Proline is the only amino acid with a secondary amine rather than a primary amine at its α-carbon position. A peptide bond forms a covalent bond between the carboxyl carbon of one amino acid and the amino nitrogen of another amino acid, releasing a water molecule in the condensation reaction. Peptide bonds link amino acids together into polypeptide chains or proteins.

6. Prolina - único aminoácido cuya α-amina es
una amina secundaria en lugar de una amina
primaria.

15. Figure 3-1. A peptide bond. This covalent
bond forms when the carbon atom from the
carboxyl group of one amino acid shares
electrons with the nitrogen atom (blue) from
the amino group of a second amino acid.
As indicated, a molecule of water is lost in
this condensation reaction.