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Biochemistry I > Chapter 17: The Citric Acid Cycle > Flashcards

Chapter 17: The Citric Acid Cycle Flashcards

1
Q

The Citric Acid Cycle is the final common oxidation of

A
  • Acetyl-SCoA to CO2 and H2O
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2
Q

Acetyl-SCoA for the CAC is provided by

A
  • Metabolism of carbohydrates
  • Amino acids (glutamate, alanine)
  • Fatty acids
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3
Q

CAC takes place within

A
  • The semi fluid mitochondrial matrix
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4
Q

CAC generates

A
  • High energy electrons as NADH and FADH2
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5
Q

Electrons lost during the CAC enter

A
  • The electron transport chain

- Undergo oxidative phosphorylation

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6
Q

Electron carriers donate their electrons to oxygen to form

A
  • Water producing ATP
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7
Q

The common intermediate of catabolic reactions

A
  • Acetyl-SCoA
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8
Q

Acetyl-SCoA that enters the CAC comes primarily from

A
  • The PDH reaction
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9
Q

One of the most important sources for Acetyl-CoA

A
  • Pyruvate
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10
Q

Acetyl-SCoA combines with OAA to form

A
  • Citrate
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11
Q

2 molecules of CO2 are released sequentially yielding

A
  • Succinyl CoA
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12
Q

After conversion of Succinyl CoA back to OAA…

A
  • Acetyl-SCoA can be added again and the process continues
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13
Q

1 molecule of OAA can take part in

A
  • The oxidation of many acetyl-SCoAs
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14
Q

One round of the CAC yields

A
  • 3 NADH + 1 FADH2

- 1 high energy GTP + 2 CO2

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15
Q

CAC exhibits no

A
  • Net degradation of intermediates
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16
Q

Cycle intermediates are

A
  • Biosynthetic precursors
  • Nitrogenous bases
  • Porphyrin
  • Amino acids
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17
Q

CAC enzymes

A
  • Citrate synthase
  • Aconitase
  • Isocitrate dehydrogenase
  • alpha-ketoglutarate dehydrogenase
  • Succinyl-SCoA synthetase
  • Succinate dehydrogenase
  • Fumarase
  • Malate dehydrogenase
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18
Q

CAC enzymes are found in

A
  • Balanced proportions

- Concerted gene expression

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19
Q

Citrate synthase is inhibited by

A
  • ATP
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20
Q

Citrate synthase catalyzes

A
  • An irreversible condensation reaction between Acetyl-CoA and oxaloacetate
  • Initiates CAC
  • RATE LIMITING STEP
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21
Q

Citrate is isomerized to

A
  • Isocitrate
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22
Q

Aconitase catalyzes

A
  • An reversible isomerization in readiness for oxidative decarboxylation in subsequent steps
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23
Q

Dehydration is followed by

A
  • Hydration (aconitase step)
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24
Q

Isocitrate dehydrogenase

A
  • Catalyzes the oxidative decarboxylation of isocitrate
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25
Q

Isocitrate dehydrogenase step releases

A
  • Releases the first of two CO2s
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26
Q

Isocitrate dehydrogenase is activated by

A
  • Substrates (isocitrate)
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27
Q

Isocitrate dehydrogenase is inhibited by

A
  • Its products
28
Q

Alpha-ketoglutarate dehydrogenase catalyzes

A
  • The irreversible oxidative decarboxylation of alpha-ketoglutarate
  • Forms succinyl-CoA
29
Q

During the a-ketoglutarate dehydrogenase step, a CO2 is removed from

A
  • A CO2 is removed from the substrate

- NAD- is reduced

30
Q

Alpha-ketoglutarate dehydrogenase multienzyme complex requires

A
  • 5 cofactors (same ones as PDH complex)
31
Q

Alpha-ketoglutarate dehydrogenase complex is inhibited by

A
  • Products and ATP
32
Q

Arsenic poisoning effects

A
  • Alpha-ketoglutarate dehydrogenase
  • PDH
  • It is toxic
33
Q

Succinyl-CoA synthetase works by

A
  • Substrate level phosphorylation
34
Q

Succinyl-CoA synthetase has two

A
  • Isoforms in mammals

- ADP or GDP specific

35
Q

During the Succinyl-CoA step, GDP

A
  • Is converted to GTP, which is then coupled to ADP phosphorylation
  • Produces 1 ATP
36
Q

