PH and the mitocondria

direw0lf, BSN · Oct 21, 2015

My first thought was no. I'm going to ask someone who's a chem genius and get back to this though. Here's some more thoughts though: What is the pH in the mitochondrial matrix and why? | Student Doctor Network

oldsockventriloquist · Oct 21, 2015

I have had 6 total profs. with my prereqs and none of them were able to answer a question I asked them, so I was wondering if anyone here would want to give a go at it. I won't go through the whole electron transport thing, and just assume everyone is familiar with it. At the end there are hydrogen ions in the mitochondria, do the presence of those ions make the mitochondria acidic?
I have no idea on the answer, and with little time I have I haven't felt like studying things I don't need to know. Just curious if anyone out there does know.

So, the mitochondria, which is the energy powerhouse of the cell, has two membranes: the outer membrane and inner membrane. Those membranes are separated by the intermembrane space. Past the inner membrane, more towards the center of the mitochondria, is the matrix. So basically (skipping over some steps) electron carriers, meaning they carry hydrogen atoms which can give off electrons, arrive from being produced in glycolysis and then Kreb's cycle, two metabolic processes. Those electron carriers release those hydrogen atoms from the matrix that goes through the inner membrane and into the intermembrane space. Because that creates a high concentration of hydrogen ions (remember they gave up an electron) within the intermembrane space, the intermembrane space will have a low pH, or be acidic.

Once enough hydrogen ions have built up on the intermembrane space side, a great enough hydrogen concentration difference will be created between that space and the matrix, that a gradient will be created through ATP synthase that uses the natural flow of hydrogen atoms back into the matrix to create energy (think of a water turbine, where the water is hydrogen ions). Because these hydrogens return to the matrix, it will decrease the pH of the matrix. However, the overall pH of the mitochondria matrix will be higher than 7 and it will be basic. So in summary, it depends on which part of the mitochondria you are talking about. The mitochondrial intermembrane space is acidic, while the mitochondrial matrix is basic. The whole description above gives an overly simplified version of the electron transport chain. Hopefully, this helps.

Just as an added bonus, the final electron acceptor of those hydrogen electrons is oxygen (O2). This shows why oxygen is important and why competitors of oxygen, like carbon monoxide, can be so dangerous.

Here are some actual pH values: pH difference across the outer mitochondrial membrane measured with a green fluorescent protein mutant

Here's a link showing how it all works: https://en.m.wikipedia.org/wiki/Electron_transport_chain