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Biochemistry > Exam 2 Lecture 19 Citric Acid Cycle > Flashcards

Exam 2 Lecture 19 Citric Acid Cycle Flashcards

1
Q

TCA takes place where?

A

Inside the mitochondria

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2
Q

TCA cycle does what to carbon fuels?

A

Oxidizes carbon fuels for harvesting high energy electrons

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3
Q

T/F: TCA cycle is amphibolic

A

True performs catobolism and anabolism

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4
Q

T/F: TCA cycle is not a source of precursors for biosynthesis

A

False. Is a source for biosynthesis

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5
Q

TCA stands for:

A

Tricarboxylic acid cycle

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6
Q

What are the high energy e- carries of the TCA cycle?

A

NADH
FADH2
GTP

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7
Q

Oxidative phosphorylation happens in :

A

Mitochondria

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8
Q

ATP production:

1 NADH = _ ATP
1 FADH2 _ ATP
1 GTP = _ ATP

A

1 NADH = 2.5 ATP
1 FADH2 = 1.5 ATP
1 GTP = 1 ATP

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9
Q

What are types of energy nutrients that will be degraded for the TCA cycle?

A

Fats, polysaccharides, and proteins

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10
Q

Oxidation of 2-carbon units produce:

A
  • 2 CO2 molecules
  • 1 GTP
  • high energy e-s in the form of NADH and FADH2
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11
Q

Acetyl CoA is the activated form of:

A

Acetate

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12
Q

Acetyl CoA is obtained from what 3 energy nutrients?

A
  • Carbohydrates (glucose oxidized into 2 pyruvate, 2 pyruvate decarboxylation into 2 acetyl CoA)
  • Lipids (TAG beta-oxidation into acetyl CoA)
  • Proteins (breakdown into various amino acid and converted to acetyl CoA)
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13
Q

What are the 3 steps of pyruvate to acetyl CoA

A
  1. Decarboxylation (CO2 removed)
  2. Oxidation (2 e- leaving)
  3. Transfer acetyl group to coenzyme A
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14
Q

T/F: In converting pyruvate to acetyl CoA, reactions are coupled to preserve energy to drive formation of NADH and acetyl CoA

A

True

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15
Q

Pyruvate utilizes _ to enter the mitochondria

A

Mitochondrial pyruvate carrier (MPC)

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16
Q

What enzyme catalyzes the decarboxylation of pyruvate?

A

Pyruvate dehydrogenase complex (PDC)

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17
Q

What are the 3 enzymes required for the pyruvate dehydrogenase reaction

A

E1, E2, E3

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18
Q

What are the coenzymes for the pyruvate dehydrogenase reaction

A
  1. TPP
  2. Lipoic acid
  3. FAD
  4. CoA
  5. NAD+
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19
Q

Of the 5 coenzymes for the pyruvate dehydrogenase reaction, which are the catalytic cofactors?

A

TPP
Lipoic acid
FAD

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20
Q

Of the 5 coenzymes for the pyruvate dehydrogenase reaction, which are stoichiometric cofactors?

A

CoA

NAD+

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21
Q

PDC/PDH is regulated via

A

Allosteric interactions and reverse phosphorylation

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22
Q

Hight amounts of acety CoA directly inhibits _

A

PDH/C complex subunit E2 ie increases phosphorylation (kinase) to inactivate PDH/PDC

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23
Q

Accumulation of ADP and pyruvate activates _

A

Phosphatases ie active PDH/PDC

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24
Q

What is the common currency for the TCA cycle?

A

acetyl CoA

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25
Q

PDH links _ to the citric acid cyle (TCA)

A

Glycolysis

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26
Q

What enzyme is used for the 1st step to catalyze condensation of: 4-carbon OAA to citrate?

A

Citrate synthase

27
Q

The hydroxyl group on citrate is not in the proper location for oxidative decarboxylation. What enzyme and its mechanism to form isomerize citrate into isocitrate?

A

Enzyme aconitase via dehydration/hydration moves OH atoms (uses iron-sulfur cluster)

28
Q

What is the rate limiting step in the TCA cycle?

A

Enzyme isocitrate dehydrogenase forms alpha-ketoglutarate

29
Q

Rate limiting step in TCA cycle is the first of what?

