photophosphorylation The formation of ATP from ADP and inorganic phosphate using light energy in photosynthesis (compare oxidative phosphorylation). There are two pathways, noncyclic and cyclic photophosphorylation, which occur in the thylakoid membranes of the chloroplasts. In noncyclic photophosphorylation electrons derived from the photolysis of water are raised to higher energy levels in photosystems I and II and pass along an electron transport chain of carrier molecules (see ferredoxin; plastocyanin; plastoquinone) to NADP reductase. This enzyme transfers electrons to NADP+ to make NADPH, which provides reducing power for the light-independent reactions of photosynthesis. In cyclic photophosphorylation the electrons from photosystem I that are raised to a higher energy level are recycled through the electron carrier system back to photosystem I. Both pathways of electron flow cause H+ ions to be pumped by a group of cytochromes, the cytochrome b6–f complex, across the thylakoid membrane. This creates a proton gradient that drives the phosphorylation of ADP to ATP by the enzyme ATP synthetase (see chemiosmotic theory).
More From encyclopedia.com
Oxidative Phosphorylation , Glycolysis and the Krebs cycle both generate the high-energy compound adenosine triphosphate (ATP ) directly, by substrate -level phosphorylation, bu… Atp Synthesis , chemiosmotic theory A theory postulated by the British biochemist Peter Mitchell (1920–92) to explain the formation of ATP in the mitochondrial elect… Cytochrome , Cytochromes are electron-transporting protein pigments concerned with cell respiration that contain an iron-containing molecule called heme, allied t… Photonics , By the 21st century, photonics was on the cusp of unseating electronics as the optimal and revolutionary science underlying cutting-edge telecommunic… Electron Microscopy , The scanning electron microscope (SEM) is an important tool in modern forensic science due to its wide range of applications. SEM allows the rapid an… Scanning Electron Microscope , scanning electron microscope (SEM) A microscope that operates by scanning a finely focused beam of electrons across the specimen. The reflected elect…
About this article
All Sources -
Updated About encyclopedia.com content Print Topic
You Might Also Like