These groups include some straight chains, aromatic groups, acids, and bases. Some of these groups bind quite well to water, these are the hydrophilic groups. Others do not bind at all to water, these are called hydrophobic groups. The stereochemistry of amino acids are important. All amino acids can exist in D and L forms.
Amino acids incorporated into protein structures are of the L form .
Amino acids link together between the amide and carboxyl groups. Two amino acids bind together and eliminate water resulting in a peptide link. What is left is referred to as an amino acid residue. If this chain becomes very long, it is then called a polypeptide. All proteins are polypeptides of a defined sequence of amino acids.