Final answer:
Leucine side chain would most likely be found in the interior of a protein in contact with nonpolar side chains.
Step-by-step explanation:
The distribution of amino acids in a protein dissolved in water reflects the polarity of their side chains. Leucine, being a non-polar amino acid, will most likely be found in the interior of the protein, where it interacts with other nonpolar side chains. This hydrophobic environment is energetically favorable, as leucine side chains can avoid contact with water. Conversely, polar and charged amino acids will typically be found on the surface of a protein, where they can interact with the polar water molecules.
In the context of a protein embedded in a lipid bilayer, such as those in cell membranes, the distribution of amino acids would be different. Here, the surface of the protein that interacts with the fatty acid tails of the lipid bilayer is likely to feature non-polar amino acids, while the regions that interact with the aqueous environment inside and outside the cell will feature polar and charged amino acids.