easy krebs grind

Which Krebs reaction(s) makes ATP-equivalent?

succinyl-CoA ———(succinyl-CoA synthetase)———> succinate

Hint: CoA is unstable so it has enough energy for GTP/ATP

Lipoamide group is always bound to ____

lysine

Which Krebs reaction(s) makes FADH2?

succinate ——-(succinate dehydrogenase)——→ fumarate

Hint: fumarate begins with F

note is NOT the rxn with fumarase enzyme b/c fumarase is not a dehydrogenase

(HARD) 3 enzymes in the PDC, name and function

(E1) pyruvate dehydrogenase: reduces pyruvate and ALSO decarboxylates it

(E2) dihydrolipoyl transacetylase: turns hydroxyethyl into acetyl and transfers that to CoA-SH

(E3) dihydrolipoyl dehydrogenase: reoxidizes dihydrolipoyllysine

Briefly explain the inner workings of Pyruvate dehydrogenase

E1 takes pyruvate, removes CO2, and binds it to TPP (mysterious molecule), resulting in hydroxyethyl TPP (HETPP)

Hint: although it also decarboxylates, another enzyme is called pyruv decarboxylase so it ca'n’t use that name.

Briefly explain the inner workings of Dihydrolipoyl transacetylase

Lipoyllysine binds to hydroxyethyl TPP (technically oxidizes it) and forms acyl/acetyl lipoyllysine. This acetyl group then goes to CoA-SH to make acetyl-CoA.

Hint: The name means transfer acetyl group. We needed "dihydrolipoyl” to create the acetyl, but really it’s a vehicle that never gets consumed.

Briefly explain the inner workings of Dihydrolipoyl dehydrogenase

E3 reoxidizes lipoyllysine by reducing FAD → FADH2. Since FADH2 is permanently bound to E3, we reoxidize FADH2 by reducing NAD+ → NADH to make better use of those 2 e-

Which Krebs reaction makes CO2?

α-ketoglutarate —-(α-ketoglutarate dehydrogenase)—> succinyl-CoA

isocitrate —-(isocitrate dehydrogenase)—> α-ketoglutarate

Hint: you can tell from sheet when a Carbon is lost.

Which Krebs reaction(s) makes NADH?

isocitrate —-(isocitrate dehydrogenase)—> α-ketoglutarate

α-ketoglutarate —-(α-ketoglutarate dehydrogenase)—> succinyl-CoA

malate —-(malate dehydrogenase)—> oxaloacetate

(BALL) Aconitase is a strange enzyme because…

It dehydrates and rehydrates citrate. In reality it is just a mutase.

(BALL) The Krebs enzyme that is bound tightly to the inner mitochondrial membrane…

succinate dehydrogenase

Makes sense b/c this is the rxn that makes FADH2 and FADH2 is involved in the ETC

Pyruvate oxidation is permanently inhibited by…

Arsenic covalently binding to dihydrolipoyl

Per molecule of acetyl CoA, Krebs cycle makes…

3 NADH, 1 GTP/ATP, 1 FADH2

also 2 CO2, 1 CoA-SH

Which part of metabolism is considered amphibolic?

Krebs cycle is amphibolic because it contains both anabolic and catabolic rxns.

Common inhibitors of Krebs cycle

ATP, NADH, succinyl CoA