atp yield from 1 glucose

[jowen88]

i know this is nitpicky and i understand where the numbers come from and everything, but does AAMC or anyone authoritative have a number they prescribed for this?

is it 30-32 or 36-38?

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[WhiteWashed]

i know this is nitpicky and i understand where the numbers come from and everything, but does AAMC or anyone authoritative have a number they prescribed for this?

is it 30-32 or 36-38?

i've learned 30-32.

 

[TwoPaddles]

i know this is nitpicky and i understand where the numbers come from and everything, but does AAMC or anyone authoritative have a number they prescribed for this?

is it 30-32 or 36-38?

Each book list is as different; I've learned it as 36...but I've seen when they listed it as 32 as well.

 

[Rolling]

From what I've learned you can break it down in the following way.

Glucose will be broken down to yield NRG (energy) in four steps, assuming there is enough O2 present to perform cellular respiration.

In glycolysis (cytoplasm), 2 ATP are necessary, but 4 ATP are made, yielding 2 Net ATP from Glycolysis. In the process 2 NADH are made. The product of glycolysis which will be further broken down is 2 molecules of pyrvuate (both are 3 carbons).

Glycolysis : 2 net ATP (substrate level phosphorylation), and 2 NADH (will be used in the ETC)

In pyruvate decarboxylation, each pyruvate will be converted to acetyl-coa. However, 2 NAD+ will be reduced and will form 2NADH.

Pyruvate Decarboxylation : 2 NADH (will be used in ETC)

Krebs Cycles/TCA cycle

Per one turn of the cycle, acetyl-coa will yield 3NADH,1FADH2, 1ATP (via a GTP intermediate), and one CO2 if you care). However, there are two molecules of acetyl-coa (there were 2 pyruvate). So...

TCA Cycle : 6NADH + 2FADH2 (to be used in the ETC), and 2 ATP (substrate-level phosphorylation)

So at this moment we have the following

2FADH2 (from TCA)
4ATP (substrate-level phosphorylation)
8NADH (pyruvate + TCA)
2NADH (glycolysis)

For the MCAT, you can assume that each NADH will yield 3 ATP, and each FADH2 will yield 2 ATP, though some advanced biochemistry books may argue this is too simplistic.

Keep in mind that the two NADH that are made via glycolysis will actually only produce 2 NET ATP because it costs them an ATP to enter the mitochondria

Oxidative Phosphorylation
2FADH2 x (2 ATP/1FADH2) = 4 ATP total
8 NADH (3ATP/1NADH) = 24ATP total
2 NADH (2ATP/1NADH) = 4 ATP total

That's a total of 32 ATP

Substrate level phosphorylation

2 net ATP from glycolysis + 2 ATP from TCA cycle = 4 ATP

Total of 36 ATP.

Prokaryotes, do not have membrane-bound organelles, so they don't need to sacrifice an ATP for the NADH made from glycolysis. So the total ATP for prokaryotes is 38 ATP.

I hope this helps.

 

[TwoPaddles]

Rolling explained it well. The difference in the net ATP production comes from how many ATP molecules the NADH and FADH2 will yield.

 

[Bernoull]

i know this is nitpicky and i understand where the numbers come from and everything, but does AAMC or anyone authoritative have a number they prescribed for this?

is it 30-32 or 36-38?

I can't remember what my AAMC practice exams said, but u shouldn't see both 32 & 36 are answers to a single Q. Even in med sch Professors from the same biochem dept don't agree on what the ATP yield is per NADH (3 vs 2.5), FADH2 (2 vs 1.5) so there's slight discrepancy. However, MCAT won't trick u on that technicality.

gdluck

 

[CodeBlu]

Yeah, that question is much more likely to appear on any non-AAMC practice test. I think it's more important to understand general trends of electron transport and transfer.

 

[libraryismyhome]

36 when going through some kind of malate stuff
32 or somewhere when it didn't. man,, gotta review this

 

[rmm30]

One thing to keep in mind is that the ATP produced / molecule of glucose is the theoretical yield i.e the max amount of ATP that can be produced. In a cell the actual yield is always lower (averaging around 30). This is because of differences in mitochondrial efficiencies as well as competition bt other biological processes.

nice explanation btw rolling.

 

[junkmail]

I'm studying for the MCAT exam and I had the same question is it 30-32 or 36-38? From my understanding both are used.



Kaplan says:

[each NADH gives 3 ATP, and each FADH2 gives 2 ATP]

Prokaryotes yield 38
Eukaryotes yield 36


(which is what Rolling explained)


HOWEVER, Princeton Review says:

[each NADH gives 2.5 ATP, and each FADH2 gives 1.5 ATP]

Glycolysis (cytoplasm):
used 2 ATP = -2 ATP
yield 4 ATP = 4 ATP
2 NADH = 5 ATP

PDC = 5 ATP

TCA/Krebs
6 NADH = 15 ATP
2 FADH2 = 3 ATP
2 GTP = 2 ATP

PROKARYOTES (no mitochondria) yield 32 ATP

EUKARYOTES (has mitochondria) yield 30 ATP


NADH uses the malate shuttle to yield 2.5 ATP per NADH

Princeton's explanation for eukaryotes:
NADH from glycolysis is transported into the mitochondria using the glycerol phosphate shuttle which bypasses NADH dehydrogenase and arrives directly to ubiquinone, just like FADH2.

So instead of the normal 2.5 ATP formed per NADH
it's 1.5 ATP formed per NADH from glycolysis


Princeton Review notes:

"These numbers are an estimate of the theoretical maximum amount of ATP than can be produced from a single molecule of glucose. As the proton gradient is used to transport other molecules into or out of the matrix, the actual yield may differ depending on the number of protons (i.e., the gradient) available for ATP synthesis."

"These numbers reflect the most recent understanding of ATP synthesis, and as such, may not appear in some textbooks that cling to the previously established counts of 36 ATP per glucose in eukaryotes and 38 ATP per glucose in prokaryotes."




I just don't know which values the MCAT will use 🙁

 

[Rabolisk]

It doesn't matter. Your score on the MCAT won't be affected by this. I guarantee it.