Proteins are essential contituents of all cells,both plants and animals.the nucleus and protoplasm of every cell is composed of protien.protien is absolutely essential in the human diet.because it is the only nutrient which supplies nitrogen and this is vital for cell formation,and there fore growth.the body is uable to synthesis nitrigen from the plentiful supplies which abound in nature.in the air and in the soil,for instance so it must be provided with nitrogen in suitable organic form. Protein are macromolecules of higher mass weight(relative formula mass or molecular mass).typically between several thousands and several million,contain of chains of amino acids .they are polymers.there are 20 different amino acids which are commonly found in naturally occurring proteins. The potential variety of proteins is unlimited because the sequence of amino acids in genetically controlled by the DNA of the cell in which it is made.
In order to understand the functions of proteins at a molecular level ,it is often necessary to determine the three dimensional structure of the proteins.This is the topic of the scientific field of structural biology, that employs techniques such as X-ray crystallography or NMR spectroscopy to determine the structure of proteins.
Proteins exhibit four levels of organization. Primary structure, Secondary structure, Tertiary structure, Quaternary structure.
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