Glycolysis

[bajoneswadup]

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Does glycolysis occur in RBCs? I'm looking at TBR bio book 2, chapter 3, #51. Like reallyyy!!!??? Please tell me the real MCAT isn't like this question or I'm about to cry.

Lactic acid is the end product of glycolysis in:

A) RBCs
B) brain tissue cells
C) adipose tissue cells
D) heart and muscle tissue cells

Answer is...A..

 

[chiddler]

Yes you should know that RBC's only use glycolysis as their energy source and therefore produce lactic acid.

don't feel too bad, this is just one of many facts that you have to memorize.

 

[rjosh33]

Does glycolysis occur in RBCs? I'm looking at TBR bio book 2, chapter 3, #51. Like reallyyy!!!??? Please tell me the real MCAT isn't like this question or I'm about to cry.

Lactic acid is the end product of glycolysis in:

A) RBCs
B) brain tissue cells
C) adipose tissue cells
D) heart and muscle tissue cells

Answer is...A..

The concept this question is testing isn't that RBC's undergo glycolysis, per se. It's more testing whether you realize that RBC's are glorified bags of hemoglobin, with no DNA and no mitochondria (or other organelles). Therefore, RBCs can only do glycolysis exclusively -- meaning they need to do fermentation to regenerate the NAD+ -- whereas the others can do oxidative phosphorylation as long as sufficient oxygen is present.

This would actually be a good MCAT topic, but it would probably be tested with a less convoluted question.

 

[chiddler]

The concept this question is testing isn't that RBC's undergo glycolysis, per se. It's more testing whether you realize that RBC's are glorified bags of hemoglobin, with no DNA and no mitochondria (or other organelles). Therefore, RBCs can only do glycolysis exclusively -- meaning they need to do fermentation to regenerate the NAD+ -- whereas the others can do oxidative phosphorylation as long as sufficient oxygen is present.

This would actually be a good MCAT topic, but it would probably be tested with a less convoluted question.

i disagree. it's exactly that RBC's undergo glycolysis. and this question does not seem convoluted...it's just asking if you know that RBC's don't use oxidative phosphorylation for their energy.

 

[rjosh33]

i disagree. it's exactly that RBC's undergo glycolysis. and this question does not seem convoluted...it's just asking if you know that RBC's don't use oxidative phosphorylation for their energy.

Um, and the entire reason they don't undergo oxidative phosphorylation is because they don't have mitochondria, like I said. Numerous questions on practice tests refer back to this concept of being anucelate and devoid of organelles, though usually asking about (lack of) DNA of RBCs.

As for whether it's convoluted or not, sure, you're probably right. Of course, when you know exactly what a question is asking, it doesn't seem confusing. If you're unfamiliar with the details of RBC makeup, then it's a different story.

 

[Temperature101]

But what if the process was anaerobic

 

[chiddler]

Um, and the entire reason they don't undergo oxidative phosphorylation is because they don't have mitochondria, like I said. Numerous questions on practice tests refer back to this concept of being anucelate and devoid of organelles, though usually asking about (lack of) DNA of RBCs.

As for whether it's convoluted or not, sure, you're probably right. Of course, when you know exactly what a question is asking, it doesn't seem confusing. If you're unfamiliar with the details of RBC makeup, then it's a different story.

i'm not disagreeing with your facts. i just think you embellished the approach to the answer way too much.

 

[chiddler]

But what if the process was anaerobic?

what do you mean?

 

[MedPR]

Um, and the entire reason they don't undergo oxidative phosphorylation is because they don't have mitochondria, like I said. Numerous questions on practice tests refer back to this concept of being anucelate and devoid of organelles, though usually asking about (lack of) DNA of RBCs.

As for whether it's convoluted or not, sure, you're probably right. Of course, when you know exactly what a question is asking, it doesn't seem confusing. If you're unfamiliar with the details of RBC makeup, then it's a different story.

Actually, you're incorrect. Prokaryotes don't have mitochondria and they still undergo oxphos. In other words, no mitochondria does not mean no oxphos, as you are suggesting.

RBCs don't undergo oxphos because their entire goal is to maximize gas exchange. If they commit O2 to some other internal process, they will not be able to dump as much O2 into tissues. RBCs undergo glycolysis because they need energy, but it would be dumb for them to consume O2 when the primary goal is to pass out O2. It's like a girl scout eating a box of cookies everytime she sells a box.

The question doesn't require you to know all of that, though. All you have to know is that RBCs undergo glycolysis as their sole source of energy.

 

[rjosh33]

Actually, you're incorrect. Prokaryotes don't have mitochondria and they still undergo oxphos. In other words, no mitochondria does not mean no oxphos, as you are suggesting.

Actually, no, I'm not incorrect. The fact that prokaryotes use their plasma membranes as analogues to the mitochondrial membrane is irrelevant to my point and my answer. There are no answer choices that include prokaryotes, and I repeatedly specifically referred to RBCs -- any other inferences drawn were done in error.

RBCs don't undergo oxphos because their entire goal is to maximize gas exchange. If they commit O2 to some other internal process, they will not be able to dump as much O2 into tissues. RBCs undergo glycolysis because they need energy, but it would be dumb for them to consume O2 when the primary goal is to pass out O2.

Yeah, I know. And how do they accomplish minimal O2 consumption? By being devoid of oxygen-consuming organelles, like that of the mitochondria.

The question doesn't require you to know all of that, though. All you have to know is that RBCs undergo glycolysis as their sole source of energy.

To answer this question, that's fine. But the multiple differences between RBCs and other cells in the body seems to be high-yield material. I was just trying to convey as much to the OP; not sure why that seems to be such a problem.

