Final answer:
The reduced carriers NADH and FADH2 deliver electrons to the electron transport chain, releasing energy used to pump protons and create an electrochemical gradient. Hydrogen ions return through ATP synthase, where their flow drives the synthesis of ATP - a process known as chemiosmosis.
Step-by-step explanation:
The energy stored in reduced carriers such as NADH and FADH2 is used in the process of oxidative phosphorylation, which occurs in the mitochondria of cells.
These reduced carriers donate electrons to the electron transport chain (ETC), which transfers the electrons through a series of redox reactions.
With each transfer, a little bit of energy is released, which is harnessed to pump hydrogen ions (protons) across the inner mitochondrial membrane from the matrix to the intermembrane space.
This active transport builds up a proton gradient, creating both a concentration gradient and an electrical charge difference, also known as an electrochemical gradient.
As hydrogen ions flow back down their electrochemical gradient through the ATP synthase enzyme, the flow of protons provides the necessary energy to synthesize ATP from ADP and inorganic phosphate (Pi).
This mechanism of ATP production powered by the flow of protons down their electrochemical gradient is termed chemiosmosis.
The ATP thus generated is a high-energy molecule that stores the potential energy originally derived from the electrons donated by NADH and FADH2, which can then be used by the cell to do work.