Question

Why do most globular proteins contain alpha helices and beta sheets in the interior of the protein rather than regions of polypeptide that lack secondary structure?

Answer 1

All globular proteins contain substantial numbers of α-helices and β-sheets folded into a compact structure that is stabilized by both polar and nonpolar interactions . The globular structure is form spontaneously and is maintain by interaction side  chain interaction of amino acid. The hydrophobic amino allow the close packing as they ado not contact with water so buried inside the globular protein while Hydrophilic amino acid side chains lie on the surface of the globular proteins exposed to the water. Consequently, globular proteins are usually very soluble in aqueous solutions. The formation of helices and BETA -sheets is due to the role of hydrophobic interactions in designing the architecture of globular proteins.  Sheets are found to be more hydrophobic compared to helices along a protein chain. Both helix and -sheet frequencies are higher at higher average hydrophobicity, though the increase is steeper for -sheets. Hydrophobic sheets are more preponderant towards the N-terminus of the protein while more hydrophobic helices tend to occur only near the C-terminus of the protein. This also explains the burial of the more hydrophobic secondary structure in the protein core away from the surface, make them  less susceptible to mutations caused by environmental factors.