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Kaplan: Biochemistry Part I > Chapter 13: Citric Acid Cycle and Oxidative Phosphorylation > Flashcards

Chapter 13: Citric Acid Cycle and Oxidative Phosphorylation Flashcards

1
Q

What are other names for the citric acid cycle?

A

“TCA” cycle
tricarboxylic acid cycle
Krebs cycle

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2
Q

What is the energy released from oxidation in the citric acid cycle saved as?

A

NADH, FADH2, and guanosine triphosphate (GTP)

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3
Q

Is there hormonal control of the citric acid cycle?

A

no

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4
Q

What is the only enzyme in the citric acid cycle that is not found in the matrix of the mitochondria?

A

succinate dehydrogenase

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5
Q

What enzyme catalyzes the rxn: GTP +ADP ⟷ GDP+ATP?

A

diphosphate kinase

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6
Q

What inhibitis isocitrate dehydrogenase?

A

NADH and ATP

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6
Q

What is the major control enzyme of the TCA cycle?

A

isocitrate dehydrogenasse

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7
Q

What is isocitrate dehydrogenase activated by?

A

ADP

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8
Q

What enzyme acts as PDH in the citric acid cycle, in that it needs the same coenzymes and cofactors to effectively function?

A

α-ketoglutarate dehydrogenase

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9
Q

What are the cofactors/coenzymes required for the proper utilization of α-ketoglutarate dehydrogenase?

A

thiamine
lipoic acid,
CoA,
FAD,
NAD

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10
Q

Another name for Succinyl-CoA synthetase?

A

succinate thiokinase

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11
Q

What is the substrate level phosphorylation step that succinyl CoA synthetase catalyzes?

A

GDP to GTP

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12
Q

Where is succinate dehydrogenase found? What is another function for it?

A

On the inner mitochcondrial membrane where it also functions as complex II of the electron transport chain

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13
Q

What is the function of citrate synthase in the citric acid cycle?

A

condenses the incoming acetyl group with oxaloacetate to form citrate

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14
Q

Draw out all the reactions and steps in the citric acid cycle.

A

Refer to image for answer

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15
Q

What is another function for citrate besides an intermediate in the citric acid cycle?

A

citrate may leave the mitochondria (citrate shuttle) to deliver acetyl-CoA into the cytoplasm for fatty acid synthesis

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16
Q

What is another function of succinyl-CoA besides an intermediate of the citric acid cycle?

A

Succcinyl-CoA is a high-energy intermediate that can be used for heme synthesis and to activate ketone bodies in extrahepatic tissues

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17
Q

What is another use for malate besides as an intermediate in the citric acid cycle?

A

malate can leave the mitochondria (malate shuttle) for gluconeogenesis

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18
Q

When intermediates are drawn out of the citric acid cycle does it slow or speed up?

A

it slows

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19
Q

What are the 2 reactions of the citric acid cycle?

A

NADH + O2 -> NAD + H2O ΔG = -56 kcal/mol
FADH2 + O2 -> FAD + H2O ΔG= -42 kcal/mol

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20
Q

What shuttles transfer electrons into the mitochondria for delivery to the ETC if NADH is produced in the cytoplasm?

A

the malate or α-glycerol phosphate shuttle

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21
Q

Once NADH has been oxidized, can the NAD be used again?

A

NAD can be used again by enzymes that require it

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22
Q

Where is FADH2 produced? What enzymes produce it?

A

by succinate dehydrogenase in the citric acid cycle and by Fatty Acyl CoA dehydrogenase the α-glycerol phosphate shuttle also takes FADH2 to the ETC

Both enzymes located in the inner membrane and can reoxidize FADH2

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23
Q

What is the function of O2 in the electron transport chain?

A

to accept electrons

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24
Q

Draw out the steps in oxidative phosphorylation.

A

refer to the diagram

25
Q

Which enzyme oxidized NADH in the electron transport chain?

A

NADH dehydrogenase (complex I)

It oxidizes NADH to NAD and then delivers its electrons into. the chain

26
Q

What is the order by which the electrons are carried in the ETC to major inner membrane components?

A
  1. NADH dehydrogenase (complex I) accepts electrons from NADH
  2. Coenzyme Q (a lipid)
  3. Cytochrome b/c1 (an Fe/heme protein); complex III
  4. Cytochrome c (an Fe/heme protein)
  5. Cytochrome a/a3 (a Cu/ heme protein; cytochrome oxidase, complex IV transfers electrons to O2
27
Q

Succinate dehydrogenase and the α -glycerol phosphate shuttle enzyme re-oxidize their FADH2 and pass electrons directly to what main protein/lipid carrier located in the in the electron transport chain?

A

directly to Coenzyme Q

28
Q

What are the 3 major complexes of the ETC?

A

Complexes I, III, and IV (NADH dehydrogenase, cytochrome b/c1 and cytochrome a/a3)

29
Q

The electricity generated by the ETC is used to run pumps (translocators), which drive protons from which part of the mitochondria to which part?

