Non-Cyclic Photophosphorylation

Non-cyclic photo- phosphorylation,cytochrome b6f uses the energy of electrons from PSII to pump protons from the stoma to the lumen. The proton gradient across the thylakoid membrane creates a proton-motive force, used by ATP synthase to form AT

 Non-cyclic photophosphorylation Process

• Non-cyclic photophosphorylation takes place inside a chloroplast, on or in a thylakoid membrane.
• A photon of light energy strikes the leaf and hits photosystem 2. The energy will pass from one antenna pigment molecule to another until it reaches a reaction center molecule (p680). The light energy will then energize 2 electrons.
• The energized electrons now pass to an electron acceptor this creates an electron "hole" within PS2.
• Water is split inside the thylakoid, providing the electrons to fill the "hole" for photosystem 2. The hydrogen ions, that for the moment are inside the thylakoid, and oxygen which will diffuse out of the chloroplast and the cell.
• From the electron acceptor the electrons pass to plastoquinone (PQ).
• From plastoquinone (PQ) the electrons pass on to a complex of cytochromes.
• As the electrons move from PQ to the cytochrome complex they release enough energy to power the active transport of hydrogen ions from the stroma into the thylakoid space. This generates a large hydrogen ion gradient.
• From the cytochrome complex the electrons pass on to Photosystem 1 to fill an electron "hole" in PS1.
• A photon of light energy strikes the leaf and hits photosystem 1. The energy will pass from one antenna pigment molecule to another until it reaches a reaction center molecule (p700). The light energy will then energize 2 electrons.
• The energized electrons now pass to an electron acceptor this creates the electron "hole" within PS1.
• From the electron acceptor the electrons pass to ferredoxin (Fd).
• From ferredoxin (Fd) the electrons and 2 hydrogen ions are used to reduce NADP+ to NADPH + H+. The NADPH + H+ is going to be utlized in the Calvin Cycle (dark reactions).
• The hydrogen ions that have been pumped into the thylakoid space pass down a concentration gradient through the ATP synthetase complexes. As the ions pass through the synthetase complex their chemiosmotic energy is released.
• The energy released by the hydrogen ions is used to help convert ADP and a phosphate group into ATP. Some of this ATP is going to be utlized in the Calvin Cycle (dark reactions).