Biology - oxidation/reduction terminologies

[Monkeymaniac]

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The usage of some terminologies involved in oxidation/reduction have been bogging me for a long time. I'd appreciate if someone could please take a peek at it.

1) I see phrases like "Reduced molecules such as carbohydrates and fats are oxidized to produce CO2 and ATP." Here, it's talking about molecules being oxidized or reduced. But I've also seen something like "There are several ways to oxidize or reduce an atom." Here, they are used to describe an atom.

If we're talking about a small molecule, where only one atom is oxidized (say C of R-CH2-OH to R-C=O), I guess we can say that the entire molecule is oxidized. But I think there might be a problem for a large molecule, which has multiple reduction/oxidation sites such that, say n number of atoms get oxidized and m number of atoms get reduced at the same time. In this case, how do we know if the molecule got oxidized or reduced?

2) Why do we say that macromolecules get oxidized to provide for energy? Is it beacuse during aerobic respiration, carbons of a glucose get converted to CO2, which a carbon has a high oxidation state compared to when they were part of the glucose? Thanks in advance.

 

[bxadook]

Usually in inorganic chemistry whenever an oxidation/reduction reaction is performed, the individual oxidation state of the atoms gets changed. Like in the case of this reaction:

Zn(s) + 2HCl(aq) ---> ZnCl2 + H2

Zinc gets oxidized from a neutral oxidation state to +2. Hydrogen gets reduced from a +1 oxidation state to 0. This is how atoms gets oxidized/reduced. Remember the two different ways oxidation and reduction can be interpreted in either organic or inorganic chemistry. In knowing if the molecule is oxidized or reduced in organic chemistry, either look at the reagents or look at the chemical structure. If you notice a change in O or H atoms, you could infer from there.

In terms of metabolism and oxidation, catabolic processes usually involve oxidation (Beta-oxidation of fatty acids in the liver with peroxisomes for instance). During this process the substrate has been oxidized by a oxidizing agent such as NAD+ or NADP+. This results in a net gain in O atoms, and a net decrease in H atoms on the substrate. And through various phosphorylations and dephosphorylations energy is liberated from the molecule.

And yes, they refer to glucose being oxidized to CO2, because it is one of the products of aerobic respiration and because it is the most oxidized form of carbon.


Hope this helps 👍

 

[Phantastic]

One further thing I would like to add is that in all chemistries, we are merely being electron psychologists. Oxidation and reduction just explain the behaviors of electrons, as they move from one energy carrying molecule to the next, until they can be used (either by creating a gradient, or directly in synthesis).

So, for biology, glucose starts with alot of energy (electrons), and we eventually move those through NAD+ (as NADH, remember, H+ is proton with no electrons, H is proton + electron) and various other electron carriers (for aerobic, electron transport chain). Again, just watching the electrons.

 

[Fifty 3rds]

Phantastic,

I love the way you word things. Very well said.

OP,

Shortcut is to look for Oxygens being added or taken away, although this isn't fail-proof. Phantastic said it much better, if you have time, that is a great way to understand.