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Biochem Exam 3 > 24 - Citric Acid Cycle > Flashcards

24 - Citric Acid Cycle Flashcards

1
Q

The citric acid cycle’s main purpose is to oxidize _______ fuels for harvesting high energy _______.

A

Carbon

Electrons

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2
Q

The citric acid cycle is _________, meaning it undergoes catabolism and anabolism.

A

Amphibolic

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3
Q

The citric acid cycle is the source of precursors for biosynthesis and takes place inside the ________.

A

Mitochondria

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4
Q

What are other names for the citric acid cycle?

A

Tricarboxylic acid cycle (TCA)

Krebs cycle

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5
Q

The citric acid cycle is the oxidation of 2-carbon units to produce what?

A

2 CO2 molecules
1 GTP
High energy electrons in the form of NADH and FADH2

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6
Q

This is the activated form of acetate.

A

Acetyl CoA

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7
Q

Acetyl CoA can be obtained from three energy nutrients, which are…

A

Carbohydrates
Lipids
Proteins

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8
Q

To get acetyl CoA from pyruvate (glycolysis) there are 3 steps that must occur, which are…

A

Decarboxylation
Oxidation
Transfer acetyl group to coenzyme A (CoA)

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9
Q

The reactions to get acetyl CoA from pyruvate are coupled to preserve _______ to drive the formation of NADH and acetyl CoA.

A

Energy

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10
Q

Pyruvate must first enter the mitochondria, and to do this it utilizes…

A

Mitochondrial Pyruvate Carrier (MPC)

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11
Q

This enzyme catalyzes the decarboxylation of pyruvate.

A

Pyruvate dehydrogenase complex (PDH or PDC)

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12
Q

The pyruvate dehydrogenase reaction requires what?

A

3 enzymes

5 coenzymes

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13
Q

What are the 3 enzymes required for the PDH reaction?

A

E1
E2
E3

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14
Q

What are the 5 coenzymes required for the PDH reaction?

A

Catalytic cofactors – Thiamine pyrophosphate (TPP); Lipoic acid; FAD

Stoichiometric cofactors – CoA; NAD+

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15
Q

What are the reactants for the PDH reaction?

A

Pyruvate; NAD+; CoA

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16
Q

What are the products for the PDH reaction?

A

Acetyl CoA; Co2; NADH; H+

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17
Q

The PDH complex is considered (ACTIVE/INACTIVE) when it is phosphorylated, and (ACTIVE/INACTIVE) when it is dephosphorylated.

A

Inactive

Active

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18
Q

PDH is regulated by _________ interactions and reverse _________.

A

Allosteric

Phosphorylation

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19
Q

In the PDH complex, high ________ directly inhibits E2.

A

Acetyl CoA

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20
Q

In the PDH complex, products increase __________ of PDH E2, while accumulation of ADP and pyruvate activate _________.

A

Phosphorylation

Phosphatases (dephosphorylation)

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21
Q

In the PDH complex, all energy containing nutrients should be converted to…

A

Acetyl CoA

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22
Q

The citric acid cycle occurs under (ANAEROBIC/AEROBIC) conditions and produces more energy from glucose than glycolysis.

A

Aerobic

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23
Q

This is what links glycolysis to the citric acid cycle.

A

Pyruvate dehydrogenase (PDH)

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24
Q

The first step in the citric acid cycle is the condensation of 4-carbon _________ and 2-carbon acetyl group of _________.

A

Oxaloacetate

Acetyl CoA

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25
Q

Oxaloacetate reacts with acetyl CoA + _______ and yields ________ and CoA.

A

Water

Citrate

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26
Q

What is the first step (oxaloacetate to citrate) catalyzed by?

A

Citrate synthase

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27
Q

In the second step, citrate isomerize to _________. The hydroxyl group of citrate is not in the proper location for oxidative decarboxylation.

A

Isocitrate

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28
Q

In the isomerization of citrate to isocitrate, dehydration/hydration moves OH atoms via the enzyme….

A

Aconitase

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29
Q

Aconitase uses an _______-_______ cluster to bind citrate.

A

Iron-sulfur

30
Q

This is the first of 4 oxidation-reduction reactions. It is the rate limiting step of the citric acid cycle.

A

Isocitrate dehydrogenase

31
Q

Isocitrate is converted to __________ using ________ ________.

A

alpha-Ketoglutarate

Isocitrate dehydrogenase

32
Q

In the conversion of isocitrate to alpha-Ketoglutarate, there is an unstable intermediate, __________, that loses CO2 while bound to the enzyme.

A

Oxalosuccinate

33
Q

This complex is similar to the pyruvate dehydrogenase complex (PDH/PDC). It catalyzes a similar reaction.

A

alpha-Ketoglutarate dehydrogenase

34
Q

Both PDH and alpha-Ketoglutarate dehydrogenase complex reactions decarboxylate an alpha-ketoacid and create a _________ linkage with CoA.

A

Thioester

35
Q

The alpha-ketoglutarate dehydrogenase converts _________ to _________.

A

alpha-Ketoglutarate

Succinyl CoA

36
Q

Succinyl CoA contains what?

