E. Coli vs paramecium ATP production

[km1865]

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I was doing a Kaplan BS section tests and came across a question asking about ATP production in e coli living in the intestine vs a paramecium..

So, the correct answer was that paramecium produce 18 times as much ATP (36 vs 2 for e coli) since they are eukaryotes...

HOWEVER The explanation says "E. Coli are prokaryotes that lack mitochondria and can only use glycolysis for energy production."

Is this correct, E. Coli (specifically) cannot undergo aerobic respiration (because other bacteria can, in which case the net theoretical ATP yield would be 38ATP/ glucose) or does it have to do with no oxygen availability in the intestine...

I chose the answer saying that they both produce relatively equal amounts of ATP.

Can anyone clarify, thanks

 

[docntrainin]

I was doing a Kaplan BS section tests and came across a question asking about ATP production in e coli living in the intestine vs a paramecium..

So, the correct answer was that paramecium produce 18 times as much ATP (36 vs 2 for e coli) since they are eukaryotes...

HOWEVER The explanation says "E. Coli are prokaryotes that lack mitochondria and can only use glycolysis for energy production."

Is this correct, E. Coli (specifically) cannot undergo aerobic respiration (because other bacteria can, in which case the net theoretical ATP yield would be 38ATP/ glucose) or does it have to do with no oxygen availability in the intestine...

I chose the answer saying that they both produce relatively equal amounts of ATP.

Can anyone clarify, thanks

E.coli is a facultative aerobe. It can undergo aerobic and anaerobic growth. I think the key to the question was the location of the E.coli i.e. in the intestine.

 

[notbobtrustme]

I was doing a Kaplan BS section tests and came across a question asking about ATP production in e coli living in the intestine vs a paramecium..

So, the correct answer was that paramecium produce 18 times as much ATP (36 vs 2 for e coli) since they are eukaryotes...

HOWEVER The explanation says "E. Coli are prokaryotes that lack mitochondria and can only use glycolysis for energy production."

Is this correct, E. Coli (specifically) cannot undergo aerobic respiration (because other bacteria can, in which case the net theoretical ATP yield would be 38ATP/ glucose) or does it have to do with no oxygen availability in the intestine...

I chose the answer saying that they both produce relatively equal amounts of ATP.

Can anyone clarify, thanks

wow, that's a terrible explanation. Many species of bacteria can aerobically respire; they can ferment and they can anaerobically respire (use another electron acceptor instead of O2, such as NO3-). In the context of the question, the intestines should have extremely limited O2 availability, forcing E. coli to ferment sugars for energy. Technically, E. coli produces 3 ATP while fermenting because it can sneak another ATP through production of H2 from glucose but that's beyond the scope of the MCAT.

 

[cycloethane]

I agree that this question is beyond the scope of the MCAT. However, on the real test you will be given questions which test simpler concepts in such a hard way that you will still be struggling just as you are right now... It is hard to explain. I took the test. It seems that it is important not to get overconfident just because the material tested on the real deal tends to be less advanced than what you have learned--the problems can still be tricky as hell.

 

[Morsetlis]

wow, that's a terrible explanation. Many species of bacteria can aerobically respire; they can ferment and they can anaerobically respire (use another electron acceptor instead of O2, such as NO3-). In the context of the question, the intestines should have extremely limited O2 availability, forcing E. coli to ferment sugars for energy. Technically, E. coli produces 3 ATP while fermenting because it can sneak another ATP through production of H2 from glucose but that's beyond the scope of the MCAT.

E. coli is a prokaryote.

Prokaryotes do not have mitochondria.

No mitochondrias = no oxidative phosphorylation, with O2 as the final e- acceptor in the electron transport chain.

Ingested Nitrates (NO3-) from vegetables/juices will be reduced as an e- acceptor to Nitrites (NO2-)

The point of the question was that no mitochondria = no oxidative phosphorylation, not what random facultative anaerobes can digest dietary nitrates that may or may not be present (and also stretching the definition of aerobic respiration since nitrates as far as I know do not come from the air, that's N2(g) in the air).

 

[Pre-Med Village]

E. coli is a prokaryote.

Prokaryotes do not have mitochondria.

No mitochondrias = no oxidative phosphorylation, with O2 as the final e- acceptor in the electron transport chain.

Ingested Nitrates (NO3-) from vegetables/juices will be reduced as an e- acceptor to Nitrites (NO2-)

The point of the question was that no mitochondria = no oxidative phosphorylation, not what random facultative anaerobes can digest dietary nitrates that may or may not be present (and also stretching the definition of aerobic respiration since nitrates as far as I know do not come from the air, that's N2(g) in the air).

I'm not sure you mean to say that mitochondria are necessary for oxidative phosphorylation. In E. coli the respiratory complexes have a lot of particular differences in the substrates utilized but the general principle is the same as as it is with eukaryotes, conversion of energy from NADH and FADH2 to ATP via electron transport with oxygen as the ultimate electron acceptor. The proton gradient for ATP synthase works across the plasma membrane, though, in aerobic bacteria. Decades ago it was thought that a specialized structure called a mesosome was necessary, an invagination of the plasma membrane to create an inner cytoplasmic space, but those were discovered to be artifacts of fixation prior to microscopy.

