Mitochondrion

A double-membrane-bound organelle with a relatively smooth outer membrane and an extensively folded inner membrane. The folds, called cristae, increase the surface area for the electron transport chain and ATP synthase. The matrix contains enzymes for the link reaction and Krebs cycle, mitochondrial DNA and ribosomes. The intermembrane space lies between the two membranes.

Major site of aerobic respiration in eukaryotic cells. The link reaction and Krebs cycle occur in the matrix. Electron transport in the inner membrane pumps protons into the intermembrane space. Protons flow through ATP synthase to drive ATP synthesis (oxidative phosphorylation). Oxygen is the final electron acceptor, forming water. Glycolysis occurs in the cytosol, not inside the mitochondrion.

Most eukaryotic cells, including plant and animal cells. Mature mammalian red blood cells are an exception.

Transfers energy released from organic molecules into ATP, the cell's main immediate energy carrier. ATP supports processes such as active transport, biosynthesis, movement and cell division. In many aerobically respiring eukaryotic cells, mitochondria generate most of the ATP.

Cristae increase the surface area of electron transport chains and ATP synthase. Inner membrane maintains proton gradient driving ATP production.