Synthesis of ATP

Synthesis of ATP

ATP can be synthesized in three ways:

  1. 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.

 Oxidative phosphorylation


     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


     3. Photophosphorylation:

  • 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.


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