Deepa100

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Why does my TPR book say that the inner mitochondrial matrix is impermeable to H+ ions? Isn' the whole proton gradient establishment for oxidative phosphorylation based on pumping H+ out of the matrix and then allowing them to drop back into the matrix?
 

Vihsadas

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Why does my TPR book say that the inner mitochondrial matrix is impermeable to H+ ions? Isn' the whole proton gradient establishment for oxidative phosphorylation based on pumping H+ out of the matrix and then allowing them to drop back into the matrix?
It is...but this happens in an active manner. If the membrane itself was permeable to H+ ions, then the H+ gradient would be dissipated before ATP Synthase could use that gradient to make ATP. It's kind of a 'semantical' question because in other contexts in biology you count transporters when you are considering the 'permeability' of an ion. (Think Na+ conductance when considering resting membrane potential.)

So is the IMM permeable to H+? Well...yes and no. The membrane itself (i.e. the lipid backbone) is not permeable. But H+ can travel from IMS to matrix via ATP synthase, and from matrix to IMS via the ETC (though the ETC H+ translocation mechanism itself is not well understood).
 

Kaustikos

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It is...but this happens in an active manner. If the membrane itself was permeable to H+ ions, then the H+ gradient would be dissipated before ATP Synthase could use that gradient to make ATP. It's kind of a 'semantical' question because in other contexts in biology you count transporters when you are considering the 'permeability' of an ion. (Think Na+ conductance when considering resting membrane potential.)

So is the IMM permeable to H+? Well...yes and no. The membrane itself (i.e. the lipid backbone) is not permeable. But H+ can travel from IMS to matrix via ATP synthase, and from matrix to IMS via the ETC (though the ETC H+ translocation mechanism itself is not well understood).
It makes sense. You have to use transport pumps and can't go through the membrane. If it wasn't for that, the gradient would never be set and you'd never be making ATP.

H+ only travels through by either the ETC or ATP synthase in the IMM.
 

bluemonkey

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Some chemicals (eg DNP) serve as carriers of protons across the IMM effectively dissipating the proton gradient. While the ETC keeps churning along, the protons pumped into the intermembrane space are shuttled back into the matrix on DNP. This further illustrates the importance of the impermeability of the IMM to protons. Believe it or not, people used to use this stuff as a dieting aid!
 

Kaustikos

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Some chemicals (eg DNP) serve as carriers of protons across the IMM effectively dissipating the proton gradient. While the ETC keeps churning along, the protons pumped into the intermembrane space are shuttled back into the matrix on DNP. This further illustrates the importance of the impermeability of the IMM to protons. Believe it or not, people used to use this stuff as a dieting aid!

HEY! That's supposed to be my monologue!:mad:


jk

And people still use it today; some pharmaceutical companies are actually playing with it to this day.:eek:
 

eikenhein

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Why does my TPR book say that the inner mitochondrial matrix is impermeable to H+ ions? Isn' the whole proton gradient establishment for oxidative phosphorylation based on pumping H+ out of the matrix and then allowing them to drop back into the matrix?
The membrane is impermeable, which allows a gradient to be established. But there is a channel associated with ATP-synthase that allows H+ to flow back in.
 
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Deepa100

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Thanks, I tend to think in absolute, back and white terms. That's my problem.
 

bluemonkey

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HEY! That's supposed to be my monologue!:mad:


jk

And people still use it today; some pharmaceutical companies are actually playing with it to this day.:eek:
Let's be sure to coordinate next time!