Mitochondria

Mitochondria are membrane-bound organelles in eukaryotic cells that carry out major parts of aerobic energy metabolism. The singular form is mitochondrion. Their best-known function is producing adenosine triphosphate, or ATP, through oxidative phosphorylation, converting energy released from nutrients into a chemical form that cells can use .^1,2

Each mitochondrion is enclosed by an outer membrane and a highly specialized inner membrane, with an intermembrane space between them and a central compartment called the matrix. The inner membrane folds into structures called cristae. Protein complexes of the electron transport chain transfer electrons, and several of these complexes use the released energy to move protons across the inner membrane. The resulting electrochemical gradient then drives ATP synthase, which produces ATP from ADP and inorganic phosphate .^1,2

The mitochondrial matrix contains enzymes involved in metabolic pathways such as the citric acid cycle. Mitochondria also contain their own DNA and machinery for expressing some of that genetic information. In humans, mitochondrial DNA encodes 13 proteins involved in oxidative phosphorylation, while the great majority of mitochondrial proteins are encoded by nuclear DNA, synthesized outside the mitochondrion, and imported into it .^1,2

Mitochondria are dynamic rather than permanently fixed structures. They can divide and fuse and may form interconnected networks within cells. Their characteristic combination of two membranes, specialized energy-converting machinery, and a small separate genome distinguishes them from most other cellular organelles .¹