Final answer:
Option C is the correct answer. The amino acids likely to be found on the surface of a transmembrane protein in the region contacting the fatty acyl chains are typically hydrophobic, such as leucine (L), methionine (M), and isoleucine (I). Soluble proteins have hydrophilic surfaces with polar or charged amino acids, while their interiors are hydrophobic. In lipid bilayers, proteins have non-polar amino acids in their membrane-spanning regions.
Step-by-step explanation:
The amino acids that might be found on the surface of a transmembrane protein, in the region contacting the fatty acyl chains, are typically hydrophobic. This means they are non-polar and have a tendency to repel water. From the options presented, the amino acids leucine (L), methionine (M), and isoleucine (I), which are part of option C (T, L, M, I), are all hydrophobic and would likely be found in the lipid bilayer contact regions of transmembrane proteins.
For a soluble protein's surface, you would expect to find hydrophilic (water-attracting) amino acids which are usually polar or charged. These amino acids interact favorably with the aqueous environment. In contrast, the interior of soluble proteins often contains non-polar, hydrophobic amino acids that are shielded from water. When it comes to proteins that are embedded in a lipid bilayer, the amino acids within the membrane-spanning region are typically non-polar, allowing them to interact with the hydrophobic core of the lipid bilayer, while the portions of the protein that protrude out of the membrane into the aqueous environment will generally have polar or charged residues.