ELECTRON TRANSPORT CHAIN

The collection of electron carrier molecules embedded in the inner membrane Of the mitochondrion is called electron transport chain. I he folding of the inner membrane forms cristae. These cristae contains electron carrier in the form ()I prosthetic groups. Prosthetic groups are Lightly bound to molecules of proteins. The prosthetic groups are non protein components. These prosthetic groups alternate between reduced and oxidized states during electron transport chain. They accept and donate electrons. There are following steps of electron transport chain:

I. NADH to FMN: Electrons are removed from food during glycolysis and the Krebs cycle. These electrons form NADH,. NADI 4, transfers the electrons to flavoproteil• Flavoprotein is the first molecule of electron transport chain. The flavoprotein has a prosthetic group called mononucleotide (WN).

  1. FMN to Fe.S: The FMN passes electrons to an iron-sulfur protein (Fe-S). It is one of a family of proteins in which both iron and sulfur tightly bound. It is a redox reaction. The FMN returns to its oxidized form.
  2. Fe.S to Ubiquinone (Q): The iron protein then passes the electrons to a compound ubiquinone. This electron carrier is-the only member of the electron transport chain that is not a protein. A molecule of ATP is synthesized during this transfer.
  3. Ubiquinone to Cytochromes: Most of the remaining electron carriers between 0 and oxygen are proteins called cytochromes.Their prosthetic group is called haem group. Haem group is an organic ring. It is surrounded by a single iron atom. The electron chain has several types of cytochromes. Each group has a different protein with a haem group. These are:
    • Cytochrome b
    • Cytochrorne
    • Cytochrome c
    • Cytochrome a
    • Cytochrome a3

    The last Cytochrome passes its electrons to oxygen It also picks up a pair of hydrogen ions from aqueous medium to form water. Two molecules of ATP are produced during this transfer of electron through the cytochronies.

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FADH2 an alternate source of electron

Another source of electrons for the transport chain is FADI12. It is produced during Krebs cycle. FADH, adds its electrons to transport chain at a lower energy level than that of NADH. Therefore, the electron transport chain provides about one third less energy than FADH,. The electron transport chain makes no ATP directly. Its function is to pass electrons from food to oxygen. It breaks a large free energy drop into a series of smaller steps that release energy in manageable amounts. Mitochondria synthesize ATP during a mechanism called chemiosmosis.

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