Chemistry - Proteins
Much of life revolves around the action of proteins.
Proteins are found in all parts of the body. The main constituents of all
living cells are water and proteins, with proteins accounting for
two-thirds of the dry mass.
Protein is usually the most expensive type of nutrient and hence the most
likely to be lacking in the diets of poorer nations. There is a close
connection between the standard of living and the proportion of protein to
carbohydrate in the diet.
The general functions of proteins are:
* the growth (via the building of new tissue);
* maintenance and repair of tissue,
* and for the control of life processes.
Proteins take an active part in chemical reactions in cells and also form
part of the cell structure. They help in the digestion of food, in carrying
oxygen in the blood, and in clotting blood. Proteins in the form of enzymes
 speed up almost every essential reaction in our bodies. Our immune
system uses proteins as antibodies.
Protein molecules are generally very large. The molecular formula of
lactoglobulin, a protein found in milk is:
Proteins are condensation polymers of amino acids. 
Amino acids and proteins are the main nitrogen-containing compounds in
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