Respiration on the mitochondrion inner membrane

Here is described the energy conversion of food in heterothrophs (respiration).

NADH - a high energy molecule that receives its energy from food in the citric acid cycle gives away proton and high energy electron which spends some of its energy to enable pumping of protons across the membrane. Protons establish a proton gradient which is used to produce another high energy molecule - ATP like water gradient is used in turbines to produce power.