 

[Morsetlis]

I'm not sure you mean to say that mitochondria are necessary for oxidative phosphorylation. In E. coli the respiratory complexes have a lot of particular differences in the substrates utilized but the general principle is the same as as it is with eukaryotes, conversion of energy from NADH and FADH2 to ATP via electron transport with oxygen as the ultimate electron acceptor. The proton gradient for ATP synthase works across the plasma membrane, though, in aerobic bacteria. Decades ago it was thought that a specialized structure called a mesosome was necessary, an invagination of the plasma membrane to create an inner cytoplasmic space, but those were discovered to be artifacts of fixation prior to microscopy.

You'd have to give numbers for us to evaluate the relative efficiency of plasma-membrane proton-gradient ATP synthesis in E coli compared to inner mitochondrial membrane proton-gradient ATP synthesis in eukaryotes.

Note: I have never studied E coli. or prokaryotes before in my life. That Micro class is next year.

 

[Pre-Med Village]

You'd have to give numbers for us to evaluate the relative efficiency of plasma-membrane proton-gradient ATP synthesis in E coli compared to inner mitochondrial membrane proton-gradient ATP synthesis in eukaryotes.

Note: I have never studied E coli. or prokaryotes before in my life. That Micro class is next year.

The textbook MCAT answer is that an aerobic bacterium can produce 38 ATP per molecule of glucose metabolized versus 36 for a eukaryote, the difference deriving from the eukaryotic need for the electrons produced by the oxidative decarboylization of pyruvate to be shuttled into the mitochondrion. However, there is complexity in the eukaryotic answer deriving from the relative predominance at a given moment of the malate-aspartate shuttle mechanism versus the glycerol 3-phosphate shuttle, the latter being less efficient. Those distinctions in eukaryotes are treated in a portion of biochemistry which is more advanced than the MCAT.

There is also further complexity for both cell types in that these efficiencies are theoretical, i.e. not generally achieved. It's easy to imagine the extracellular environment playing a role in determining prokaryote efficiency, for example, having to do, I imagine, with the ability of the cell wall in different environments to protect a proton gradient from extracellular effects like varying pH or diffusion, but that is pure conjecture on my part.

In the context of this question, the key must be simply the anaerobic environment of the intestine, but then why would metabolism of the paramecium be privileged to function? I hesitate to question Kaplan which is a top shelf outfit, really excellent question writers, but e. coli are facultative anaerobes, so they are capable of aerobic respiration. This may simply be a question writer mistake, or there may be clues in the passage, because in a difficult oxygen environment some bacteria will be carrying out aerobic metabolism at the boundaries while others have shifted to fermentation. Mistakes happen sometimes even with the best MCAT prep materials.

 

[Morsetlis]

The textbook MCAT answer is that an aerobic bacterium can produce 38 ATP per molecule of glucose metabolized versus 36 for a eukaryote, the difference deriving from the eukaryotic need for the electrons produced by the oxidative decarboylization of pyruvate to be shuttled into the mitochondrion. However, there is complexity in the eukaryotic answer deriving from the relative predominance at a given moment of the malate-aspartate shuttle mechanism versus the glycerol 3-phosphate shuttle, the latter being less efficient. Those distinctions in eukaryotes are treated in a portion of biochemistry which is more advanced than the MCAT.

There is also further complexity for both cell types in that these efficiencies are theoretical, i.e. not generally achieved. It's easy to imagine the extracellular environment playing a role in determining prokaryote efficiency, for example, having to do, I imagine, with the ability of the cell wall in different environments to protect a proton gradient from extracellular effects like varying pH or diffusion, but that is pure conjecture on my part.

In the context of this question, the key must be simply the anaerobic environment of the intestine, but then why would metabolism of the paramecium be privileged to function? I hesitate to question Kaplan which is a top shelf outfit, really excellent question writers, but e. coli are facultative anaerobes, so they are capable of aerobic respiration. This may simply be a question writer mistake, or there may be clues in the passage, because in a difficult oxygen environment some bacteria will be carrying out aerobic metabolism at the boundaries while others have shifted to fermentation. Mistakes happen sometimes even with the best MCAT prep materials.

So you're saying that the rates are similar (with the exception of aspartate/aKG/glu shuttle versus Gly3P shuttle)... but then wouldn't the prokaryote only have 1 large plasma membrane versus the eukaryote with an invaginated mitochondria + crista, making for more surface area? That is, it can undergo [o]phosphorylation at a much faster rate if it had unlimited substrate.

I'm assuming the environment of the gut is anaerobic...

Fermentation will be extremely inefficient (I think 2 ATP per glucose), but then the ATP output of both e.coli and paramecium should be the same.

God now you're confusing me, and I just learned this stuff this week.

 

[Pre-Med Village]

So you're saying that the rates are similar (with the exception of aspartate/aKG/glu shuttle versus Gly3P shuttle)... but then wouldn't the prokaryote only have 1 large plasma membrane versus the eukaryote with an invaginated mitochondria + crista, making for more surface area? That is, it can undergo [o]phosphorylation at a much faster rate if it had unlimited substrate.

I'm assuming the environment of the gut is anaerobic...

Fermentation will be extremely inefficient (I think 2 ATP per glucose), but then the ATP output of both e.coli and paramecium should be the same.

God now you're confusing me, and I just learned this stuff this week.

The rates of eukaryotic versus prokaryotic oxidative metabolism haven't been mentioned one way or another. The issue is overall stoichiometric yields which are ideally 36 for eukaryotic cells versus 38 for aerobic prokaryotes from a single molecule of glucose.

The answer and explanation referenced in the original question seem to be incorrect.