The Mitchell hypothesis is also called as the chemiosmotic hypothesis postulated by a biochemist named Peter Mitchell in 1906's which help him earn the Nobel Prize in Chemistry in 1978. The general statement of the hypothesis can be defined as the production of ATP molecules in the cell is driven by the movement of hydrogen ions across a semipermeable membrane during the cellular respiration.
During the early times, the mechanism of action of ATP (adenosine triphosphate) is not as clear compared today. They only know that it is the main energy source in living systems. He then postulated that most ATP produced by the cells comes from the electrochemical gradient of ions across the membranes of mitochondria.
The movement of ions across the membranes generates potential which is enough to produce ATP from ADP (adenosine diphosphate) and an inorganic phosphate. His hypothesis was then supported by the discovery of the ATP synthase, a membrane that uses the generated potential in the membrane for the conversion from ADP to ATP possible.
Adenosine triphosphate or ATP is the means by which energy is transferred between cells. ATP is produced as a result of several biological processes taking place inside cells that include respiration, photosynthesis, fermentation, etc.
The syntesised ATP is then used as a source of energy by other cells.
When ATP was discovered and the role played by it in cellular metabolism understood, the production of ATP in mitochondria was assumed to be by substrate-level phosphorylation. Peter Dennis Mitchell identified the process of production of ATP by oxidative phosphorylation. He was able to show that there exists a potential difference between two sides of membranes; and that this leads to the movement of charged particles across the membrane. ATP formation is a result of this. This discovery is commonly known as the Mitchell Hypothesis of Chemiosmotic coupling.