What is the main contribution of mitochondria to a eukaryotic cell?

Core Concept

The inner mitochondrial membrane houses the electron transport chain and ATP synthase, which convert energy released from NADH and FADH2 into a proton gradient that powers oxidative phosphorylation. This chemiosmotic machinery supplies the bulk of ATP in aerobically respiring cells. Glycolysis in the cytosol yields some ATP as well, but the mitochondrial stages raise the harvest dramatically.