Useful Links!

http://helixweb.nih.gov/structbio/basic.html

http://www.ccp4.ac.uk/                                            

http://www.ccp4.ac.uk/html/symlib.html                             ftp://ftp.ccp4.ac.uk/mdw/csym/csym_only.c

http://www.peptide2.com/mainNew_amino_acid_converter.php