Explain the reactions taking place in mitochondrial inner membrane.

Explanation

In mitochondria, the inner membrane is folded in the form of finger projection towards the matrix called Cristae. In Cristae many oxisomes (`F_1` particles) are present which have electron transport carries the present. According to Peter Mitchell's Chemiosmotic theory this electron transport is coupled to ATP synthesis. Electron and hydrogen (proton) transport takes place across four multiprotein complexes (I - IV). They are
1. Complex - I (NADH dehydrogenase)
It contains a flavorprotein (FMN) and associated with non-heme iron Sulphur protein (Fe - S). This complex is responsible for passing electrons and protons from mitochondrial NADH (Internal) to Ubiquinone (UQ).
`NADH + H^+ + UQ In plants, an additional NADH dehydrogenase (External) complex is present on the outer surface of inner membrane of mitochondria which can oxidise cytosolic `NADH + H^(+)`.
Ubiquinone (UQ) or Coenzyme Quiuone (Co Q) is a small, lipid soluble electron, proton carrier located within the inner membrane of mitochondria.
2. Complex - II (Succinic dehydrogenase)
It contains FAD flavoprotein is associated with non-heme iron Sulphur (Fe - S) protein. This complex receives electrons and protons from succinate in Krebs cycle and is converted into fumarate and passes to ubiquinone.
Succinate `+ UQ rarr Fumarate + UQH_2`
3. Complex-III (Cytochrome bc 1 complex)
This complex oxidises reduced ubiquinone (ubiquinol) and transfers the electrons through Cytochrome `bc_1` Complex (Iron Sulphur centre bc 1 complex) to cytochrome c. Cytochrome c is a small protein attached to the outer surface of inner membrane and act as a mobile carrier to transfer electrons between complex III to complex IV.
`UQH_2 + 2Cyt c_("oxidised") 4. Complex IV (Cytochrome c oxidase)
This complex contains two copper centres (A and B) and cytochromes a and `a_3`. Complex IV is the terminal oxidase and brings about the reduction of `1//2 O_2` to `H_2O`. Two protons are needed to form a molecule of `H_2O` (terminal oxidation).
`2Cyt c_("oxidised") + 2H^(+) + 1//2 O_(2)2Cyt c_("reduced") + H_2O`
The transfer of electrons from reduced coenzyme NADH to oxygen via complexes I to IV is coupled to the synthesis of ATP from ADP and inorganic phosphate (Pi) which is called Oxidative phosphorylation. The `F_0F_1 - ATP` synthase (also called complex V) consists of membrane . `F_0` is present in inner membrane and acts as a channel through which protons come into matrix.