Re: How does Coenzyme Q pump protons across the mitochrondria membrane?

Hi Angel,
Coenzyme Q, also called Ubiquinone, is one of a group of proton/electron carriers. They are all similar in that they have two ketone groups which can each react with a proton and an electron to be converted into an alcohol functional group. The reaction takes place inside of an enzyme. There are several enzymes that use quinones to transfer electrons and protons. One of them is the cytochrome bc1 complex of mitochondria. Several others are involved in photosynthesis. In some photosynthetic bacteria, the bc1complex is used not only for respiration, but also in photosynthesis.

The carriers themselves are not proteins. They are hydrophobic aromatic compounds that float around randomly in the lipid membrane of the cell or organelle that they function in.

Here's a link a page hosted by the lab of Dr. Tony Crofts, where I work. We do research on the cytochrome bc1 complex. There are diagrams showing the structure of the bc1 complex and how it functions in photosynthetic bacteria.

http://www.life.uiuc.edu/crofts/bioph354/bc-complex_summary.html

Here's a page showing a diagram of how ubiquinone ferries electrons and protons between the cytochrome bc1 complex and the bacterial photosynthetic reaction center.

http://ahab.life.uiuc.edu/qcycle1.html

Here's a picture of Ubiquinone:

http://www.life.uiuc.edu/crofts/bioph354/uq.html

And the online course in bioenergetics which hosts that picture is at:

http://www.life.uiuc.edu/crofts/bioph354/

Well, that should be enough to get you started. Bioenergetics is a fascinating field and you should be able to find just about everything that is known about the bc1 complex and quinones by following the links on these pages. If you find you can't sate your curiosity here, perhaps you should think about a career in bioenergetics. Good luck. Who knows, maybe I'll hear you giving a lecture at a conference some day.

Sincerely,
Todd Holland
Mad Scientist and Biophysics Graduate Student
Tony Crofts Lab
University of Illinois at Urbana-Champaign