Question

Describe the purpose of the eTC and how it works using both NADH and FADH2 as examples, and

how it maintains the proton gradient. Then explain how ATP synthase utilizes the gradient in order to

make ATP, and approximately how many ATP are produced by ATP synthase per glucose molecule.

Answer 1

Electron transport chain is the last process of cellular respiration. In this process, electrons are transported from one electron Carriers to the other.

It takes place in the inner mitochondrial membrane where all the electron Carriers are embedded and arranged according to their redox potential. The electron carrier with lower redox potential comes first and the one with higher redox potential comes in the end. The one with lower redox potential has lower affinity for electrons and transfer the electrons to the one with higher redox potential which has higher affinity for electrons.

The electron donors are high energy electron Carriers, NADH and FADH₂ which are synthesized in glycolysis, pyruvate oxidation and tricarboxylic acid cycle. They donate their electrons to the first Complex of electron transport chain which then passes the electrons to the subsequent electron carriers.

When electrons are passed on from one electron carrier to the other, each electron carrier pumps protons from mitochondrial Matrix to the intermembrane space. It creates a high Proton gradient or low pH in the intermembrane space. The protons are pumped back into the mitochondrial matrix by ATP synthase enzyme. This creates a Proton gradient across the inner mitochondrial membrane. This Proton gradient is responsible for the spinning of ATP synthesis enzyme which than drives ATP synthesis by phosphorylating ADP with inorganic phosphate.

The process of formation of ATP by ATP synthase enzyme in the presence of oxygen using energy derived from Proton gradient is called as oxidative phosphorylation.

In aerobic respiration, one molecule of glucose is oxidised to carbon dioxide and water to produce molecules of ATP.

Below is the balance sheet for respiration -

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