Solutions to Exercise 2
Bad contacts observed when varying phi and holding psi constant at -60 degrees (as an example):
| Phi | Contacts | OK? |
| 0 | 1@O is 2.0 Å from 3@N. | Unacceptable |
| 60 | 1@O is 2.2 Å from 3@N. | Unacceptable |
| 120 | 2@CB is 2.3 Å from 1@O. | Unacceptable |
| 180 | 2@CB is 2.9 Å from 1@O. | Acceptable |
| -120 | No problem distances. | Acceptable |
| -60 | No problem distances. | Acceptable |
Note that this is a reasonable reflection of the Ramachandran plot, in that there are acceptable values of phi between -30 and -180 degrees when psi is set at -60 degrees. Note that if a tripeptide of glycine were used for this study, however, that this region of stability would extend to positive regions of phi, perhaps between 60 and 180 degrees, providing mirror symmetry about the phi = 0 axis.