PACKET #32 CHAPTER #10 The Light Reactions Cyclic Electron Flow

Introduction 2/21/ Cyclic electron flow has one function.  Produce ATP During non-cyclic electron flow, insufficient ATP’s are produced.  The deficit/deficieincy in ATP’s is closed via cyclic electron flow.

Introduction II Cyclic electron flow requires the use of  Photosystem  Photosystem I  Mobile electron acceptors  Ferrodoxin  Plastocyanin  Stationary electron acceptor  Cytochrome B6F  Enzyme  ATP synthase

THE PROCESS Cyclic Electron Flow

Cyclic Electron Flow Step by Step I Two electrons, from photosystem I, are inside the mobile electron acceptor ferredoxin.

Cyclic Electron Flow Step by Step II Ferredoxin, instead of taking the electrons to the enzyme ferredoxin NADP+ reductase, takes the electrons back to cytochrome B6F.

Cyclic Electron Flow Step by Step III Once the electrons are in cytochrome B6F, H+ are pumped across the membrane from the stroma into the thylakoid space.

Cyclic Electron Flow Step by Step IV The electrons leave cytochrome B6F into the mobile carrier plastocyanin and are moved to photosystem I where they are once again placed into ferrodoxin.

Cyclic Electron Flow Step by Step V The cycle repeats. The repeating of the cycle allows the formation of the hydrogen gradient which in turn allows for the production of the extra ATP.