Question

Briefly describe the process by which the body strips electrons from food molecules (use a polysaccharide made up of glucose monomers as an example) and uses them to power the electron transport chain.

Answer 1

The process by which electrons present in food molecule like glucose are used for the formation of ATP in the presence of oxygen is called as oxidative phosphorylation. The overall process of formation of ATP by oxidation of molecule like glucose is called as respiration and if it occurs in the presence of oxygen, it is called as aerobic respiration.

The process begins with the breakdown of one molecule of glucose into two molecules of pyruvic acid. This is called as glycolysis and occurs in cytoplasm.

The second process is the oxidation of pyruvate into acetyl coenzyme a along with the release of carbon dioxide. This process occurs with the help of pyruvate dehydrogenase enzyme complex and occurs in mitochondrial matrix.

The third process is the oxidation of acetyl coenzyme a into carbon dioxide and water in mitochondrial matrix. This is called as citric acid cycle or tricarboxylic acid cycle.

High energy electron carriers, NADH and FADH2 generated during glycolysis, pyruvate oxidation and citric acid cycle enter electron transport chain taking place in inner mitochondrial membrane. They donate their electrons to the electron carriers located in the inner mitochondrial membrane itself. This results in the passing of electrons from one electron carrier to the other. Electron carriers are arranged in increasing order of their electrode potential. Ultimately the electrons are accepted by oxygen to form water which is the byproduct of cellular respiration.

When electrons are passed on from one electron carrier to the other, protons are also pumped from mitochondrial matrix to intermembrane space. This results in an acidic pH of the intermembrane space. This results in the formation of a proton gradient across inner mitochondrial membrane. The protons are diffused back into the mitochondrial matrix by ATP synthase enzyme. This results in the spinning of this enzyme and formation of ATP by phosphorylation of ADP. This is called as oxidative phosphorylation. This is also called as chemiosmosis because the process of oxidative phosphorylation uses energy stored in electrochemical gradient of protons for the synthesis of ATP.

So the electrons present in glucose were passed on to the higher energy electron carriers, NADH and FADH₂ and then to oxygen to form water. In this process, Proton gradient was generated which was utilised for the formation of ATP.

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