Читать книгу Biochemistry For Dummies - John Moore T., Richard Langley H., John T. Moore - Страница 25

Some substances can’t make up their minds about what they are; they can act as either an acid or a base. Chemists classify these substances as amphiprotic or amphoteric substances. For example, the bicarbonate ion can act as either an acid or a base:

 

 

Biochemically important molecules may also exhibit amphiprotic behavior. Amino acids contain both a basic amine group and an acidic carboxyl group. Therefore, they can act as either acids or bases. For example, glycine may undergo the following reactions:

 

 

In fact, amino acids may undergo proton transfer from the carboxyl end to the amine end, forming an overall neutral species that has a positive and negative end. Species such as these are called zwitterions (not to be confused with twitterions — people who tweet until their thumbs fall off):