What is the first step that occurs in the electron transport chain?

The first step in the electron transport chain involves electrons being donated by NADH and FADH2 to proton pump enzymes. This donation is crucial because these reduced coenzymes, which are generated during earlier stages of catabolism such as glycolysis and the citric acid cycle, contain high-energy electrons.

When NADH and FADH2 donate these electrons to the electron transport chain, they enter a series of proteins, such as complex I (NADH dehydrogenase) for NADH and complex II (succinate dehydrogenase) for FADH2. This transfer of electrons initiates a cascade of redox reactions that leads to the subsequent pumping of protons across the inner mitochondrial membrane. This creates an electrochemical gradient that will later be used to generate ATP.

The process of donating electrons from NADH and FADH2 is fundamental to the chain's operation, as it sets in motion the entire process of oxidative phosphorylation. Understanding this initial step is essential for grasping the mechanics of cellular respiration and energy production.