As polypeptide folds, hydrophobic R—groups are brought into close proximity as they are excluded from water. Many amino acids like valine, alanine, leucine, isoleucine, methionine, tryptophan, phenylalanine, and tyrosine have side chain or R groups which are hydrophilic. These R—groups combine together with the removal of hydrogen and form linkages between various segments of chains. In addition to this, hydrophobic bonds are involved in protein interaction.