Cyclic and non-cyclic photo-phosphorylation
- The process in which ATP is synthesised by cells in mitochondria and chloroplasts is named phosphorylation.
- Photophosphorylation is the synthesis of ATP from ADP and inorganic phosphate in the presence of light.
- When the two photosystems, first PS II and then the PS I, connected through an electron transport chain work in a series, the process is called non-cyclic photo-phosphorylation.
- When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs due to cyclic flow of electrons in the stroma lamellae.
- The stroma lamellae membranes lack PS II as well as NADP reductase enzyme, hence the excited electron does not pass on to NADP+ but is cycled back to the PS I complex through the electron transport chain.
- The cyclic flow results only in the synthesis of ATP, but not of NADPH + H+.
Fig. Cyclic phosphorylation