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Name: Megan M.
Status: Student
Age: 16
Location: N/A
Country: N/A
Date: 2001


Question:
In aerobic respiration in bacteria cells, how do the bacteria create a concentration gradient of H+? From what I understand, this type of bacteria are basically one giant mitchondrion. In an eukaryotic cell, H+ are pumped out of the mitochondria to form a concentration gradient. As the H+ travel down the gradient, the energy that is produced attaches a phosphate to ADP creating ATP.

I do not understand how a concentration gradient would be produced if the bacteria pumped H+ out of the cell into the "world".



Replies:
I got out my Microbial Physiology text from grad school! It says that in eukaryotic organisms these reaction take place in the inner membrane of the mitochondria but in prokaryotes it takes place in the cell membrane. I guess it can take place from inside to the outside.

vanhoeck


Megan, that is a good question, and you have the correct understanding of how it all works. But bear in mind that the concentration difference is only part of the story. In addition, for every H+ that is pumped out, the inside of the cell loses a positive charge, and becomes more negative relative to the outside world. So there is a charge difference between the inside and outside of the cell, which attracts the positive H+ ions back in via the complex that makes ATP.

PaulinMO


Dear Megan,

The answer lies in the bacterial cell wall. Protons are pumped toward the outside of the plasma membrane, but not "out of the cell into the 'world'". Instead, they enter the "periplasmic space" between the plasma membrane & the cell wall, so they can still drive oxidative phophorylation. The following tutorial from the ASM has an excellent animated diagram of the whole process:

http://www.microbelibrary.org/FactSheet.asp?SubmissionID=400

Thanks a lot for the great question,

Jeff Buzby, Ph.D.



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