Two amino acids can get covalently linked by an amide bond, called peptide bond:
This bond is formed when the alpha carboxyl group of an amino acid reacts with the alpha amino group of the other amino acid, releasing a water molecule. For example, three amino acids can join in a tripeptide:
The alpha carbons of each amino acid alternate with the peptide bonds, forming the “backbone” of the polypeptide.
Lys-Ala-Ile (the sequence is always given starting by the amino acid whose amino group is free, called the N-terminal amino acid; in this case, it is Lys).
as in the above formula.
backbone and sidechains.
the peptide planes