Proteins 



Proteins are essential constituents of all living cells. In fact they 

 appear to be involved in practically all the structures and functions 

 of all cells. Owing to the great molecular size and exceedingly complex 

 structure of proteins, it is deemed advisable to consider first the amino 

 acids. These compounds are combined to form the larger structures, 

 peptides and proteins. 



AMINO ACIDS 



Amino acids are organic compounds having at least one amino or 

 imino group and one carboxyl group. Other functional groups may 

 be present. The chemical properties of these compounds are those of 

 the amino, carboxyl, and other functional groups with certain special 

 interactions due to the presence of these different structures in a single 

 molecule. Certain of these intramolecular interactions are chiefly 

 responsible for the biological importance of the amino acids. 



Occurrence 



The almost limitless number of theoretically possible amino acids 

 fortunately does not occur naturally. The natural examples are found 

 both in free and in combined form. Most have the amino group at- 

 tached to the carbon atom alpha to the carboxyl group. Thus a 

 majority fit the general formula 



R— GHGOQ- 



NHJ 



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