FRANCIS LEROY & LOUIS BEUCLER, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY & LOUIS BEUCLER, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Animation showing the biochemistry of photosynthesis, the process that plants use to convert energy from sunlight into food. Initially, the Sun is seen irradiating a light-harvesting complex (green) in a chloroplast. An enzyme called oxygen-evolving complex (OEC, grey) is shown splitting water molecules into free hydrogen ions (protons, red), oxygen atoms (blue), which combine to form oxygen gas (O2), and electrons (yellow), which are passed to the reaction centre. While this is happening, the light-harvesting complexes pass light energy between each other in a process called resonant energy transfer. Eventually it reaches the reaction centre, called P680, which enters an excited state. The raising of the electrons (yellow) here indicates the rise in energy of the system. The electrons then pass down an electron transport chain (brown slope), where their gradual reduction in energy is used to power other reactions. A molecule in the complex called plastoquinone (red) takes in more of the protons, and the resulting proton gradient across the membrane drives the enzyme ATP synthase (blue and red), which produces ATP (bottom right) from ADP. The electron then enters the second photosystem, called P700. This receives sunlight in the same way as the P680, and again enters an excited state. The electron is raised in energy to a second electron transport chain (top brown slope), which contains the complex ferrodoxin (blue). This is responsible for reducing the molecule NADP+ to NADPH (upper right). ATP and NADPH are both used in the subsequent reaction cycle in which atmospheric carbon dioxide is reduced and incorporated into sugars, the building blocks of plants.
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