What causes a polypeptide to fold into an Alpha helix over a Beta pleated sheet
All the residues in a polypeptide chain tends to configure into their lowest potential energy state. except the peptide bond all the other bonds are free to rotate, alpha helix makes optimal use of internal H bonds. The overall structure is stabilized by H bond between the hydrogen atom attached to the electronegative nitrogen atom of peptide linkage and the electronegative carbonyl oxygen atom. The arrangement of amino acids in the peptide plays a very important role in forming alpha helix. Different combination of amino acids results in different combination of dihedral angels, hence it determines alpha helix conformation.