Oxygen to H20 is ETC mechanism

[RH8448]

Oxygen is a linear molecule and nonpolar. This means it diffuses into the cell membrane and the mitochondrial membranes. Oxygen has a negative charge. Why would oxygen want to have more electrons from the ETC? I understand that it is used to make water. Does the o2 split to form to superoxides?

What do the electrons attach to during the ETC and how? Are hydrides involved? How many electrons does it take to make one water molecule?

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[sazerac]

You can follow the exact biochemistry in a biochem textbook, or see the "Biochemistry" subsection of Cytochrome c Oxidase here:

http://en.m.wikipedia.org/wiki/Cytochrome_c_oxidase

I was about to say that this is beyond the scope of the MCAT, but I have no idea what they are testing now in 2015, what with this biochemistry requirement. Back in my day, knowing that O2 had 16 electrons, but two molecules of water had 20 electrons (and four extra H+ ions) was good enough. Everything else would be explained in the passage.

 

[sazerac]

Oxygen has a negative charge.

You are treading on thin ice here. Do you mean oxygen the molecule? That's neutral. Do you mean oxygen the atom? It's neutral too, though highly electronegative. Do you mean oxygen the superoxide ion? Well yes that is negative, but we haven't established that superoxide plays a role here. Besides, that's not really oxygen anymore.

 

[Czarcasm]

It's my understanding that molecular oxygen (O2), which is nonpolar, simply diffuses through the lipid membrane and into the cell, towards the mitochondrial matrix. From there, the last cytochrome of the ETC passes two electrons to molecular oxygen, giving it a -2 overall charge. Shortly thereafter, oxygen picks up 2 protons (H+) to produce water. Essentially, this uses 1 oxygen in the process (ie. 1/2 O2), but the other oxygen is quickly used thereafter. Occasionally however, some radicals are produced in the process and these radicals can damage our cells. Thankfully, our cells produce antioxidants like glutathione to help eliminate and reduce free radicals that could otherwise destroy crucial information, like our DNA or plasma membranes.

 

[RH8448]

Thank you for the explanations. Is it accurate to say that O2 as a paramagnetic molecule will very much want to take 2e- to fill its orbitals so that they become diamagnetic?