Synthesis of ATP
ATP can be synthesized in three ways:
- Oxidative phosphorylation :
- The process of synthesis of ATP via electron transport chain is known as oxidative phosphorylation.
- In electron transport chain, electron are transferred through a series of electron acceptors by redox reactions.
- The electrons carried by a molecule of NADH+H+ release 3 ATP whereas the electron carried by a molecule of FADH2 release 2 ATP through electron transport chain.
- The ATP is synthesized by the ATPase complex.
2. Substrate level phosphorylation :
- When energy is trapped directly from the substrate without the help of complicated electron transport chain, it is called substrate level phosphorylation.
Substrate level phosphorylation
- There are two types of photophorylation
a. Cylic Photophosphorylation:
- In Cylic Photophosphorylation, the molecule of baacterila chlorophyll absorb the quantum of light.
- The energy of light raises the molecule to an excited state.
- The excited bacterial chlorophyll gives electron to ferredoxin and then to ubiquinone.
- The electron successively passes to Cytochrome b and to Cytochrome f and finally back to the positively charged bacteriochlorophyll.
- The energy released between Cyt b and Cyt f is used for photophosphorylation.
b. Non-Cylic Photophosphorylation:
- In plants, algae and cyanobacteria, non cyclic photophosphorylation takesplace.
- When amolecule in pigment system II absorbs light, the molecule is excited and releases electrons.
- The released electrons passes to plastoquinone to Cyt b and then to Cyt f and finally to pigment system I.
- Photophosphorylation occurs generating ATP from ADP and iP between Cyt b and Cyt f.
- The photo-system I release that electron when it absorbs light.
- The electron is then transferred to ferredoxin to flavoprotein and finally to NADP+.
- Photophosphorylation occurs when electrons passes to ferredoxin.
- The electron loss by pigment system I is replaced from photolysis of water.