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AAMC Question Kreb Cycle
#1 Posted : Monday, June 29, 2020 8:37:21 PM
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In the AAMC Official Prep Section Bank of the Biological Sciences there is a stand-alone that has really confused me.

It asks "How many molecules of reduced electron carrier are generated during conversion of ╬▒-ketoglutarate to oxaloacetate in the citric acid cycle?" The answer to this question is 3 - 2 NADH and 1 FADH

I understand we produce 2 NADH here (1 for each acetyl-coA) but I was under the impression that each Kreb cycle produces 1 FADH2 when Succinate goes to Fumurate (1 for each acetyl - coA molecule equalling 2 in total).

I am now very confused - I thought FADH were only produced in this step in the Kreb's cycle because in total 2 turns of the Kreb cycle only produces 2 FADH (both during Succinate to Fumarate)?

#2 Posted : Tuesday, June 30, 2020 4:15:14 PM
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Hi Justine,

I would recommend that you get familiar with the Citric acid cycle, including what the intermediates are, where along the cycle the NADHs, CO2s, GTP and FADHs are being produced, and the enzymes involved.

Per Acetyl-CoA that enters the cycle you get 3 NADHs, 1 FADH2 and 1 GTP.

From Alpha-ketoglutarate to Succinyl-CoA: you get 1 NADH, 1 CO2
From Succinyl-CoA to Succinate: you get 1 GTP
From Succinate to Fumarate: you get 1 FADH2
From Fumarate to Malate:(nothing that you need to remember here)
From Malate to Oxaloacetate: you get 1 NADH

Therefore in total you get 3 electron carriers (2 NADHs, 1 FADH2).

A great way to remember them is by NAC NAC GA FA NA.

Hope to helps! :)

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