Final answer:
The mitochondrion increases ATP through oxidative phosphorylation during the electron transport chain. A gradient of hydrogen ions powers ATP synthase to convert ADP to ATP, which is the main method for generating significant amounts of ATP in cells.
Step-by-step explanation:
The amount of ATP is increased inside a mitochondrion through a process known as oxidative phosphorylation, specifically during the electron transport chain (ETC) and chemiosmosis. This is not to be confused with glycolysis, which occurs in the cytoplasm, or the Krebs cycle, which does produce a small amount of ATP through substrate-level phosphorylation. Most of the ATP generated during the aerobic catabolism of glucose, however, comes from the electron transport chain, involving a series of redox reactions that create a concentration gradient of hydrogen ions. These ions flow through ATP synthase, which drives the phosphorylation of ADP to ATP, vastly increasing ATP yield.
During chemiosmosis, which is part of oxidative phosphorylation, the flow of hydrogen ions (protons) through ATP synthase is coupled with the phosphorylation of ADP to produce ATP. This process relies on the electrochemical gradient established by the ETC, which involves various electron carriers within the inner mitochondrial membrane. The potential energy stored in this gradient is what allows for the high-level production of ATP in mitochondria, hence its nickname, the 'powerhouse of the cell'.
It is important to note that while NADH generated during glycolysis and the Krebs cycle contributes to the ETC, it cannot easily enter the mitochondria. Instead, shuttle systems such as the Glycerophosphate shuttle and the Malate-Aspartate shuttle aid in transporting electrons into the mitochondria to partake in oxidative phosphorylation.