NADH is used for oxidative metabolism. NADH is used for catabolic
pathways. In the citric acid cycle you use NAD+ as an electron carrier
for the three of the reactions. NAD+ grabs the electrons from the
metabolite and is converted to NADH + H. NAD+ wasn't there to take the
electrons from the reaction the citric acid cycle could very well stop
because you need those electrons picked up to make the next metabolite
so the next metabolite can be converted. The NADH + H goes to the
electron transport chain (ETC) and donates the electrons to Complex I.
It's used for fatty acid-breakdown in the same way, NAD+ takes the
electrons from an H-C-OH group to make it a C=O group.
However, NADH can also be used as an electron donor such as the electron
transport chain or when lactate is converted back to pyruvate.
NADPH is used for reductive metabolism. NADPH is used for anabolic
reactions. NADPH is used for biosynthesis. NADPH is used as reductive
power in pathways such as cholesterol synthesis and fatty acid
synthesis. The way that helped me learn this at first was that while
NADH was for electrons, NADPH was used for the hydrogens for reactions
such as reducing a double bond, CH=CH to CH2-CH2; or it can reduce a C=O
to CHOH or CH2OH. Once, I learned it that way it was much easier to
separate the two concepts.
Dec 20th, 2014
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