Electron Transport Chain Process in Plant and Animal Cells :

Electron Transport Chain Process in Plant and Animal Cells!

All living things run on energy. If the organism is a plant or autotrophic microbe, the energy comes from sunlight.

For all other forms of life, energy is extracted from nutrients through the reactions of metabolism-cellular respiration.

(a) Cellular Respiration and the Electron Transport Chain:

Regardless of whether the original form of energy is sunlight or food, it must ultimately be converted to the cellular energy currency of adenosine triphosphate (ATP). For most organisms, this conversion is done by cellular respiration; a series of pathways in which glucose (sugar) is broken down and the energy extracted is converted to ATP.

Cellular respiration pathways include glycolysis, conversion of acetyl-CoA, Kreb’s cycle and electron transport. Electron transport is the most complex and productive pathway of cellular respiration, producing 34 molecules of ATP for every molecule of glucose.

(b) Location of Electron Transport Chain is Located:

Electron transport requires a membrane in order to work. In prokaryotic cells, those of bacteria and bacteria-like Achaeans, electron transport takes place in the cell’s plasma membrane. In eukaryotic cells, the more evolutionarily advanced and complex cells of animals, plants and fungi, electron transport takes place in cellular organelles known as mitochondria-the eukaryotic cell’s tiny power factories.

(c) How Electron Transport Working:

Most of the ATP made in cellular respiration comes from the stepwise release of energy, through a series of oxidation-reduction (redox) reactions between molecules embedded in the plasma membrane (prokaryotes) or mitochondria (eukaryotes).

It is easiest to understand how electron transport works to divide it into three main events:

(i) Oxidation Reduction Reactions:

During glycolysis, synthesis of acetyl-CoA and Kreb’s cycles the electron carriers NAD+ and FADH are reduced to form NAD+ and FADH respectively. These molecules are like little rechargeable batteries, and when NAD+ and FADH are reduced, this means that they accept and carry electrons and hydrogen ions (H+)-potential energy that can be used later in cellular respiration.

In the electron transport chain, these electron carriers are oxidized, transferring their electrons to the carrier molecules embedded in the ETC membrane. The electrons are then passed from one carrier molecule to another in a series of oxidation-reduction reactions, and finally, in aerobic respiration, to the final electron acceptor, oxygen (O2).

(ii) Creation of Hydrogen Ion Gradient:

The energy from each electron being passed down the chain is used to pump a proton (H+) through each carrier molecule, from one side of the membrane to the other. This creates a proton gradient, a type of ion gradient (difference in ion concentration ‘between two sides of a membrane), and gradients are potential energy available for cellular work.

(iii) Phosphorylation of ADP:

The H+ on the side of the membrane in which they are most concentrated will eventually flow back across the membrane, down the electrochemical proton gradient through protein channels called ATP syntheses. As each H+ move back across the membrane, ATP syntheses phosphorylates adenosine di-phosphate (ADP) to make the high energy molecule ATP, which can be used for many different energy-requiring reactions throughout the cell.

The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. The NADH and succinate generated in the citric acid cycle are oxidized, providing energy to power ATP syntheses.