Kreb's Cycle Flashcards
Acetyl CoA precursors
Fatty acids, ketone, alcohol
Aconitase
Isomerizes citrate into isocitrate, a step crucial for decarboxylation
Metalloprotein, it specifically requires Fe2+ to function
ª-ketoglutarate and CO2 formation
Enzymes involved
Main products from acetyl-CoA
Dehydrogenases: Rate limiting enzyme of the CAC
Transfer H to NAD+ –> NADH, first NADH produced from acetyl CoA
First carbon lost from acetyl-CoA
Succinyl CoA and CO2 formation
ª-ketoglutarate –> succinyl CoA
ª-ketoglutarate dehydrogenase
2nd NADH produced, H transferred from ª-ketoglutarate
2nd and last C lost from acetyl-CoA
Succinate formation
Enzyme involved
Succinyl-CoA to succinate
*coA is produced
Synthethase produces a covalent bond with energy input (thioester hydrolysis), creating GTP from GDP
GTP then transfers phosphate to ADP, making ATP (the only time in Kreb’s cycle where energy currency is directly produced)
Fumarate formation
Succinate oxidizes to fumarate, reducing FAD to FADH2
Succinyl dehydrogenase transfers the two hydrogen’s from succinate to reduce FAD to FADH2
Oxaloacetate regeneration
Malate to oxaloacetate by malate dehydrogenase
3rd NADH reduced
Oxaloacetate is renewed!
Pyruvate dehydrogenase complex
Enzyme that takes H from pyruvate and adds it to NAD+ to make NADH
Then pyruvate combine with CoA-SH to become acetyl-CoA
One carbon is decarboxylated to CO2
Pyruvate precursors
Glucose, and amino acids
Pyruvate to acetyl CoA regulation
Pyruvate dehydrogenase kinase: High ATP: toward acetyl CoA
Pyruvate dehydrogenase phosphotase: High ADP: backward to pyruvate
Isocitrate to ª-ketoglutarate regulation
Isocitrate dehydrogenase
High ADP and NAD+: forward
High ATP and NADH: backward
ª-ketoglutarate to succinyl CoA regulation
ª-ketoglutarate dehydrogenase
ADP and NAD+, Ca2+: forward
ATP and NADH, succinyl CoA: backward
General Kreb’s cycle regulation
Conversion from ATP/NADH –> ADP/NAD+ means that the cell is metabolically active. So high ADP/NAD+ induces activation at all checkpoints in the Kreb’s cycle
