Question

Explain how the electrons, which have reduced coenzymes, are delivered to the electron transport chain and how they are transported to oxygen.

In what form is the energy stored as, when the electrons are passed through the chain.

Explain how the energy generated by the electron transport chain
is coupled to the formation of ATP by oxidative phosphorylation.

Answer 1

• Electron transport chain is responsible for the production of ATP via chemiosmosis. This is the last step of aerobic respiration.It takes place across the inner mitochondrial membrane is also known as oxidative phosphorylation.A proton gradient is created across the membrane which releases energy and is then used to produce energy.Electrons are delivered into the electron transport chain through reduced coenzymes NADH and FADH2 .NADH and FADH2 comes from other processes of cellular respiration.By releasing the electrons they turn into NAD+ and FAD.Electrons are transported to oxygen through electron carriers.Electron carriers in ETS are NADH ,ubiquinone,cytochrome b-c1 complex, cytochrome c and cytochrome c oxidase.Electrons move across the carriers from a higher energy level to a lower energy level.There re four complexes in this.Complex I,Complex II,Complex III and Complex IV.NADH passes electrons to ubiquinone in complex I.From complex II ,FADH2 releases electrons to ubiquinone.In complex III, ubiquinone transfers electrons to cytochrome b that transfers electrons to cytochrome c1.Then to cytochrome c.In complex IV ,electrons are transferred to cytochrome c oxidase and finally to oxygen.
• When electron carriers transports electron ,their energy level decreases and releases that energy.In complex I four hydrogen ions are pumped into the intermembrane space from matrix when electrons are released from NADH.Complex III also pumps hydrogen to intermembrane space.This repeats in complex IV.This will accumulate protons in the intermembrane space and by this accumulation of protons,energy is stored temporarily.
• Due to the pumping of protons into the intermembrane space and transfer of electrons ,an electrochemical gradient is created across the inner mitochondrial membrane.The outside of mitochondrial membrane is positive due to the presence of protons and inside is negative due to the lose of protons.This creates a proton gradient.The electron transport chain and oxidative phosphorylation is coupled by this proton gradient.Since there is high concentration of protons outside the inner mitochondrial membrane,protons are pushed into the matrix.But protons can move into the matrix from inner membrane space only through ATP synthase.This movement of protons down their electrochemical gradient cause ATP synthase to turn around,bind ADP with Pi and produce ATP.