A

from the matrix space across the inner membrane the into the intermembrane space creating a small proton (or pH) gradient

30
Q

ATP synthesis by oxidative phosphorylation uses the energy of the proton gradient and is carried out by what complex that spans the inner membrane of the mitochondria?

A

F0/F1 ATP synthase complex

31
Q

As protons flow into the mitochondria through the F0 component their energy is used by the F1 component (ATP synthase) to do what?

A

phophorylate ADP using Pi

32
Q

Lactic acidosis in a MI is responsible for what specific changes in the heart?

A

protein precipitation and coagulation necrosis

33
Q

What are some major biochemical effects when there is effective inhibition of the ETC?

A
  • decreased O2 consumption
  • increased intracellular NADH/ NAD and FADH2/FAD ratios
  • decreased ATP
34
Q

What are important inhibitors of the ETC to remember?

A

cyanide and CO (carbon monoxide)

antimycin (cytochrome b/c1), doxorubicin (CoQ), and oligomycin (F0/F1 ATP synthase)

35
Q

Cyanide MOA?

A

deadly poison because it binds irreversibly to cytochrome a/a3 preventing electron transfer to O2, and producing many of the same changes seen in tissue hypoxia

36
Q

What are major sources of cyanide?

A
  • burning polyurethane (foam stuffing in furniture and mattresses)
  • Byproduct of nitroprusside (released slowly; thiosulfate can be used to destroy the cyanide)
37
Q

What are some antidotes for cyanide poisoning? MOA?

A

nitrites it given rapidly; they convert hemoglobin to methemoglobin which binds cyanide in the blood before reaching the tissue.

sodium thiosulfate

O2 also given if possible

38
Q

What is the MOA by which CO can interfere with effective ETC action?

A

binds to cytochrome a/a3 but less tightly than cyanide. It also binds to hemoglobin displacing O2

39
Q

Symptoms of CO poisoning?

A

headache, nausea, tachycardia, and tachypnea

Lips and cheeks turn cherry red

Respiratory depression

coma

40
Q

How to treat CO poisoning?

41
Q

What are some sources of CO poisoning?

A
  • propane heaters and gas grills
  • vehicle exhaust
  • tobacco smoke
  • house fires
  • methylate chloride-based paint strippers
42
Q

What are uncouplers of the ETC? definition

A

chemicals that decrease the proton gradient

43
Q

What are some biochemical effects of uncouplers of the ETC?

A
  • decreased ATP synthesis
  • increased O2 consumption
  • increased oxidation of NADH
44
Q

Because rate of the ETC increases, with no ATP synthesis what is energy released as?

45
Q

What are some important uncouplers of the ETC?

A

2,4 dinitrophenol (2,4-DNP) and aspirin (and other salicylates)

46
Q

What is the natural uncoupling protein found in brown adipose tissue?

A

(UCP (uncoupling protein), formerly called thermogenin)

47
Q

Function of thermogenin?

A

allows energy loss as heat to maintain a basal temperature around the kidneys, neck breastplate, and scapulae in newborns

48
Q

What are the most sensitive and specific markers of AMI (acute myocardial infarction)?

A

Troponin I and troponin T

49
Q

Aspirin in high doses used to treat RA can result in uncoupling of oxidative phosphorylation. This leads to what biochemical symptoms in the body?

A
  • increased O2 consumption
  • depletion of hepatic glycogen
  • pyretic effect of toxic doses of salicylate
  • symptoms may vary depending on degree of salicylate intoxication from tinnitus to pronounced CNS and acid-base disturbance
50
Q

What are the products of molecular O2 species that are partially reduced?

A

ROS reactive oxygen species

51
Q

What is the result of ROS formation in the body?

A

they react rapidly with lipids to cause peroxidation with proteins, and with other substrates, resulting in denaturation and precipitation in tissues

52
Q

What are some ROS species?

A
  • superoxide (O2-)
  • Hydrogen peroxide (H2O2)
  • hydroxyl radical (OH)
53
Q

The small quantities of ROS produced in the ETC production are destroyed by what enzymes?

A

catalase and superoxide dismutase

54
Q

What are conditions in which the rate of ROS can increase dramatically?

A

in conditions such as reperfusion injury in a tissue that has been temporarily deprived of O2

55
Q

Describe ATP and NADH levels in tissue that has been temporarily deprived of O2?

A

ATP levels will be low and NADH levels high

56
Q

How is reperfusion injury to tissue caused?

A

There is deprivation initially to the tissue so when O2 is suddenly introduced, there is a burst of activity in the ETC, generating incompletely reduced ROS

57
Q

In the case of erythrocytes how are large amounts of superoxide generated?

A

by spontaneous dissociation of O2 from hemoglobin; products are methemoglobin and superoxide

58
Q

Low levels of what in glucose 6 phosphate dehydrogenase deficiency result in accumulation of the destructive hydrogen peroxide?

59
Q

Does excess NADH inhibit or stimulate the citric acid cycle?

A

inhibits citric acid cycle

Kaplan: Biochemistry Part I (27 decks)

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