 

[SpecterGT260]

Rjosh is correct here and the hair splitting over prokaryotes is... just really really beside the point.

All of the listed tissues use glycolysis. In an anaerobic environment you must generate lactate to regenerate NAD to allow further glycolysis to proceed.

This happens in RBCs because they are devoid of mitochondria. The lactate leaches into the plasma and is reconverted to useful intermediates by the liver (I think).

The other tissues have mitochondria and are eukaryotic (it hurt to have to say that....) so they can use pyruvate to enter the krebs cycle. Unless overwhelmed, these tissues will not generate lactate.... and that is assuming they have the proper enzymes.... I dont remember the expression there

 

[MedPR]

Rjosh is correct here and the hair splitting over prokaryotes is... just really really beside the point.

All of the listed tissues use glycolysis. In an anaerobic environment you must generate lactate to regenerate NAD to allow further glycolysis to proceed.

This happens in RBCs because they are devoid of mitochondria. The lactate leaches into the plasma and is reconverted to useful intermediates by the liver (I think).

The other tissues have mitochondria and are eukaryotic (it hurt to have to say that....) so they can use pyruvate to enter the krebs cycle. Unless overwhelmed, these tissues will not generate lactate.... and that is assuming they have the proper enzymes.... I dont remember the expression there

Not really.

True or false.

In eukaryotes mitochondria are necessary for oxphos. Since prokaryotes do not have mitochondria, they do not undergo oxphos. False.

It's not splitting hairs. MCAT requires that you know minute details like this.

Saying that RBCs don't do oxphos because they don't have mitochondria is backwards, and would be an incorrect answer on the MCAT. RBCs don't do oxphos because it would be conterproductive to their goal of maximum gas exchange. In other words, they don't have mitochondria because they don't want to do oxphos, not the other way around.

A partially right answer is a completely wrong answer on the MCAT. Paying attention to details (splitting hairs, as you say) is the difference between a 14 and a 15.

 

[SpecterGT260]

Not really.

True or false.

In eukaryotes mitochondria are necessary for oxphos. Since prokaryotes do not have mitochondria, they do not undergo oxphos. False.

It's not splitting hairs. MCAT requires that you know minute details like this.

Look up "strawman argument". Nobody said that prokaryotes dont undergo ox phos. It was said that that is irrelevant to the question. The MCAT doesn't require you to consider irrelevant information. Trust me 😉

 

[chiddler]

Look up "strawman argument". Nobody said that prokaryotes dont undergo ox phos. It was said that that is irrelevant to the question. The MCAT doesn't require you to consider irrelevant information. Trust me 😉

you're missing the point.

and please stop being so damn condescending.

 

[SpecterGT260]

you're missing the point.

and please stop being so damn condescending.

No. I am not missing any point. The statement that RBCs do not undergo ox phos bc they lack mitochondria is factually correct. The fact that another life form is able to do it sans mitochondria has no bearing on the validity of that statement because RBCs are subject to other restraints stemming from the species which gives rise to them. Introducing the prokaryote information convolutes the issue and is asinine at best. I am no more condescending than those who are trying to bust chops by introducing irrelevant technicalities.

I can see because I have eyes. False? Several cave species have eyes that are vestigial.... but who gives a crap. If we expand application of every fact to encompass the entire universe we can always find exceptions. So we define a system and that system in the question stem was clearly human organs.

 

[Temperature101]

what do you mean?

Doesn't glysolysis happen under anaerobic condition as well...In that case oxidative phosphorilation does not occur and the cell straight to fermentation after glycolysis...

 

[SpecterGT260]

Not really.

True or false.

In eukaryotes mitochondria are necessary for oxphos. Since prokaryotes do not have mitochondria, they do not undergo oxphos. False.

It's not splitting hairs. MCAT requires that you know minute details like this.

Saying that RBCs don't do oxphos because they don't have mitochondria is backwards, and would be an incorrect answer on the MCAT. RBCs don't do oxphos because it would be conterproductive to their goal of maximum gas exchange. In other words, they don't have mitochondria because they don't want to do oxphos, not the other way around.

A partially right answer is a completely wrong answer on the MCAT. Paying attention to details (splitting hairs, as you say) is the difference between a 14 and a 15.

Requoting your edit. U are not wrong in your reasoning. Just in your assumption that the ideas are mutually exclusive. And IMO you are a little backwards here. Or... inside out if we are being true to the facts that we are reorganizing.

Why do RBCs not do ox phos? Because they lack the machinery.
Why do they lack the machinery? Because it would suck if your blood consumed all of your oxygen in transport.

The concepts stated earlier in no way preclude understanding of the biological need for anaerobic metabolism in RBCs. And doing it this way avoids attributing willed acts to insentient subunits of a larger being.... basically- different people are allowed to organize information in different ways to arrive at the same answer. You are not in control of the specific concepts being tested when there is conceptual overlap and strict adherence to your logic could leave you in a position to miss a question on organelle composition. I've taken somewhere in the neighborhood of 30 medical school tests. Trust me, this is an endless source of frustration.

 

[SpecterGT260]

Doesn't glysolysis happen under anaerobic condition as well...In that case oxidative phosphorilation does not occur and the cell straight to fermentation after glycolysis...

Technically speaking glycolysis is always an anaerobic process. The aerobic part is the electron cascade fed by the krebs cycle.

 

[SpecterGT260]

Oh... also remember that one of the krebs cycle enzymes is the SAME as the 2nd transport chain enzyme. Little factoid that gets overlooked due to the segmented organization of most biochem courses... mind blown when I first realized it