Biology
Mitochondrial Function
Quick fact
Mitochondria have their own DNA, which is inherited exclusively from the mother, and mutations in this DNA can cause energy-related diseases.
Why this is interesting
You've heard mitochondria are the powerhouse of the cell—but how do they actually turn the food you eat into usable energy?
Read the full explanation
Understanding Mitochondrial Function
Mitochondria are double-membrane organelles found in nearly all eukaryotic cells. Their main job is to convert the chemical energy from nutrients into a form the cell can use: ATP (adenosine triphosphate). Think of ATP as a rechargeable battery that powers cellular work. The process begins when breakdown products from glucose and fats enter the mitochondria. Inside, the Krebs cycle produces high-energy electrons, which are then passed along a chain of proteins embedded in the inner mitochondrial membrane. As electrons move down this chain, they pump protons across the membrane, creating a gradient—like building up water behind a dam. The flow of protons back through a molecular turbine called ATP synthase spins a rotor, attaching a phosphate to ADP to make ATP. This elegant system is called oxidative phosphorylation because it uses oxygen as the final electron acceptor, producing water as a byproduct.
A deeper explanation
The mechanism of mitochondrial function hinges on the electron transport chain and chemiosmosis. Four protein complexes (I–IV) in the inner membrane transfer electrons from NADH and FADH₂ to oxygen, each step releasing energy used to pump protons out of the matrix. This creates a high proton concentration in the intermembrane space, generating an electrochemical gradient. ATP synthase (complex V) allows protons to flow back inward, and the energy of this flow drives the synthesis of ATP—over 30 molecules per glucose molecule. Beyond energy production, mitochondria are central to apoptosis: the release of cytochrome c triggers programmed cell death. They also buffer calcium ions and generate heat in brown fat by uncoupling the proton gradient. Without mitochondria, efficient energy production would be impossible, linking their function to everything from muscle contraction to brain activity. Disruptions in mitochondrial function are implicated in aging, neurodegenerative diseases, and metabolic disorders.