A

High energy thioester bond

37
Q

This is the only step that directly yields a high energy phospho-transfer compound (GTP, ATP).

A

Succinyl CoA synthetase

38
Q

The succinyl CoA synthetase converts _________ to ________.

A

Succinyl CoA

Succinate

39
Q

In tissues that perform many anabolic reactions (liver), succinyl CoA synthetase converts succinyl CoA + ________ + _______ into succinate + _________ + _________.

A

Phosphate (Pi); GDP

CoA; GTP

40
Q

In places that perform a large amount of cellular respiration (skeletal and heart muscle), succinyl CoA synthetase converts succinyl CoA + ________ + _______ into succinate + ________ + ________.

A

Phosphate (Pi); ADP

CoA; ATP

41
Q

Succinate dehydrogenase catalyzes the formation of ________ into ________ while generating ________.

A

Succinate
Fumarate
FADH2

42
Q

Where is succinate dehydrogenase located?

A

Inner mitochondrial membrane

43
Q

Succinate dehydrogenase is located in the inner mitochondrial membrane and is directly associated with the ________ _______ ________ (Complex II).

A

Electron transport chain

44
Q

FADH2 is actually not released from the enzyme (succinate dehydrogenase), but electrons are passed directly to ______ in the electron transport chain.

A

Co-Q

45
Q

Fumarase catalyzes the hydration of _________ to _________.

A

Fumarate

L-Malate

46
Q

This is the final step of the citric acid cycle in which what enzyme is used?

A

Malate dehydrogenase

47
Q

The oxidation of malate has a (POSITIVE/NEGATIVE) standard free energy.

A

Positive

48
Q

Malate dehydrogenase recognizes specifically ________, and the reactions are driven by the use of the products which are ________ and ________.

A

L-Malate
Oxaloacetate
NADH

49
Q

In the final step of the citric acid cycle, oxaloacetate and NADH go on to be used for what?

A

Oxaloacetate — Citrate synthase (repeat cycle)

NADH — electron transport chain

50
Q

High ________ directly inhibits PDH complex subunit E2.

A

Acetyl CoA

51
Q

Energy ________ of the cell dictates PDH complex activity.

A

Charge

52
Q

Phosphatases are also stimulated by _______ which increases to initiate muscle contraction.

A

Calcium (Ca2+)

53
Q

________ can stimulate fatty acid synthesis by activating phosphatases and increasing the conversion of pyruvate to acetyl CoA (precursor for fatty acids).

A

Insulin

54
Q

Citrate synthesis prevents the wasteful hydrolysis of ________.

A

Acetyl CoA

55
Q

T/F. Oxaloacetate binds to the enzyme first, then enzyme undergoes the configurational changes to accept citrate. The condensation reaction yields acetyl CoA.

A

False. Oxaloacetate binds to the enzyme first, then enzyme undergoes the configurational changes to accept acetyl CoA. The condensation reaction yields citrate.

56
Q

The control site is isocitrate dehydrogenase. It is allosterically stimulated by _______, enhancing enzyme affinity for substrate. Reaction product, _______ also inhibits by directly displacing _______.

A

ADP
NADH
NAD+

57
Q

This control site is alpha-ketoglutarate dehydrogenase. This complex is similar to PDH and is allosterically inhibited by its products, ________ and ________.

A

Succinyl CoA

NADH

58
Q

Control at isocitrate dehydrogenase leads to a build up of citrate (easily converted from isocitrate) which can transport to the cytosol and signal ___________ and halt _________.

A

Phosphofructokinase

Glycolysis

59
Q

Alpha-ketoglutarate that builds up from enzyme inhibition can be used for synthesis of _______ ______ and _______ _______.

A

Amino acids

Purine bases

60
Q

The TCA cycle is __________, meaning it has “fill up” reactions that provide intermediates to replenish the cycle. Two major reactions are the degradation of amino acids and the carboxylation of pyruvate.

A

Anaplerotic

61
Q

In this anaplerotic reaction, ________ carboxylation replenishes oxaloacetate.

A

Pyruvate

62
Q

In this anaplerotic reaction, which amino acids are degraded to replenish alpha-ketoglutarate?

A 
Gln
Pro
His
Arg
**Lead to Glutamate
63
Q

In this anaplerotic reaction, which amino acids are degraded to replenish succinyl CoA?

A 
Thr
Met
Ile
Val
**Lead to Propionyl CoA
64
Q

In this anaplerotic reaction, which amino acids are degraded to replenish fumarate?

A

Phe
Tyr
Asp

65
Q

In this anaplerotic reaction, which amino acids are degraded to replenish oxaloacetate?

A

Asn – leads to Asp

66
Q

When energy needs are met, intermediates are drawn for biosynthesis of other molecules. They are replenished by formation of oxaloacetate from ________.

A

Pyruvate

67
Q

The citric acid cycle oxidizes _____ carbon units.

A

2

68
Q

PDH (or PDC) is regulated both _________ and by _________.

A

Allosterically

Phosphorylation

69
Q

The citric acid cycle is a source of _________ precursors.

A

Biosynthetic

70
Q

Anaplerotic reactions are required during states of low ________.

A

Energy

Biochem Exam 3 (10 decks)

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