The chemiosmotic hypothesis proposes that ATP synthesis occurs through the proton gradient established by the electron transport chain in mitochondria. The spelling of "chemiosmotic" reflects the Greek origins of the word. The "ch" is pronounced /k/ as in "kite," the "e" is pronounced /i/ as in "ski," the "mio" is pronounced /mi-o/ as in "meow," and the "osmotic" is pronounced /ɑsˈmɑtik/ as in "as-mat-ic." Together, the word is pronounced /kəˌmi:oʊˈsmɑtɪk/ as in "keh-mee-oh-smah-tik."
The chemiosmotic hypothesis is a scientific principle that explains the molecular mechanisms of ATP synthesis within living cells. It proposes that the production of ATP is driven by a proton gradient across a membrane, which serves as an energy source for the synthesis of adenosine triphosphate (ATP). The theory was first proposed by Peter D. Mitchell in the 1960s and has since become widely accepted in the field of bioenergetics.
According to the chemiosmotic hypothesis, the process of ATP synthesis occurs through the action of an enzyme called ATP synthase. This enzyme, located on the inner mitochondrial membrane in eukaryotic cells or the plasma membrane in prokaryotic cells, utilizes the energy from the proton gradient to convert adenosine diphosphate (ADP) and inorganic phosphate (Pi) into ATP.
The chemiosmotic hypothesis suggests that during cellular respiration or photosynthesis, protons (H+) are pumped across a membrane, creating an electrochemical gradient. This gradient results in a difference in proton concentration (pH) and electrical charge (voltage) across the membrane. When the protons flow back through the ATP synthase enzyme, it causes a conformational change that drives the phosphorylation of ADP to ATP.
Overall, the chemiosmotic hypothesis provides a concise explanation for how the energy from electron transfer reactions or light absorption is converted into chemical energy in the form of ATP. This principle is fundamental in understanding the generation of ATP in living organisms and has significant implications for various biological processes, including muscle contractions, active transport, and cellular metabolism.
The word "chemiosmotic" is a combination of the terms "chemio-" and "-osmotic". "Chemio-" refers to chemical processes or reactions, and "-osmotic" relates to osmosis, which is the movement of a solvent through a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.
The term "chemiosmotic hypothesis" was popularized in the 1960s by the British biochemist Peter Mitchell. It describes the mechanism by which cells produce ATP (adenosine triphosphate), the primary source of energy for cellular processes. Mitchell proposed that ATP synthesis occurs through a series of chemical reactions driven by an electrochemical gradient across a membrane. The term "chemiosmotic" emphasizes the coupling of chemical reactions with the movement of ions across a membrane, as mediated by osmotic processes.