Dihedral/Dihedral angles in proteins

The model displayed on the right is a tripeptide (Trp₃₄–Glu₃₅–Ser₃₆ within the protein lysozyme). This page illustrates the meaning of phi (ϕ) and psi (ψ) angles, both around the alpha carbon of the central residue (Glu₃₅).

phi (ϕ) is the angle between the planes displayed as (1) and (2)

psi (ψ) is the angle between the planes displayed as (3) and (4)

(planes 2 and 3 coincide)

You can run animations that continuously rotate the model changing one of the angles. Bright magenta cylinders are displayed where neighbour atoms collide (hence there is an unfavourable conformation for those particular ϕ, ψ values).

animation, and then:

animation, and then: