Energy and Metabolism

ID #2203

I don't understand what the point of reducing NAD+ to NADH in glycolysis is? I don't understand how it is an electron carrier and what its function is, and why it is necessary to replenish the NAD+ molecules?

Prof Mehrtens mentioned in lecture 9 the three possible things that we might do with the energy released from catabolic reactions: (1) use it right away; (2) harness the energy and use it later; and (3) lose it as heat. Obviously, we want to minimize option (3), so we break down glucose in a series of steps. The carbon and hydrogen molecules in glucose undergo a series of oxidation steps in order to squeeze out its energy, and this involves the removal of electrons. Since electrons are a form of energy, they are harnessed by transferring the electrons to a molecule (NAD+) that accepts them. We refer to this as a coupled redox reaction.

The analogy for NAD+ used in class is the UPS truck/courier. They will take a package and deliver it to a final destination. In the same manner, NAD+ takes the electrons from oxidized molecules (gets reduced to NADH). The finite supply of NAD+ is used up in these reactions, so it is necessary to regenerate the NAD+ either through the ETC or via fermentation. In either case, NADH delivers the electrons to an electron acceptor and gets oxidized back to NAD+. Only by recycling NAD+ can the cell continue another cycle of cellular respiration. 

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