Question

Residues such as valine, leucine, isoleucine, methionine and phenylalanine are often found in the interior of proteins, while arginine, lysine, aspartic acid and glutamic acid are often found on the surface. Suggest a reason for this. Where would you expect to find glutamine, glycine and Alanine?

Answer 1

Proteins consist of a hydrophobic inner consisting of hydrophobic molecules.Why hydrophobic is in the core because hydraphilic parts (charged molecules) of proteins are attracted towards protein surface which is in interaction with the surrounding solvent (aquous medium). They form hydrogen bonds with surrounding aquous medium and tend to stabilize the protein structure.

The hydrophobic amino acid constituent parts of the protein tend to repel the aquous environment and are therefore pushed in the interior of the protein that is the core part of protein.

Now valine, leucine, isoleucine, methionine and phenylalanine are non polar and thus hydrophobic, so are buried inside the protein core.

On the other hand, arginine, lysine, aspartic acid and glutamic acid polar and charged, thus are attracted towards solvent aquous environment and are involved in hydrogen bonding remaining on the surface of the protein.

Glycine and Alanine are non polar and thus hydrophobic, therefore these two will be found in the protein inner core, whereas Glutamine is charged and hydrophilic, so will be found on the protein surface.