Proteins comprise many amino acids joined to each other by peptide links.

This diagram shows a tripeptide, formed from three amino acids. The functional groups R 1, R 2 and R 3 can be the same or different.

Peptide links are often written as –CONH–.

Peptide links can be broken by hydrolysis under acidic or alkaline conditions.

In this example, if one peptide link is hydrolysed an amino acid and a dipeptide form.

If both peptide links are hydrolysed, three amino acids are formed.

Peptides and proteins can be hydrolysed by refluxing with moderately concentrated hydrochloric acid for several hours.

Anti-bumping granules are usually added to the reaction mixture to ensure smooth bubbling.

Peptides and proteins can be hydrolysed by refluxing with moderately concentrated hydrochloric acid for several hours.

The condenser cools and condenses the vapour rising from the flask. This prevents the liquid boiling away.

Aspartame is the methyl ester of the dipeptide Asp Phe, formed from aspartic acid and phenylalanine.

It contains a peptide link that can be hydrolysed.

Aspartame also contains an ester link that can be hydrolysed.

Methanol is released when the ester link is hydrolysed.

The amino acids aspartic acid and phenylalanine are formed when the peptide link is hydrolysed.

A molecular model of aspartame.