Cyclic Electron Flow

Linear electron flow produces ATP and NADPH through a series of reactions that occur in the photosystems embedded in the thylakoid membranes of chloroplasts. Cyclic electron flow is the alternative mechanism to linear electron flow that only produces ATP.

Cyclic electron flow is a short circuit that only uses PSI, not PSII. Electrons cycle back from ferredoxin (in the second transport chain) to the cytochrome complex (in the first transport chain). They then travel via the plastocyanin molecule to the P700 chlorophyll in the PSI reaction center complex. By traveling along the 1st transport chain, an electrochemical gradient is produced, which then powers the production of ATP by chemiosmosis. However, there is no NADPH produced because electrons are not transferred to NADP+ via the enzyme NADP+ reductase.

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The Plasma Membrane and the Fluid Mosaic Model

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