Electron Transport System

AEROBIOSIS – Electron Transport System

 

•ELECTRON TRANSPORT SYSTEM

– also known as cytochrome or respiratory chain.

–it is a functional unit consisting of coenzymes in which H+ and electrons are transferred from one coenzyme to another and finally accepted oxygen

•The electron transport chain has the following characteristics:

1.At certain stage when the electron is transferred from one coenzyme to another, enough energy is given out and is used to form ATP from ADP and phosphate.

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2.The coenzymes NADH + H+ and FADH2 at the beginning of the chain come from dehydrogenation in the course of the break down of glucose.

3.One NADH + H+ can form 3 ATP whereas one FADH2 can form 2 ATP

 

•ATP is produced by a process called CHEMIOSMOSIS.

a)Five electron carrier proteins also called electron transport chain are embedded in the inner mitochondrial membrane.

b)Initially, NADH + H+ pass the electrons to NADH dehydrogenase, then to a carrier called ubiquinone, then to a protein-cytochrome complex called bc1 complex, then to another carrier called cytochrome c and finally to a cytochrome oxidase complex.

 

•ATP is produced by a process called CHEMIOSMOSIS.

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c)The cytochrome oxidase needs oxygen to function in which it gets the H+ from the inner matrix to form water, i.e.

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O2  +  4H+  +  4 e-                               2H2O

d)  FADH2 is always found in the inner side of the membrane and passes its electrons to ubiquinone.

•ATP is produced by a process called CHEMIOSMOSIS.

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e)NADH dehydrogenase, bc1 complex and cytochrome also function as proton pumps, pumping H+ from the matrix to the inter-membrane space.  Thus, more H+ are found in the inter-membrane space than the matrix.

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f)This causes chemiosmosis.  The H+ re-enter the matrix through a channel protein functioning also as an enzyme called ATP synthetase.  ATP is produced from ADP and phosphate through this diffusion process. It is also an oxidative phosphorylation.

•Hence from one pyruvate, four NADH + H+, one FADH2 and one GTP are produced.

•The total ATP formed is calculated as follows :

a)4 NADH + H+ can produce    4 x 3ATP = 12 ATP

b)1 FADH2 can produce            1 x 2ATP =   2 ATP

c)1 GTP can produce                1 x 1ATP =   1 ATP

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d)Therefore total ATP produced per pyruvate = 15

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e)Total ATP produced per glucose is equal to 30 and together with 6 ATP produced in glycolysis, a total of 36 ATP can be produced