Rotation about the angles Phi and Psi

 View Chime version of this demo
 Obtain chime/ ISIS Draw

The two pictures at the top represent the same structures with two different models. The first is a space filling model demonstrating the amount of space required for each atom. The second is a stick model to help you see the angles as you rotate the bonds. You may select to rotate either Phi or Psi. The currently select angle is also displayed on the plot of Phi vs. Psi. On the Phi/Psi plot..... The regions that are white are ANY allowed for any amino acid. The pink regions are Phi/Psi angles that are not allowed for all those amino acids which have a b-Carbon (ie. all but glycine). Notice: the pink regions are symmetrically placed across the graph while the dark purple one are assymmetrical! The Dark purple regions are those that ARE allowed for all amino acids except proline. In Proline Phi is restricted to angles of about -60 degrees while Psi is "freely rotatable".In the pink regions indications such as "<--- R-O1---> mean that The b carbon of the side chain and the oxygen atom of the amide collide in this region. Look for these collisions on the pictures as you rotate the bonds.As you change the angles, a blue bar represents a rough idea of where you are on the plot.The circle on the plot labeled "a" represents the angles that when several consecutive amin acids have these angles an a-helix structure is observed.
the circles labeled "A" and "P" represent the angles that when several consecutive amin acids have these angles an b-sheet structure is observed.