Question

Explain electron transport system

Answer 1

The metabolic pathway of electron transport is called as electron transport system or ETS.
Glycolysis and Krebs cycle result in the formation of reduced coenzymes such as 10 molecules of NADH +H+ ions and 2 molecules of FADH2 and 4 molecules of ATP. These reduced coenzymes need to be oxidized to release energy stored in them. This is possible by the transport of electrons and protons from these coenzymes to oxygen through electron carriers present in the inner mitochondrial membrane. This metabolic pathway of electron transport is called as electron transport system or ETS.

ETS comprises of several energy carriers which include NADH dehydrogenase complex (Complex I), Ubiquinone (Complex Q), Succinate dehydrogenase complex (complex II), Cytochrome bc1 complex (Complex III), Cytochrome c, Cytochrome c oxidase (Complex IV)

Steps in ETS:
*Electrons are transferred from NADH+H+ to Ubiquinone through complex I and protons are moved from mitochondrial matrix to intermembrane space.
*Electrons from FADH2 are transferred to Ubiquinone through complex II and protons are moved from mitochondrial matrix to intermembrane space.
*Ubiquinone transfers the electrons to complex III.
*Complex III transfers electrons to complex IV through Cytochrome c. Some protons are moved from mitochondrial matrix to intermembrane space.
*Complex IV contains Cytochrome a and Cytochrome a3. It transfers the electrons to final acceptor, the oxygen.
*Oxygen combines with 2 H+ ions and reduces to water which drives ETS.
2H+ + 2e- + ½ O2 --------- H2O + Energy

Coupling of ETS with ATP synthesis:
Protons from intermembrane space are pumped into matrix by ATP synthase (Complex V).
Energy derived from proton pumping is utilised in ATP synthesis. When 2 protons are pumped from intermembrane space into matrix, 1 ATP molecule is synthesized.
Oxidation of NADH + H+ results in synthesis of 3 ATP molecules. Oxidation of FADH2 results in synthesis of 2 ATP molecules.