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An Account of Proteins and their Structure

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An Account of Proteins and their Structure It is difficult to describe in a simple sentence the role of proteins. Let's say: When there is something to do, it is a protein that does it. Some examples of proteins * Antibodies: they recognize molecules of invading organisms. * Receptors: part of the cell membrane, they recognize other proteins, or chemicals, and inform the cell. * Enzymes: assemble or digest. The role (or function) of a protein depends on its shape, and chemical formula. Proteins play a number of vital roles in all organisms. Unlike carbohydrates and lipids they always contain nitrogen as well as carbon, hydrogen and oxygen. Sulphur is often present. The building blocks of the proteins are amino acids. Proteins are made of a long chain of amino acids, sometimes modified by the addition of sugars and phosphates. Amino acids unite to form proteins in much the same manner the monosaccharides combine to form polysaccharides, and fatty acids and glycerol combine to form fats and oils. This happens when two amino acids reacts. ...read more.


Beta - pleated sheets: the amino acids adopt the conformation of a sheet of paper and the structure is stabilized by hydrogen bonds between amino acids in different polypeptide strands. Note that some of the strands are parallel and some are antiparallel. Other parts of the structure are not highly stable, and adopt a random coil formation. The tertiary structure refers to the way random coils, alpha helixes and beta pleated sheets fold in respect to each other, i.e. it refers to the protein as a whole. Amino acids which are very distant in the primary structure might be close in the tertiary one because of the folding of the chain. They are still held by hydrogen bonds like the primary and secondary but in this stage sulphur bridges and ionic bonds are involved. The quaternary structure is only present when a protein consists of two or more polypeptides. It refers to the way these polypeptides are arranged to form the biologically active protein. A good example is the quaternary structure of haemoglobin, made up of two alpha and two beta polypeptide chains. ...read more.


Among the many other classes of globular proteins, special mention should be made of antibodies. Each of us can make hundreds of thousand of different antibodies, which bind to particular disease-causing agents and toxins. Fibrous proteins are insoluble and consist of long, parallel polypeptide chains cross linked at many points along their life. They are essential for many structures in the body. E.g. keratin is found in the skin and in hairs, feathers, nails, hooves and horns. Collagen is another fibrous protein. It is the most abundant protein in vertebrates, making up a third of their total protein mass. The human body is mainly held together by collagen as it is found in bones, cartilage, tendons, ligaments, connective tissue and skin. Collagen fibres have a tensile strength greater than steel which makes it very strong. Careful analysis of collagen had shown that they consist of three polypeptide chains coiled round each other in a triple helix. The resulting structure is like a plaited rope and has great strength. In conclusion proteins are probably the most important class of biochemical molecules, although of course lipids and carbohydrates are also essential for life. Proteins are the basis for the major structural components of animal and human tissue. ...read more.

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