Stupid Bio... redox help needed.

Factual Questions
1

Ok so I understand redox reactions in the context of chemistry, but in bio they seem to be doing something different.

First question:
the following reaction:
C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] + 6O[sub]2[/sub] -> 6CO[sub]2[/sub] + 6H[sub]2[/sub]O

THe book says “glucose is oxidized to carbon dioxide, while the oxygen is reduced to water”… I’m not following this at all. From the chemistry I’ve gone through so far, individual atoms or ions are oxidized and reduced and it’s fairly easy (though somewhat tedious) to figure out which was which. So by what definition of oxidation and reduction can you say some reactant was oxidized into a product which is part reactant A and part reactant B?

Second question (along the same lines probably):
Lecturer says:
“Glucose is oxidized to pyruvic acid. We should be able to figure this out easily because if NADH is produced, those hydrogen atoms had to come from somewhere.”
So um… is the definition of redox in this case the transfer of hydrogen atoms? The removal of hydrogen atoms from a reactant constitutes oxidation?

Ok so I can maybe wrestle through those… but this one is really confusing me:
After glycolysis…pyruvate, C[sub]3[/sub]H[sub]3[/sub]O[sub]3[/sub], enter the mitochondrion… CO[sub]2[/sub] is removed so now the molecule is C[sub]2[/sub]H[sub]3[/sub]O…Then it says “The remaining two-carbon fragment is oxidized to form a compound named acetate. An enzyme transfers the extracted electrons to NAD+, storing the energy in the form of NADH.” So what exactly is taken off the C[sub]2[/sub]H[sub]3[/sub]O to form NADH out of NAD+? The standard reduction of NAD+ requires two Hydrogen atoms, so I would assume it would have to take two H’s off the molecule. Perhaps because there are extra electrons left on the molecule, it can reduce NAD+ without 2 H’s…but in order to form NADH there must be at least one H added right? Only problem is after this oxidation, all 3 H’s are supposedly still on the molecule.

What am I missing?

please help…trying to study and hit a road block.

2

So by what definition of oxidation and reduction can you say some reactant was oxidized into a product which is part reactant A and part reactant B?
Consider: oxidition is the loss of electrons, reduction is the gain of electrons. You can also think of the reaction is terms of the # of bonds to Oxygen. An oxidation reaction increases the bonds to oxygen, a reduction reaction loses bonds to oxygen (and, frequently, gains them to hydrogen.) Here, the glucose molecule is taken through a number of steps to a point wherein each carbon from glucose contains bonds only to oxygen. Therefore, glucose is oxidized. But you can’t have oxidation without having a reduction; the electrons must be transferred somewhere. In this case, to the oxygen.

is the definition of redox in this case the transfer of hydrogen atoms? The removal of hydrogen atoms from a reactant constitutes oxidation?
Yes. If you look at the individual steps of glycolysis, you’ll note that for every H lost from a reacting carbon, a bond to phosphorus or oxygen is usually formed.

**So what exactly is taken off the C2H3O to form NADH out of NAD+? **
When the CO[sub]2[/sub] is removed, it leaves a two-carbon fragment that is unstable. This two-carbon fragment is oxidzed, i.e., loses electrons to NAD+ and gains a bond to oxygen. (Remember, this reaction only occurs in the presence of O[sub]2[/sub].) This is the acetate molecule.

I hope that helps a bit.