Complex reactions

[cwfergus]

Do we have to know like the steps of how pyruvate is formed or the exact steps of the CAC (krebs) ?

like: glucose turns to glucose-6-phosphate, which turns to fructose-6-phosphate which turns to fructose 1,6-diphosphate orrrrr like acetyl coA enters into krebs, turns into citrate, then isocitrate then alpha-ketoglutarate?

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[centersharpie]

No. My kaplan instructor just told me to learn what goes in and what comes out of each rxn. We will only learn the specifics of each step in med school. The best way is to know how many NADHs, or how many turns of the kreb cycle, or how many GTPs (ATPs) come out of the kreb cycle. Stuff like that. Just know what goes in and what comes out.

 

[cwfergus]

Thanks man,
I never took the prep course and im just out of my freshman year! haha im taking it without knowing much of orgo (which im gonna study my ass off with kaplan MCAT premier program 2008-2009) whichi s very detailed.

But okay! so just know that in glycolosis, pyruvate is formed via 2 NADHs and 2 ATPs. from there, in the junction between glycolysis (in cytosol) to the matrix, acetyl CoA is formed due to the decarboxylation of the pyruvate and the oxidation of it, which leads to the addition of a coenzyme A. which will evidentially form acetyl coA whcih will enter the Krebs cycle where 2 CO2 is released, 3 NADHs are produced and 1 FADH2 PER acetyl coA.
But okay sweet, we will hav eto know FMN and cytocrome a3 (last) and all that fun stuff that leads to O2 being reduced to H2O.



PS: i dont know if this is all correct, ive been drinking tonight, this is off of what ive studied this evening a few hours ago,

BASICALLY, what you learnt in Cell biology (BIo102, BIO130) whereever you took it.

 

[cwfergus]

Okay i re-read it!
so like 2ATP + 2NADH's out of glycolysis
2NADHs out of junction
6NADHs out of krebs
2 ATP out of krebs
2 FADH2s out of krebs

8 x 3 = 24 ATP out of NADH's
2 from beginning sooo ( 4ATP)
2 x 2 = 4 ATP out of FADH2
and then we already have 4 ATPs

SOOO around 36 ATP?

that always confuses me though! haha
i get the 8 from junction and citric acid, but the 2 from glycolysis only go through 2!

 

[zogoto]

it's because glycolysis occurs in the cytosol whereas all the CAC steps (including junction) occur in the mitochondria. it takes 1 ATP for the active transport step that moves NADH into the mitochondria (where it needs to be in order to be oxidized to phosphorylate ADP). thus even though those NADH eventually make 3 ATP each, you lose 1 moving it into the mitochondria.

 

[supafield]

TPR teaches 2.5 per NADH and 1.5 per FADH2

and that the NADH from glycolysis only yields 1.5 ATP because it's given straight to ubiquinone via a glycerol phosphate shuttle....

lol when i took it in 2006 they said the NADH from glycolysis only produce 1.5 due to one ATP being expended to transport it to the matrix from the cytoplasm...

Either way just remember 1.5 ATP per Glycolysis NADH....

Total of 30 in euks
32 in proks

it also notes that most texts will cling to 36 and 38 but these are outdated.
So it's probably good to keep that in mind... I highly doubt the MCAT will ask what the theoretical ATP yield of glucose catabolism is in euks and then give you both 30 and 36 as options.

 

[cwfergus]

Wow! My kaplan (like the new version) says 36 ATP and 3/ NADH and 2/ FADH2.

thats weird... thats what i learnt in cell biology too
but ill keep it in mind (2.5 and 1.5) if it asks on the MCAT thanks