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
2
Q
Acetyl-SCoA for the CAC is provided by
A
- Metabolism of carbohydrates
- Amino acids (glutamate, alanine)
- Fatty acids
3
Q
CAC takes place within
A
- The semi fluid mitochondrial matrix
4
Q
CAC generates
A
- High energy electrons as NADH and FADH2
5
Q
Electrons lost during the CAC enter
A
- The electron transport chain
- Undergo oxidative phosphorylation
6
Q
Electron carriers donate their electrons to oxygen to form
A
- Water producing ATP
7
Q
The common intermediate of catabolic reactions
A
- Acetyl-SCoA
8
Q
Acetyl-SCoA that enters the CAC comes primarily from
A
- The PDH reaction
9
Q
One of the most important sources for Acetyl-CoA
A
- Pyruvate
10
Q
Acetyl-SCoA combines with OAA to form
A
- Citrate
11
Q
2 molecules of CO2 are released sequentially yielding
A
- Succinyl CoA
12
Q
After conversion of Succinyl CoA back to OAA…
A
- Acetyl-SCoA can be added again and the process continues
13
Q
1 molecule of OAA can take part in
A
- The oxidation of many acetyl-SCoAs
14
Q
One round of the CAC yields
A
- 3 NADH + 1 FADH2
- 1 high energy GTP + 2 CO2
15
Q
CAC exhibits no
A
- Net degradation of intermediates
16
Q
Cycle intermediates are
A
- Biosynthetic precursors
- Nitrogenous bases
- Porphyrin
- Amino acids
17
Q
CAC enzymes
A
- Citrate synthase
- Aconitase
- Isocitrate dehydrogenase
- alpha-ketoglutarate dehydrogenase
- Succinyl-SCoA synthetase
- Succinate dehydrogenase
- Fumarase
- Malate dehydrogenase
18
Q
CAC enzymes are found in
A
- Balanced proportions
- Concerted gene expression
19
Q
Citrate synthase is inhibited by
A
- ATP
20
Q
Citrate synthase catalyzes
A
- An irreversible condensation reaction between Acetyl-CoA and oxaloacetate
- Initiates CAC
- RATE LIMITING STEP
21
Q
Citrate is isomerized to
A
- Isocitrate
22
Q
Aconitase catalyzes
A
- An reversible isomerization in readiness for oxidative decarboxylation in subsequent steps
23
Q
Dehydration is followed by
A
- Hydration (aconitase step)
24
Q
Isocitrate dehydrogenase
A
- Catalyzes the oxidative decarboxylation of isocitrate
25
Isocitrate dehydrogenase step releases
- Releases the first of two CO2s
26
Isocitrate dehydrogenase is activated by
- Substrates (isocitrate)
27
Isocitrate dehydrogenase is inhibited by
- Its products
28
Alpha-ketoglutarate dehydrogenase catalyzes
- The irreversible oxidative decarboxylation of alpha-ketoglutarate
- Forms succinyl-CoA
29
During the a-ketoglutarate dehydrogenase step, a CO2 is removed from
- A CO2 is removed from the substrate
| - NAD- is reduced
30
Alpha-ketoglutarate dehydrogenase multienzyme complex requires
- 5 cofactors (same ones as PDH complex)
31
Alpha-ketoglutarate dehydrogenase complex is inhibited by
- Products and ATP
32
Arsenic poisoning effects
- Alpha-ketoglutarate dehydrogenase
- PDH
- It is toxic
33
Succinyl-CoA synthetase works by
- Substrate level phosphorylation
34
Succinyl-CoA synthetase has two
- Isoforms in mammals
| - ADP or GDP specific
35
During the Succinyl-CoA step, GDP
- Is converted to GTP, which is then coupled to ADP phosphorylation
- Produces 1 ATP
36
Succinate dehydrogenase catalyzes
- The oxidation of succinate
- Reduces FADH
- Not found in the mitochondrial matrix
37
Reduction of FADH in succinate dehydrogenase releases
- FADH2
38
SDH is an integral protein of
- The inner mitochondrial matrix
| - Part of complex II of ETC
39
SDH is competitively inhibited by
- Malonate
40
Fumarase catalyzes
- A reversible hydration reaction
| - Trans hydration reaction
41
Fumarase exists in two forms
- Mitochondrial and cytoplasmic isoforms
42
Malate dehydrogenase catalyzes
- Oxidation of malate to OAA
- NAD+ is reduced to NADH
- Reaction proceeds readily
43
Malate dehydrogenase step
- Final step
| - Regenerates OAA
44
Overall regulation of CAC
- Acetyl-SCoA primarily from PDH: substrate
- Depends on availability of oxidized cofactors (NAD+ and FAD)
- Depends on rate of production/utilization of ATP
45
Regulatory steps of CAC
- Citrate synthase
- Isocitrate dehydrogenase
- Alpha-ketoglutarate dehydrogenase
46
Citrate synthase regulatory step rate is determined by the availability of
- OAA
| - Acetyl-SCoA
47
Citrate synthase regulatory step is inhibited by
- ATP
- NADH
- Succinyl- SCoA
- Citrate
- Long chain fatty acids
48
Isocitrate dehydrogenase regulatory step is inhibited by
- ATP
| - NADH
49
Isocitrate dehydrogenase regulatory step is stimulated by
- NAD+
| - ADP
50
Alpha-ketoglutarate dehydrogenase regulatory step is inhibited by
- ATP
- NADH
- Succinyl-SCoA
51
Citrate inhibits PFK-1 of
- Glycolysis
52
Substrate level phosphorylation produces
- 1 GTP from succinyl-SCoA synthetase = 1 ATP
53
Oxidative phosphosrylation produces
- 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
Total energy production from each round of the CAC
- 10 ATP
55
Energy sources from outside the CAC
- PDH
- ATP from the CAC + PDH
- Glycolysis
- Complete oxidation of glucose to CO2 and H2O
56
Pyruvate dehydrogenase energy production
- 1 NADH = 2.5 ATP
57
ATP from the CAC + PDH energy production
- Total of 12.5 ATP/pyruvate, or 25 ATP/glucose molecule is obtained
58
Glycolysis energy production
- Maximum of 7 ATP by aerobic metabolism
59
Complete oxidation of glucose to CO2 and H20 energy production
- Grand total of 32 ATP
60
Citric Acid Cycle has an anabolic and catabolic role
- Considered to be amphibolic
61
CAC enzymopathies
- 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
Mutation in the fumarase gene results in
- Severe encephalopathy with seizures
- Growth/developmental delay
- Cancer
63
Mutation in succinate dehydrogenase gene results in
- Leigh syndrome
| - Associated with vomiting, neuro d/o, rarely get pass 2 y/o
64
The CAC is divided into
- 8 enzyme-catalyzed steps
65
The CAC occurs primarily
- In the mitochondrial matrix of eukaryotic cells
66
The metabolism of acetyl-CoA to carbon dioxide via the Krebs Cycle takes place in the
- Mitochondria
67
Acetyl-CoA enters the Krebs Cycle via condensation with
- Oxaloacetate
