Electron Transport System (ETS) and Oxidative Phosphorylation

 

Electron Transport System (ETS) and Oxidative Phosphorylation 

The  objective of this respiratory process is  - To release the energy  that is stored in NADH2 and FADH2. The energy is released when NADH2 and FADH2  are oxidised through the electron transport system. During this process,  electrons are passed to oxygen and led the  formation of H2O. 

The metabolic pathway through which the electron passes from one  electron carrier to another electron carries is called the electron transport system.

This electron transport system takes place in the inner mitochondrial membrane. 

Electrons  that are formed from NADH  during the citric acid cycle are oxidised by complex - first  NADH dehydrogenase and electrons are then transferred to ubiquinone located within the inner membrane. 

Ubiquinone also receive electron from complex  Second FADH2 that is generated during the conversation   of succinic acid into malic acid in the citric acid cycle. The reduced ubiquinone is now termed  ubiquinol.

Ubiquinol get oxidised when it transfer the  electrons to cytochrome c  through the complex third cytochrome bc1.

Cytochrome c is a small protein  present at  the outer surface of the inner membrane of mitochondria.

Ctyochrome also is mobile carrier  and transfer of electrons between cytochrome bc1 and complex fourth ctyochrome  c oxidase. It contain  cytochromes a and a3 , and two copper centres. 

When the electrons pass from one electron  carrier to another electron carrier through  complex first to fourth  in the electron transport chain, they are  intermingled with  the complex fifth ATP synthase for the production of ATP from ADP and inorganic phosphate. 

👌👌Remember The number of ATP molecules synthesised depends on the nature of the electron donor. Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, whereas one molecule of FADH2 produces 2 molecules of ATP.

Although the aerobic process of respiration takes place only in the presence of oxygen, the role of oxygen is limited to the terminal stage of the process. Yet, the presence of oxygen is vital, since it drives the whole process by removing hydrogen from the system. Oxygen acts as the final hydrogen acceptor. 

During respiration, Phosphorylation derive energy by the oxidation-reduction therefore it is called  oxidative phosphorylation. 

As chemiosmotic hypothesis  explain that the energy released during the electron transport system is used  in formation  of ATP with the help of complex fifth  ATP synthase. This complex consists of two major components, F1 and F0. The F1  is a peripheral membrane protein complex and contains the site for synthesis of ATP from ADP and inorganic phosphate Whereas F0 is an integral  protein complex that forms the channel through which protons are moved in to the inner membrane. 

The transport  of protons through the channel is associated with  to the catalytic site of the F1 for the production of ATP. For each ATP produced, 4H+ or  proton are transported    through channel of  F0  to F1 for formation of ATP.

Oxidative phosphorylation

Oxidative phosphorylation is the terminal oxidation of aerobic respiration. It is the process in which ATP is formed with the help of electron transferred from the electron transport chain.

F1particle is the site of oxidative phosphorylation. It contains ATP synthase enzyme.

When the concentration of proton is higher at F0 than in F1 particle, ATP synthase became active for ATP synthesis.

The energy from proton gradient is used to attach the phosphate radicle and ADP by high energy bond produce ATP.