The night before the exam, one story changed everything.

Mitochondria are the energy factories of every cell in the human body. They convert glucose and oxygen into adenosine triphosphate (ATP) through a process called cellular respiration. The inner membrane of each mitochondrion is folded into cristae, increasing the surface area available for the electron transport chain. Protons are pumped across this membrane, creating an electrochemical gradient. ATP synthase harnesses this gradient like a molecular turbine, spinning to produce ATP molecules. A single cell can contain thousands of mitochondria, and they carry their own DNA — inherited exclusively from the mother. When mitochondria malfunction, the consequences range from muscle weakness to neurodegeneration. Exercise increases mitochondrial density and efficiency, which is why regular physical activity improves energy levels at the cellular level. Understanding mitochondria is understanding how life pays its energy bills.