Lecture 306: TCA cycle Flashcards
1
Q
homolactic fermentation
A
- anaerobic [muscles]
- pyruvate reduced to lactate
- no net change in oxidation state
- tissues with high [O2] can burn lactate for fuel
2
Q
how liver can use lactate
A
- glycogenesis precursor
3
Q
pyruvate oxidation requires ____ and does _____
A
- requires acetyl-CoA
- pyruvate converted to acetyl-CoA via PDH complex
4
Q
respiratory chain regenerates ____
A
- NAD+
5
Q
oxidative phosphorylation synthesizes ___
A
- ATP
6
Q
PDH complex
A
- irreversible
- requires TPP, LA, FAD, NAD+ and CoA
- via E1, E2 and E3
7
Q
regulation of PDH complex
A
- acetyl-CoA and NADH [major products] = feedback inhibitors
- PDH phosphatase = activated by insulin
- PDH kinase
8
Q
regulation of PDH kinase in TCA cycle
A
- activate the inhibitor [indirectly inhibit] = ATP, NADH and acetyl-CoA
- inhibit the inhibitor [indirectly activate] = ADP and pyruvate
9
Q
TCA cycle takes place in ____
A
mitochondria
10
Q
TCA step 1
A
- citrate synthase
- only IRREVERSIBLE step
- main regulatory step
11
Q
TCA step 2
A
- successive dehydration and hydration rxns
- reversible
12
Q
TCA step 3
A
- decarboxylation
- reversible but favors forward
- requires NAD+
13
Q
TCA step 4
A
- reversible but favors forward
- decarboxylation
- requires TPP, LA, CoA, NAD+ and FAD
- mechanism similar to PDH complex
14
Q
TCA step 5
A
- formation of succinate, GTP and CoA
- reversible
- requires GDP OR ADP and phosphate
- succinyl-CoA = high energy molecule = drives synthesis of GTP/ ATP
15
Q
nucleoside diphosphate kinase
A
- converts GTP formed to ATP
- brain/ heart = ATP-linked enzyme
- liver = GTP-linked enzyme
16
Q
TCA step 6
A
- complex 2
- reversible
- requires FAD [covalently bound to enzyme]
- bound to mitochondrial membrane = necessary for re-oxidation of FAD
17
Q
TCA step 7
A
- fumerate to malate via fumerase
- reversible
18
Q
TCA step 8
A
- reforms oxaloacetate [and NADH]
- reversible but rxn moves forward because of very low concentration of oxaloacetate
19
Q
regulation of citrate synthase
A
- most important step of TCA cycle
- NADH, succinyl-CoA and citrate = inhibitors
20
Q
regulation of isocitrate dehydrogenase
A
- rate determining step
- NADH and ATP = inhibitors
- ADP = activate
21
Q
regulation of alpha-keto. dehydrogenase
A
- NADH and succinyl-CoA = inhibitors
