Lecture 2 - TCA Cycle Flashcards
What is the main purpose of TCA cycle?
Produce energy!
Where does TCA cycle occur?
- Mitochondria in eukaryotes
- Cytosol in prokaryotes
Why does TCA cycle only work in one direction?
3 reactions have high negative delta G’s, making their pathways essentially irreversible
Which 3 reactions of TCA cycle have high negative delta G’s?
1) Citrate synthase
2) Isocitrate dehydrogenase
3) Alpha-ketoglutarate dehydrogenase
What 2 molecules are needed to make citrate?
Acetyl-CoA and oxaloacetate
Which enzyme catalyzes the conversion of oxaloacetate to citrate and what type of reaction is this?
- Citrate synthase
- Condensation reaction
What is the cofactor in the conversion of oxaloacetate to citrate?
H2O -> CoA-SH
What inhibits citrate synthase?
Succinyl-CoA, ATP, and NADH
What is the intermediate in the conversion of citrate to isocitrate?
Cis-aconitate
Does aconitase work in one or both directions?
Both
What are the cofactors in the conversion of citrate to isocitrate?
- H2O out
- H2O in
What is the rate limiting step of TCA cycle?
Step 3, isocitrate dehydrogenase
What is lost in the conversion of isocitrate to alpha-ketoglutarate?
CO2
What type of reaction occurs for isocitrate to be converted to alpha-ketoglutarate?
Oxidative decarboxylation since NADH is formed (or NADPH if in cytosol)
Isocitrate dehydrogenase is an ______ enzyme
Allosteric
What activates isocitrate dehydrogenase?
ADP (low energy)
What inhibits isocitrate dehydrogenase?
ATP and NADH (high energy)
Which enzymes catalyzes the conversion of isocitrate to alpha-ketoglutarate?
Isocitrate dehydrogenase
What are the cofactors in the conversion of isocitrate to alpha-ketoglutarate?
NAD+ -> NADH + H+ (will be NADP+ and NADPH if in cytosol)
Alpha-ketoglutarate dehydrogenase has the same mechanism as _____
Pyruvate dehydrogenase
What are the cofactors in the conversion of alpha-ketoglutarate to succinyl-CoA?
- TPP, FAD, and lipoic acid
- CoA-SH in
- NAD+ -> NADH
Which enzymes catalyzes the conversion of alpha-ketoglutarate to succinyl-CoA?
Alpha-ketoglutarate dehydrogenase complex
What inhibits alpha-ketoglutarate dehydrogenase?
NADH and succinyl-CoA
Is the conversion of isocitrate to alpha-ketoglutarate reversible and why?
No because CO2 is released
Is the conversion of alpha-ketoglutarate to succinyl-CoA reversible and why?
No because CO2 is released
Which enzyme catalyzes the conversion of succinyl-CoA to succinate?
Succinyl-CoA synthetase
What are the cofactors in the conversion of succinyl-CoA to succinate?
- GDP + Pi -> GTP
- CoA-SH out
What type of reaction occurs for succinyl-CoA to be converted to succinate?
Substrate level phosphorylation
Succinate is ____
Symmetrical
Which enzyme catalyzes the conversion of succinate to fumarate?
Succinate dehydrogenase
What are the cofactors in the conversion of succinate to fumarate?
FAD -> FADH2
What is the delta G value of the conversion of succinate to fumarate?
0
What is special about succinate dehydrogenase?
It is involved in the ETC
Which enzyme catalyzes the conversion of fumarate to L-malate?
Fumarase
What is the cofactor in the conversion of fumarate to L-malate?
H2O in
Which enzyme catalyzes the conversion of L-malate to oxaloacetate?
Malate dehydrogenase
What are the cofactors in the conversion of L-malate to oxaloacetate?
NAD+ -> NADH + H+
What activates citrate synthase?
ADP
What activates alpha-ketoglutarate dehydrogenase?
Ca2+