Succinate dehydrogenase catalyzes

A
  • The oxidation of succinate
  • Reduces FADH
  • Not found in the mitochondrial matrix
37
Q

Reduction of FADH in succinate dehydrogenase releases

A
  • FADH2
38
Q

SDH is an integral protein of

A
  • The inner mitochondrial matrix

- Part of complex II of ETC

39
Q

SDH is competitively inhibited by

A
  • Malonate
40
Q

Fumarase catalyzes

A
  • A reversible hydration reaction

- Trans hydration reaction

41
Q

Fumarase exists in two forms

A
  • Mitochondrial and cytoplasmic isoforms
42
Q

Malate dehydrogenase catalyzes

A
  • Oxidation of malate to OAA
  • NAD+ is reduced to NADH
  • Reaction proceeds readily
43
Q

Malate dehydrogenase step

A
  • Final step

- Regenerates OAA

44
Q

Overall regulation of CAC

A
  • Acetyl-SCoA primarily from PDH: substrate
  • Depends on availability of oxidized cofactors (NAD+ and FAD)
  • Depends on rate of production/utilization of ATP
45
Q

Regulatory steps of CAC

A
  • Citrate synthase
  • Isocitrate dehydrogenase
  • Alpha-ketoglutarate dehydrogenase
46
Q

Citrate synthase regulatory step rate is determined by the availability of

A
  • OAA

- Acetyl-SCoA

47
Q

Citrate synthase regulatory step is inhibited by

A
  • ATP
  • NADH
  • Succinyl- SCoA
  • Citrate
  • Long chain fatty acids
48
Q

Isocitrate dehydrogenase regulatory step is inhibited by

A
  • ATP

- NADH

49
Q

Isocitrate dehydrogenase regulatory step is stimulated by

A
  • NAD+

- ADP

50
Q

Alpha-ketoglutarate dehydrogenase regulatory step is inhibited by

A
  • ATP
  • NADH
  • Succinyl-SCoA
51
Q

Citrate inhibits PFK-1 of

A
  • Glycolysis
52
Q

Substrate level phosphorylation produces

A
  • 1 GTP from succinyl-SCoA synthetase = 1 ATP
53
Q

Oxidative phosphosrylation produces

A
  • 1 NADH from isocitrate dehydrogenase = 2.5 ATP
  • 1 NADH from a-ketoglutarate dehydrogenase = 2.5 ATP
  • 1 FADH2 from succinate dehydrogenase = 1.5 ATP
  • 1 NADH from malate dehydrogenase = 2.5 ATP
54
Q

Total energy production from each round of the CAC

A
  • 10 ATP
55
Q

Energy sources from outside the CAC

A
  • PDH
  • ATP from the CAC + PDH
  • Glycolysis
  • Complete oxidation of glucose to CO2 and H2O
56
Q

Pyruvate dehydrogenase energy production

A
  • 1 NADH = 2.5 ATP
57
Q

ATP from the CAC + PDH energy production

A
  • Total of 12.5 ATP/pyruvate, or 25 ATP/glucose molecule is obtained
58
Q

Glycolysis energy production

A
  • Maximum of 7 ATP by aerobic metabolism
59
Q

Complete oxidation of glucose to CO2 and H20 energy production

A
  • Grand total of 32 ATP
60
Q

Citric Acid Cycle has an anabolic and catabolic role

A
  • Considered to be amphibolic
61
Q

CAC enzymopathies

A
  • Autosomal recessive inheritance
  • Mutation in fumarase gene
  • Mutation in succinate dehydrogenase gene
  • Mutation in a-ketoglutarate dehydrogenase and succinyl-CoA synthetase genes also occur
62
Q

Mutation in the fumarase gene results in

A
  • Severe encephalopathy with seizures
  • Growth/developmental delay
  • Cancer
63
Q

Mutation in succinate dehydrogenase gene results in

A
  • Leigh syndrome

- Associated with vomiting, neuro d/o, rarely get pass 2 y/o

64
Q

The CAC is divided into

A
  • 8 enzyme-catalyzed steps
65
Q

The CAC occurs primarily

A
  • In the mitochondrial matrix of eukaryotic cells
66
Q

The metabolism of acetyl-CoA to carbon dioxide via the Krebs Cycle takes place in the

A
  • Mitochondria
67
Q

Acetyl-CoA enters the Krebs Cycle via condensation with

A
  • Oxaloacetate

Biochemistry I (34 decks)

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