Light is caught by two photosystems, water is split, and electrons run down a chain in a zig-zag called the Z scheme. Here you see how that run builds a proton gradient, and how the gradient makes ATP while NADPH is formed.
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Created by StemPy LabThe light reactions use light, water, ADP and NADP+ to make ATP and NADPH and to release oxygen. Two photosystems, PS II and PS I, do the work. Each has an antenna of hundreds of pigment molecules that passes energy to one chlorophyll a at the reaction centre: P680 in PS II and P700 in PS I. PS II also splits water.
In non-cyclic photophosphorylation electrons go from water through PS II, the electron transport chain (plastoquinone, cytochrome b6-f, plastocyanin) and PS I to NADP+, in a Z shape. It gives ATP, NADPH and oxygen. In cyclic photophosphorylation only PS I works, and the electron returns to PS I. It gives ATP only.
ATP is made by chemiosmosis. Splitting of water, the carrying of protons by plastoquinone and the use of protons by NADP reductase make the lumen rich in protons and the stroma poor. The protons flow back through the CF0 channel of ATP synthase. This changes the shape of CF1 on the stroma side, which makes ATP.
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