What is the fate of Nicotinamide adenine dinucleotide (NADH) and Flavin adenine dinucleotide (FADH2) in the electron transport chain?

From the Guidelines

NADH and FADH2 are oxidized, donating electrons to the electron transport chain. During cellular respiration, these molecules serve as electron carriers that deliver high-energy electrons from earlier metabolic processes (glycolysis and the citric acid cycle) to the electron transport chain embedded in the inner mitochondrial membrane. As NADH and FADH2 donate their electrons, they are converted back to their oxidized forms (NAD+ and FAD), as described in the enzymatic assay for Complex I, where NADH is oxidized to NAD, transferring electrons to ubiquinone 1. The electron transport chain uses these donated electrons to pump protons across the membrane, creating an electrochemical gradient. This gradient drives ATP synthase to produce ATP through oxidative phosphorylation.

Key points about the electron transport chain and the role of NADH and FADH2 include:

• NADH and FADH2 are electron carriers that donate electrons to the electron transport chain
• The electron transport chain is embedded in the inner mitochondrial membrane
• The donation of electrons by NADH and FADH2 leads to the creation of an electrochemical gradient
• This gradient drives ATP synthase to produce ATP through oxidative phosphorylation
• NADH typically yields about 2.5 ATP molecules when its electrons flow through the chain, while FADH2 yields about 1.5 ATP molecules, as it enters the chain at a lower energy level, as can be inferred from the description of Complex I and Complex II activities 1.

The process of electron transfer from NADH and FADH2 to the electron transport chain is crucial for aerobic respiration and represents the final stage where most cellular energy is captured. The enzymatic assays described for the different complexes of the electron transport chain, including Complex I, Complex II, and Complex III, provide further insight into the mechanisms by which NADH and FADH2 donate electrons to the chain 1.

From the Research

Electron Transport Chain Process

• NADH and FADH2 are oxidized, donating electrons to the chain, as part of the electron transport chain process 2, 3, 4, 5, 6

Role of NADH and FADH2

• NADH and FADH2 collect electrons and transfer them through a series of electron carriers within multiprotein respiratory complexes to oxygen, generating an electrochemical gradient 3
• The electrochemical gradient is used by the F1-F0-ATP synthase to synthesize ATP 2, 3

Outcome of Electron Transport Chain

• The oxidation of NADH and FADH2 results in the generation of ATP through oxidative phosphorylation 2, 3, 6
• The process also leads to the production of reactive oxygen species (ROS) as a consequence of electron transfer 4, 6