i dont understand chemiosynthesis. help?

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i dont understand chemiosynthesis. help?

Post by csin » Mon Mar 20, 2006 5:47 am

hi i am new to this forum and im studying for a cellular respiration exam. so far i understand everything except for chemiosmosis. my textbook doesnt really talk about it, except for that hydrogen and its electrons are taken by NAD and FAD in glycolosis, transition and the kreb cycle and how the NAD and FAD gives up the hydrogen and electrons to cytochrome enzymes and the cytochrome enzymes gives the H and E- to oxygen, the final acceptor, from there i am stuck. can anyone help to explain chemiosmosis? ive tried searing the forums other websites.

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Post by MrMistery » Mon Mar 20, 2006 7:12 pm

Chemiosmosis reffers to storing energy under the form of a proton gradient. I will only explain the mechanism, and it is then up to you to look at the details in a book or online.
In glicolisys and the krebs cycle only 6 molecules of ATP are produced, by sustrate-level phosphorilation. The main energy is taken over under the form of energised electrons by these electron acceptors: NAD+ and FAD.
In the process called oxidative phosphorilation, the synthesis of ATP is done on the expense of the energy stored in these molecules.
The NAD+ or FAD molecule gives it's electron to a molecule, known as an electron acceptor. THis is a redox reaction. This newly energised molecule gives the electron to another molecule, which has a bigger redox potential, and electron affinity, than the first one. This is done several times in a chain of molecules, and the last electron acceptor is oxygen. This is what is known as the electron transport chain. The process is completely dependent of Oxygen. In the absence of oxygen, there is nothing to pull the electrons down the electron transport chain.
You can imagine it like a ball falling down some stairs, losing potential energy every time it gets to a lower level. But unlike the situation with the ball, the energy is not lost in the electron transport chain. The cell uses it to pump protons in the space between the 2 membranes of the mithocondria. For every NADH molecule, about 10 protons are pumped from one side of the inner membrane to the other. FADH2 pumps less protons because it gives it's electron lower in the electron transport chain.
While this is done, a proton gradient builds up between the intermembrane space and the citoplasm, so the H+ ions try to diffuse back into the cytoplasm along their electrochemical gradient. But the only place they can cross the membrane are special proteins within the membrane, named F0f1-ATP synthase. This enzyme is a modified ion pump that instead of using ATP to pump things against their concentration gradient uses the diffusion of protons to phosphorilate ADP and Pi into ATP. To make one ATP molecule, the ATP synthase uses 4-5 H+ ions.

And is a summary... For more info, see this site: http://www.ncbi.nlm.nih.gov/books/bv.fc ... id=mcb.TOC
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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