Concept 1 Review

A Closer Look: Electron Carriers

A number of molecules can act as electron carriers in biological systems. In cellular respiration, there are two important electron carriers, nicotinamide adenine dinucleotide (abbreviated as NAD+ in its oxidized form) and flavin adenine dinucleotide (abbreviated as FAD in its oxidized form). The NAD+ molecule is used to accept electrons (becomes reduced) in several chemical reactions in glycolysis and the Krebs cycle. NAD+ accepts a hydrogen ion (H+) and two electrons (2e), as it becomes reduced to NADH + H+. The NADH moves to the electron transport chain and donates a pair of electrons (becomes oxidized) to the first compound in the chain. The oxidation of NADH to NAD+ results in the liberation of 53 kcal/mole (under standard conditions).

To see the process, point to the image below.

Energy and ATP

As you move your mouse over the image, a hydrogen and two electrons are added to form NADH, and removed to form NAD+.