A peptide is composed of amino acids. In general, there are 20 different amino acids
commonly found in peptides and proteins. Each of themis formed by an amino group,
a carboxyl group, a central CH group (the carbon of this central CH group is usually
called α-carbon or C
) and a specific side chain (Figure A.1, Appendix A). The
sequence of C
α
α
atoms connected through covalent peptide bonds, including the Nterminus
(free NH2 initial group) and C-terminus (free COOH final group) is called
the peptide backbone. It is the main structural part of the peptide that determines
its overall geometric properties. The side-chains of a peptide define its physical and