Chemiosmosis

Chemiosmosis refers to ions’ movement across membrane that is selectively permeable down the electrochemical gradient. Specifically, chemiosmosis relates to ATP generation by hydrogen ions’ movement across the membrane during the process of cellular respiration. Hydrogen ions are the protons that diffuse from the area where there is high concentration of protons to the area where proton concentration is lower.

The concept of electrochemical concentration gradient was proposed by Peter Mitchell. He proposed that electrochemical concentration gradient of the protons across the membrane can be harnessed making ATP. The process was linked to osmosis which is water diffusion across the membrane and that is why the process was called chemiosmosis.

The enzyme that is involved in the production of ATP through chemiosmosis is known as the ATP synthase. This enzyme allows for the passage of protons via the membrane. It uses kinetic energy in the phosphate ADP generating ATP. ATP generation through chemiosmosis takes place in mitochondria, chloroplasts, archaea and bacteria.

According to chemiosmotic hypothesis as proposed by Peter Mitchell in 1961, ATP synthesis in the respiring cells results from electrochemical gradient established across the inner mitochondria’s membranes through the use of FADH₂ and NADH energy formed from the breakdown of molecules that are rich in energy such as glucose.

Metabolism of molecules that are rich in energy such as glucose produces acetyl CoA as the energy rich intermediate. Acetyl CoA oxidation in the matrix of mitochondria is combined with reduction of the carrier molecules such as FAD and NAD. Electrons are passed by the carriers to electron transport chain in the inner membrane of the mitochondria which then passes them to the other proteins in the electron transport chain.

Energy that is available in electrons is used in pumping electrons from mitochondrial matrix across the inner membrane of the mitochondria. Energy is stored in form of trans-membrane electrochemical gradient.

Protons then move back across inner membrane via ATP synthase enzyme. Moving back of the proteins in the mitochondria matrix through ATP synthase offers sufficient energy for the ADP combination with the inorganic phosphate forming ATP. Protons and electrons that are pumped lastly in the electron transport chain are used up by oxygen forming water.

Chemiosmosis was considered as a radical proposal when it was suggested for the first time and it was not readily accepted. However, with eventual evidence of the chemiosmotic hypothesis the process was accepted and Peter was award Nobel Prize in Chemistry in 1978 for his scientific contribution.

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Sources

http://www.cliffsnotes.com/sciences/biology/biology/cellular-respiration/chemiosmosis

http://en.wikipedia.org/wiki/Chemiosmosis

http://163.16.28.248/bio/activelearner/07/ch7c6.html