A

First of 4 oxidation-reduction reactions

30
Q

What is the unstable intermediate formed by oxidation-reduction of isoctirate

A

Oxalosuccinate (loses CO2 while bound to the enzyme isocitrate dehydrogenase)

31
Q

What enzyme takes alpha-ketoglutarate and forms succinyl CoA

A

Alpha-ketoglutarate dehydrogenase

32
Q

What is the mechanism of alpha-ketoglutarate dehydrogenase

A

Decarboxylate an alpha-ketoacid and creates a thioester linkage with CoA

33
Q

Enzyme used for succinyl CoA into succinate

A

Succinyl CoA synthetase

34
Q

Succinyl CoA synthetase is the only step that directly yields:

A

A high energy phospho-transfer compound (GTP, ATP)

35
Q

Succinyl CoA synthetase yields 2 isozymic forms ie:

A
  1. In tissues that perform many anabolic reactions (liver) yields Succinate + CoA + GTP
  2. In skeletal and heart muscle that perform large amounts of cellular respiration yields Succinate + CoA + ATP
36
Q

Enzyme used for Succinate to Fumarate

A

Succinate dehydrogenase

37
Q

Succinate dehydrogenase catalyzes formation of fumarate while generating

A

FADH2 (high energy substance)

38
Q

Succinate dehydrogenase is located in the _

A

Inner mitochondrial membrane directly associated with ETC Complex II

39
Q

FADH2 is not released from succinate dehydrogenase but instead e-s are passed directly to _ in the ETC

40
Q

What enzyme is used to catalyze Fumarate into malate

A

Fumarase via hydration of fumarate to form L-Malate

41
Q

What enzyme catalyzes the final step of the TCA cycle: Malate into OAA

A

Malate dehydrogenase

42
Q

Oxidation of malate has a positive _

A

Standard free energy

43
Q

NADH inhibits _

A

PDH/C complex subunit E3

44
Q

Phosphatases are also stimulated by _ which increases to initiate muscle contraction

45
Q

Insulin can stimulate FA synthesis via

A

Activating phosphatases and increasing the conversion of pyruvate to acetyl CoA

46
Q

What is the first regulation site in the TCA cycle?

A

Citrate synthase prevents the wasteful hydrolysis of acetyl CoA

47
Q

What is the 2nd regulatory site in the TCA cycle?

A

Isocitrate dehydrogenase allosterically stimulated by ADP enhances enzyme affinity for substrate. NADH also inhibits by directly displacing NAD+

48
Q

What is the 3rd control site in the TCA cycle?

A

Alpha-ketogluturate dehydroenase allosterically inhibited by its products: succinyl CoA and NADH

49
Q

Control at isocitrate dehydrogenase leads to build up of citrate which can transport to the cytosol and signal _

A

Phosphofructokinase and halt glycolysis

50
Q

Control of alpha-ketogluturate dehydrogenase leads to build up of alpha-ketogluturate that can be used for _

A

Synthesis of amino acids and purine bases

51
Q

Why is the TCA cycle anaplerotic?

A

Uses and produces certain substrates; provides intermediates for replenishing TCA cycle

52
Q

What are the 2 major anaplerotic reactions?

A
  1. Degradation of amino acids

2. Carboxylation of pyruvate

53
Q

When energy needs are met, intermediates are used for _ and are replenished by formation of _

A

Used for biosynthesis of other molecules and replenished by formation of OAA from pyruvate

54
Q

OAA biosynthesis into

A

Glucose

aspartate -> other amino acids, purines, and pyrimidines

55
Q

Citrate biosynthesis into

A

Fatty acids and sterols

56
Q

Alpha-ketoglutarate biosynthesis into

A

Glutamate -> other amino acids -> purines

57
Q

Succinyl CoA biosynthesis into

A

Porphyrins, heme, chlorophyll

58
Q

T/F: GTP biosynthesis from substrate level phosphorylation

59
Q

T/F: TCA cycle oxidized 3-carbon units

A

False 2-carbon unites

60
Q

Anaplerotic reactions are required during states of _

A

Low energy

61
Q

T/F: PDH/C is regulated both allosterically and by phosphorylation

62
Q

T/F: TCA cycle is a source of biosynthetic precursors

63
Q

Pyruvate carboxylase is one of the most important anaplerotic enzymes bc

A

Forms OAA from pyruvate (C3->C4); formation of new bond requires ATP and cofactor biotin; activated by acetyl CoA

*distinct from PDC

Biochemistry (32 decks)

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