Photophosphorylation in the context of "Adenosine diphosphate"

Chemiosmosis is the movement of ions across a semipermeable membrane through an integral membrane protein, down their electrochemical gradient. An important example is the formation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H) through ATP synthase during cellular respiration or photophosphorylation.

Hydrogen ions, or protons, will diffuse from a region of high proton concentration to a region of lower proton concentration, and an electrochemical concentration gradient of protons across a membrane can be harnessed to make ATP. This process is related to osmosis, the movement of water across a selective membrane, which is why it is called "chemiosmosis".

Otto Kandler (23 October 1920 in Deggendorf – 29 August 2017 in Munich, Bavaria) was a German botanist and microbiologist. Until his retirement in 1986 he was professor of botany at the Ludwig Maximilian University of Munich.

His most important research topics were photosynthesis, plant carbohydrate metabolism, analysis of the structure of bacterial cell walls (murein/peptidoglycan), the systematics of Lactobacillus, and the chemotaxonomy of plants and microorganisms.He presented the first experimental evidence for the existence of photophosphorylation in vivo. His discovery of the basic differences between the cell walls of bacteria and archaea (up to 1990 called "archaebacteria") convinced him that archaea represent an autonomous group of organisms distinct from bacteria. This was the basis for his cooperation with Carl Woese and made him the founder of research on the Archaea in Germany. In 1990, together with Woese, he proposed the three domains of life: Bacteria, Archaea, Eucarya. Finally, on the basis of his lifelong interest in the early evolution and diversification of life on this planet, Kandler presented his pre-cell theory, suggesting that the three domains of life did not emerge from an ancestral cell, e.g. the last universal common ancestor (LUCA), but from a population of pre-cells.

Light-dependent reactions are the chemical reactions involved in photosynthesis induced by light; all light-dependent reactions occur in thylakoids. There are two light-dependent reactions: the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI).

PSII absorbs a photon to produce a so-called high energy electron which transfers via an electron transport chain to cytochrome b₆f and then to PSI. The then-reduced PSI, absorbs another photon producing a more highly reducing electron, which converts NADP to NADPH. In oxygenic photosynthesis, the first electron donor is water, creating oxygen (O₂) as a by-product. In anoxygenic photosynthesis, various electron donors are used.Cytochrome b₆f and ATP synthase work together to produce ATP (photophosphorylation) in two distinct ways. In non-cyclic photophosphorylation, cytochrome b₆f uses electrons from PSII and energy from PSI to pump protons from the cytoplasm (or stroma in chloroplasts), to the lumen of the thylakoid. The resulting proton gradient across the thylakoid membrane creates a proton-motive force, used by ATP synthase to form ATP. In cyclic photophosphorylation, cytochrome b₆f uses electrons and energy from PSI to create more ATP and to stop the production of NADPH. Cyclic phosphorylation is important to create ATP and maintain NADPH in the right proportion for the light-independent reactions.