The connection of proteinogenic amino acids to peptides and proteins proceeds through condensation reactions (loss of water) between the carboxylic groups and the amino groups.

The carbon atoms of the peptide groups are sp²-hybridized (bond angle: 120°). Two amide bonds are connected by sp³-hybridized building blocks (bond angle: 109.5°). This prevents rotation around the amide bond; after the third bond, the peptide chain is forced to adopt a helical conformation.

The resultant helix is further stabilized by hydrogen bonds between the side chains. The typical motif of the alpha-helix is formed.