Editing Amino acid (section)

==== Hydrophobic side chains ====

Nonpolar amino acid interactions are the primary driving force behind the processes that [[Protein folding|fold proteins]] into their functional three dimensional structures.<ref name="Garrett-2010" /> None of these amino acids' side chains ionize easily, and therefore do not have pK<sub>a</sub>s, with the exception of [[tyrosine]] (Tyr, Y). The hydroxyl of tyrosine can deprotonate at high pH forming the negatively charged phenolate. Because of this one could place tyrosine into the polar, uncharged amino acid category, but its very low solubility in water matches the characteristics of hydrophobic amino acids well.