pH in the mitochondria

[dontbeanegaton]

Question 10 of the Kaplan FL 6 asks what will happen if a mitochondrion kept in pH 8 is moved to pH 4 solution.
Since the acidity outside the mitochondria doesn't matter for the gradient, I answered that there would be no change in ATP production.
However, the correct answer is that there would be a boost in the ATP production. Does the intermembrane space always match the pH of the cytoplasm? How does dropping the mito into acid cause a drop in pH in the i.m. space?

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[ToldYouSo]

The outer membrane is permeable to ions, so in a low pH environment the intermembrane space will have a high [H+], leading to ATP production

 

[StIGMA]

The electron transport chain on the inner mitochonrial membrane pumps protons OUT of the center. These protons (eg: the same effect of a lower pH) pump back into the mitochondrial matrix through ATP synthase via the gradient.

The intermembrane space as you call it mimics the pH of the cytoplasm because it is contiguous with the cytoplasm- there are large pores on the outer mitochondrial membrane. These pores do no exist on the inner membrane, and protons thus travel through ATP synthase on the inner membrane, generating ATP.

If the pH was drastically lowered (increasing proton concentration drastically on the outside of the inner mitochondrial membrane), there would be an enormous gradient favoring ATP production. Eventually this gradient would dissipate.

 

[ToldYouSo]

The electron transport chain on the inner mitochonrial membrane pumps protons OUT of the center. These protons (eg: the same effect of a lower pH) pump back into the mitochondrial matrix through ATP synthase via the gradient.

The intermembrane space as you call it mimics the pH of the cytoplasm because it is contiguous with the cytoplasm- there are large pores on the outer mitochondrial membrane. These pores do no exist on the inner membrane, and protons thus travel through ATP synthase on the inner membrane, generating ATP.

If the pH was drastically lowered (increasing proton concentration drastically on the outside of the inner mitochondrial membrane), there would be an enormous gradient favoring ATP production. Eventually this gradient would dissipate.

^ A much better explanation than mine! XD

 

[dontbeanegaton]

The electron transport chain on the inner mitochonrial membrane pumps protons OUT of the center. These protons (eg: the same effect of a lower pH) pump back into the mitochondrial matrix through ATP synthase via the gradient.

The intermembrane space as you call it mimics the pH of the cytoplasm because it is contiguous with the cytoplasm- there are large pores on the outer mitochondrial membrane. These pores do no exist on the inner membrane, and protons thus travel through ATP synthase on the inner membrane, generating ATP.

If the pH was drastically lowered (increasing proton concentration drastically on the outside of the inner mitochondrial membrane), there would be an enormous gradient favoring ATP production. Eventually this gradient would dissipate.

Thanks! Didn't know the outer membrane was porous.