the conversion of pyruvate to acetyl-CoA? what kind of reaction is this?

A

pyruvate dehydrogenase complex
-oxidative decarboxilation

34
Q

what molecules activate and inhibit pyruvate carboxylase?

A

activated by acteyl-CoA
inhibited by ADP

35
Q

what affect does acetyl-CoA have on pyruvate dehydrogenase complex?

A

it acts as an inhibitor

36
Q

how many ATP are generated from each Acetyl-CoA?

A

~10 ATP per acetyl-CoA
-20 ATP are made per glucose

37
Q

how many NADH are made per glucose molecule in the CAC?

A

6 NADH
-3 NADH per acetyl-CoA

38
Q

how many FADH2 are made per glucose in the CAC?

A

2 FADH2
-1 per acetyl-CoA

39
Q

how many GTP are made per glucose in the CAC?

A

2 GTP
-1 GTP per acetyl-CoA

40
Q

how many ATP molecules are made from the complete aerobic oxidation of glucose?

A

32 ATP

41
Q

how many ATP are generated from the anaerobic glycolysis of glucose?

A

2 ATP

42
Q

how is lactate used in the CAC?

A

it is used as a metabolic fuel in anaerobic metabolism
-reoxidizes NADH to be used in ETC

43
Q

why do yeast cells consume less glucose in the prescence of oxygen?

A

because aerobic respiration provides a higher energy yield, allowing them to generate more ATP with less glucose.

BIOCH 200 winter sem 2024 (13 decks)

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