Write a short note on cyclic photophosphorylation
In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation.
Only two sources of energy are available to living organisms: sunlight and reduction-oxidation (redox) reactions. All organisms produce ATP, which is the universal energy currency of life. Commonly in photosynthesis this involves photolysis, or photodissociation, of water and a continuous unidirectional flow of electrons from water to PS|| .
In photophosphorylation, light energy is used to create a high-energy electron donor and a lower-energy electron acceptor. Electrons then move spontaneously from donor to acceptor through an electron transport chain.
- Photophosphorylation may be either a cyclicprocess or a non-cyclic process
Cyclic Photophosphorylation
- Cyclic photophosphorylation involves the use of onlyone photosystem (PS I) and does not involve the reduction of NADP+
- When light is absorbed by Photosystem I, the excited electron may enter into an electron transport chain to produce ATP
- Following this, the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic)
- As the electron returns to the photosystem, NADP+is not reduced and water is not needed to replenish the electron supply
Non-Cyclic Photophosphorylation
- Non-cyclic photophosphorylation involves twophotosystems (PS I and PS II) and does involve the reduction of NADP+
- When light is absorbed by Photosystem II, the excited electrons enter into an electron transport chain to produce ATP
- Concurrently, photoactivation of Photosystem I results in the release of electrons which reduce NADP+ (forms NADPH)
- The photolysis of water releases electrons which replace those lost by Photosystem II (PS I electrons replaced by PS II)
Hope it helps
In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation.
Only two sources of energy are available to living organisms: sunlight and reduction-oxidation (redox) reactions. All organisms produce ATP, which is the universal energy currency of life. Commonly in photosynthesis this involves photolysis, or photodissociation, of water and a continuous unidirectional flow of electrons from water to PS|| .
In photophosphorylation, light energy is used to create a high-energy electron donor and a lower-energy electron acceptor. Electrons then move spontaneously from donor to acceptor through an electron transport chain.
- Photophosphorylation may be either a cyclicprocess or a non-cyclic process
Cyclic Photophosphorylation
- Cyclic photophosphorylation involves the use of onlyone photosystem (PS I) and does not involve the reduction of NADP+
- When light is absorbed by Photosystem I, the excited electron may enter into an electron transport chain to produce ATP
- Following this, the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic)
- As the electron returns to the photosystem, NADP+is not reduced and water is not needed to replenish the electron supply
Non-Cyclic Photophosphorylation
- Non-cyclic photophosphorylation involves twophotosystems (PS I and PS II) and does involve the reduction of NADP+
- When light is absorbed by Photosystem II, the excited electrons enter into an electron transport chain to produce ATP
- Concurrently, photoactivation of Photosystem I results in the release of electrons which reduce NADP+ (forms NADPH)
- The photolysis of water releases electrons which replace those lost by Photosystem II (PS I electrons replaced by PS II)
Hope it helps
