Ask A Scientist Molecular Biology Archive

name         Megan M.
status       student
age          16

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".
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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
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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
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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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