[BiO BB] Ramachandran plot

[merin]

Hello all,
  Can you please help me?
I'm very much interested in Ramachandran plot.
I searched a lot for information relating to its applications,but got
very little information.
Can you please help me in this regard?
1)What are the important applications of Ramachandran plot in structural
Bioinformatics?
2)If you change an amino acid in the protein sequence,what precise
effect does it have on the plot and what are the applications in this
regard?
3)Does it have any application in Homology modelling?

merin