[negss]

Where is Proline residue located? Would it be found on both helix and sheets or on helix only? and where on the structure would it be found?

[Babcock_Hall]

Can you explain what you have learned so far in a little more detail?  Proline at position n restricts the available phi/psi dihedral angles of the preceding (n-1) residue in the polypeptide chain.  This has important consequences for its preferred secondary structure.  It also lacks a hydrogen atom on nitrogen; therefore, proline residues cannot donate H-bonds.  Regular secondary structure such as the alpha helix and the beta sheet have a regular pattern of hydrogen bonding between the carbonyl oxygen of one residue (the acceptor) and the amide group of a different residue (the donor).