The Z-Scheme of Electron Transport in Photosynthesis

During photosynthesis, the electron transport sequence from water to NADP⁺ follows a Z-shaped trajectory and is therefore called the Z-scheme.

It begins with water hydrolysis that supplies electrons to the oxidized P680 or PSII reaction center.

After reduction, P680 absorbs photons and transfers an excited electron to PSII's primary electron acceptor–pheophytin.

The reduced pheophytin transfers electrons across a series of acceptor molecules between PSII and PSI, starting from an electron carrier– plastoquinone, followed by a cytochrome b6f complex, and a mobile electron carrier– plastocyanin.

When plastocyanin is reduced, it transfers an electron to the oxidized P700 or PSI reaction center.

The reduced P700 then absorbs light and relays an excited electron to PSI's unique electron acceptor– ferredoxin, followed by ferredoxin-NADP⁺ reductase.

Finally, ferredoxin-NADP⁺ reductase utilizes the electrons to convert NADP⁺ to NADPH.

Overall, the redox changes during the Z-scheme generate an electrochemical proton gradient that drives ATP synthase to produce ATP.