Cyclic phosphorylation

• Cyclic phosphorylation involves photosystem 1 only
• in cyclic: light is absorbed by photosystem 1 (located in thylakoid membrane) and passed to the photosystem 1 primary pigment (P700)
• An electron in the primary pigment molecule (chlorophyll molecule) is excited to a higher energy level and is emitted from Chlorophyll molecule in a process known as photoactivation
• excited electron is captured by electron acceptor and transported via a chain of electron carriers known as (ETC) before being passed back to chlorophyll molecule in photosystem 1 (cyclic)
• as electrons pass through ETC, provide energy to transport protons from the stroma to thylakoid lumen via proton pump
• buildup of protons in thylakoid lumen can then be used to drive synthesis of ADP to ATP from ADP and inorganic Pi group by chemiosmosis
• Chemiosmosis is movement of chemicals (protons) down the concentration gradient, the energy released can be used by ATP synthase to synthesize ATP
• ATP is then passed to the light-independent reactions
• Cyclic phosphorylation diagram