PROTEINS FROM SKIN AND BONE TO ENZYMES

So far all the polymer chains we have considered have had backbones consisting of only carbon atoms. But there are some—and they include the most interesting biological polymers— in which 

Strong acids, notably sulphuric acid ( oil of vitriol ), hydrochloric acid ( spirits of salt ), and nitric acid aqua fortis, or strong 

This dissociation of salts into the constituent ions is responsible for the capacity of their solutions in water to conduct 

Amino acids are both acids and bases, and they exist in neutral solutions in the doubly ionized form (called a zwitterion, from the German for a hybrid). So the amino and carboxyl groups are properly written respectively —NHj and —COO . The amino acids, then, have the structure 

But when linked together to form a polypeptide chain, it is only (disregarding, for the moment, the side chains) the chain ends that retain a charge, an amino group at one end, called the N-terminus, and a carboxyl group at the other, the C-terminus. In between are the uncharged peptide groups. The structure looks like this  

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