[poobear]

I have read that chloroplast uses a proton gradient to move its ATP Synthase, while the mitochondria mostly uses an electrochemical gradient.
Does this mean that besides the proton gradient, the inner membrane space and the outer membrane space of the mitochondria is filled with ions of opposite charge? And this would make the charged protons wanna move faster to the opposite side.

Meanwhile, the thykaloid lumen and stroma would not be filled with ions of different charge, since the impact of electrochemical gradient is very low in the chloroplast.

Is this solution right?

/ Thanks
Just registrated myself to this awesome forum

[Yggdrasil]

Bot chloroplasts and mitochondia use a proton gradient to power ATP synthesis.  Also, a proton gradient is an electrochemical gradient.  A chemical gradient is the imbalance of a chemical species on either side of the membrane (in this case protons).  An electrical gradient is an imbalance of charge on either side of the membrane.  Pumping protons across the membrane creates both a chemical gradient and an electrical gradient (since protons are charged), so the resulting gradient is referred to as an electrochemical gradient.

[poobear]

Yes, I realize that a proton gradient is also a electrochemical gradient.
What I fail to understand though is this statement:
"Chloroplast uses a proton gradient to rotate its ATP Synthase, while the mitochondria uses alittle of the proton gradient but mostly the electrochemical gradient".
My solution to this problem was that besides the different amount of protons on the two sides of the membrane, the mitochondria also have a different amount of charged ions (besides H+) on the two sides. Thus creating an even bigger electrochemical gradient that makes the protons wanna move even more.
Is that correct? Or do they just e.g. have different ATP Synthases that work differently?

/ Thanks

[Arkcon]

I've always understood it exactly as Yggdrasil: explained it, that the mitochondrial ATP synthetase worked using a proton gradient -- the transfer of H+ through the "lollypop" synthetase is what drives phosphorlation of the ADP by inorgainic phosphate.  I wasn't aware of the electrochemical gradient you mentioned, but it may be there, and I don't really understand the quote.  However, your statement:

Thus creating an even bigger electrochemical gradient that makes the protons wanna move even more.

Doesn't really follow logically.  You don't get more ATP because the H+ "want" to move more.  As I recall, you get one ATP per H+ transferred.

[spirochete]

The OP might be referring to the fact that advanced books identify two different parts to the chemiosmotic gradient present in mitochondria and chloroplasts. 

 One part is referred to as delta psi, aka the "charge" gradient.  The other is the chemical gradient.  Moving an uncompensated charge like a naked proton creates delta psi, moving a compensated charge creates a chemical gradient.   

Unfortunately I never fully understood how it worked.  If anybody knows please chime in.

[Yggdrasil]

poobear: If there are more other positive ions (e.g. Na⁺, K⁺) in the intermembrane space than in the matrix, then you are correct that the proton motive force would be greater than if there were not an imbalance of these other cations.  I'm not sure whether it is true that there is an imbalance of other cations across the mitochondrial inner membrane, but I wouldn't discount the possibility.

[sergei_DSc]

I have a question related to this: Why is it that the electrochemical gradient is maintained in the intermembrane space even though the outer mitochondrial membrane allows free diffusion of ions??
I havent had time to thoroughly research the specificity of porins, but a biochemistry reference book I have mentions that the porins on the outer mitochondrial membrane allow free diffusion of ALL molecules under 5kDa. This has to be a mistake because a gradient would be impossible if this is so.

[Yggdrasil]

The gradient occurs because the proton pumps change the hydrogen ion concentration of the matrix.  Because the mitochondrial outer membrane is permeable to the cytoplasm, pumping protons from the matrix to the intermembrane space does not appreciably change the hydrogen ion concentration of the intermembrane space.

[sergei_DSc]

Thank you, that makes sense.