Principles of Biochemistry Volume 1 - A. Lehninger 1985

Biomolecules
Water
Amino acids can act as both acids and bases

In an aqueous solution, Amino Acids such as Alanine exist as zwitterions, which function either as acids (proton Donors):

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or as bases (proton acceptors):

Substances with such dual properties are amphoteric (derived from the Greek "amphi" meaning "both") and are frequently referred to as ampholytes (a portmanteau of "amphoteric electrolytes"). A simple monoaminomonocarboxylic $\alpha$-amino acid, such as alanine, is essentially a dibasic acid when in its fully protonated form, meaning protons are attached to both the amino and carboxyl groups. In this state, it possesses two groups capable of releasing two protons upon dissociation, According to the following equation:



Last update: 06/08/2026

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