The amino acids as buffers

Many other amino acids exist as dipolar ions or zwitteriom (which means two ions ). These dipolar structures exist even when the acids dissolve in water, and are responsible for some unusual properties. 

Amino acids are the molecular units from which large macromolecules, known as proteins, are made. 

Proteins have both acidic and basic properties because of their amino (basic) and carboxyl (acidic) groups at the ends of the peptide chain. It is therefore possible for proteins to combine with both acids and bases, enabling them to function as buffers. 

Joining amino acid units by a condensation reaction 

Like ordinary amines, amino acids are proton acceptors, but it is not the lone pair on the nitrogen atom that holds the ion, because in free amino acids at neutral pH the nitrogen atom is already protonated. 

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