Describe the resonance in peptide bonds and discuss its significance

The following link is from an educational website pertaining to
peptide bonds (the information I have independently verified as being
correct--I have a biology degree and still have some biochemistry and
organic chemistry texts):

http://www.dentistry.leeds.ac.uk/biochem/lectures/peptide%20bonds/peptide%20bonds.htm

"Peptide bond resonance:
The peptide bond is usually drawn as a single bond. However, it has
about 40% double bond character due to the existence of resonance
structures. The possible resonance structures are shown for the
dipeptide Ala-Ser:"

[See figure on [ http://www.dentistry.leeds.ac.uk/biochem/lectures/peptide%20bonds/peptide%20bonds.htm
], under the "Peptide Bond Resonance" header, near page bottom].

"The partial double bond character of the peptide bond means that it
is locked and is not free to rotate. Free rotation (within the limits
of steric hindrance caused by the side chains) occurs in all the other
bonds."

Google search strategy: 

Keywords, "peptide bond resonance"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=peptide+bonds+resonance,

"peptide bonds" ://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=peptide+bonds++&btnG=Google+Search

Good luck in continuing your inquiries!

~omniscientbeing

Thank you. Could have been more indepth perhaps?!