Elementary plant Biochemistry and Biotechnology (2+1)

Secondary structure

 
• Secondary structure refers to the steric relationship of amino acids that are close to one another in the linear sequence.
• The folding of a linear polypeptide chain occurs to form a specific coiled structure. Such coiling or folding is maintained by hydrogen bonds and hydrogen bond is the only bond responsible for secondary structure.
  
• X-ray studies of several polypeptides by Linus Pauling and Robert Corey revealed that the peptide group has a rigid, planar structure which is a consequence of resonance interactions that give the peptide bond a 40% double bond character.
• Peptide groups mostly assume the transconformation in which successive C2 atoms are on opposite sides of peptide bond joining them.
• The cis configuration creates steric interference.
• If a polypeptide chain is twisted by the same amount each of its C atoms, it assumes a helical conformation