Wednesday, August 08, 2018

Physical properties of proteins

Nearly half of the dry weight of a typical animal cell is protein. Structural components of the cell, antibodies, and many of the hormones are proteins but as much as 90% of cellular proteins are the enzymes upon which fundamental cellular function depends. They may be as many as 1000 different enzymes in a single cell.

The protein molecule is a polymer of amino acids joined in peptide linkages. Although the molecular weight is usually high, there is a vast range in both structure and complexity of protein molecules. Hemoglobin for example, has a molecular weight of about 64,500; myosin, a muscle protein is estimated to have a molecular weight of about 489,000.

It is not uncommon for peptide structures of fairly low molecular weight (less than 10,000 and containing less than 100 amino acids) to be designated polypeptides rather than proteins. On the average, about 20 different amino acids occur in most proteins, the amino acids present, their position in the molecule, and the spatial arrangement of the molecule all determine the proteins and characteristics of the proteins. In turn the function of a protein depends, in large measure, on its structure.

Other physical properties of proteins
*Dissociation
*Denaturation: denaturation refers to the changes in the properties of a protein. In other words, it is the loss of biologic activity. In many instances the process of denaturation is followed by coagulation— a process where denatured protein molecules tend to form largeaggregates and to precipitate from solution.
*Optical Activity
*Solubility, Hydration and Swelling Power
*Foam Formation and Foam Stabilization
*Emulsifying Effect
*Colour and taste: Proteins are colorless and usually tasteless. These are homogeneous and crystalline
*Shape and size: the proteins range in shape from simple crystalloid spherical structuresto long fibrillar structures.
Physical properties of proteins

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