Final answer:
ATP synthesis in the mitochondria occurs through oxidative phosphorylation, where ATP synthase generates ATP from ADP and phosphate using a proton gradient created by electron transport chains.
Step-by-step explanation:
When ATP is synthesized in the mitochondria, it occurs by a process known as oxidative phosphorylation. This involves electrons moving through a series of carriers in redox reactions, creating a concentration gradient of hydrogen ions. This gradient powers the ATP synthase, an enzyme that facilitates the transformation of adenosine diphosphate (ADP) and phosphate (Pi) into ATP. By utilizing a chemiosmotic mechanism, which was famously elucidated by Peter Mitchell (Nobel Prize in Chemistry, 1978), oxidative phosphorylation effectively captures free energy from the mitochondrial proton gradient. This is a critically efficient method of producing ATP during the aerobic catabolism of glucose, responsible for generating approximately 90 percent of the ATP from this process.