Sunday, February 6, 2011

How cells convert Energy? (OR) How ATP is obtained? (OR) Describe Phosphorylation and Chemiosmossis


Within their cells, animals make ATP to carry out normal activities of the body. The process of formation of ATP is known as phosphorylation. There are number of processes through which ATP can be obtained. Two of these processes are common namely substrate level phosphorylation and chemiosmossis.

(1)        Substrate level phosphorylation:
The generation of ATP by coupling strongly exergonic reaction with ATP synthesis from ADP and phosphate is called substrate level phosphorylation. It appeared very early in the history of organisms because organisms initial use of carbohydrates as an energy source is accomplished by substrate level phosphorylation. The mechanism for substrate level phosphorylation is present in most living animal cells. Substrate level phosphorylation is one of the most fundamental of all ATP generating reactions. ATP formation from ADP and phosphate requires the input of energy of 7.3 K. Cal:

(2)        Chemiosmosis:
There is still other method of generating ATP that is more efficient and effective and is called chemiosmosis and it takes place in the mitochondrion. In the mitochondrion trans membrane channels are present in the mitochondrial membranes that can pump protons. These proton pumps use flow of electrons to induce a shape change in the protein, which in turn, causes protons to move out of the inner compartment of a mitochondrion. As the proton (H+) concentration in the outer compartment of mitochondrion becomes greater than that of the inside compartment, other protons are driven across the membrane by electrical – chemical proton gradient. As protons move down this gradient between outer and inner mitochondrial compartments, they induce the formation of ATP from ADP, phosphate, and the enzyme ATP synthetase.
The electrons that derive the electron transport system involved in chemiosmosis are obtained form chemical bonds of food molecules in all organisms and from photosynthesis in plants. This electron stripping process is called cellular respiration or aerobic respiration because free oxygen is needed. Basically aerobic respiration is the oxidation of food molecules to obtain energy.

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