Draw all the atoms in a trans peptide linkage from C alpha of one amino acid...

Draw all the atoms in a trans peptide linkage from C alpha of one amino acid to C alpha of the next amino acid (do NOT include atoms of the side chains) and indicate possible resonance structures.

Expert Solution

Amino acids in polypeptide chains are linked by peptide bond. Linus Pauling and Robert Corey analysed the geometry and dimensions of the peptide bonds in the crystal structures of molecules. Their results are summarised in the diagram where the bond lengths are shown in Angstrom units. Bond angles in degrees are also shown for the peptide N and C atoms. (Refer diagram 1)

Note that the C-N bond length of the peptide is 10% shorter than that found in usual C-N amine bonds. This is because the peptide bond has some double bond character (40%) due to resonance which occurs with amides. The two canonical structures are shown in the diagram (refer diagram 1)

As a consequence of this resonance all peptide bonds in protein structures are found to be almost planar, ie atoms C-alpha(i), C(i), O(i), N(i+1) H(i+1) and Calpha(i+1) are approximately co-planar. This rigidity of the peptide bond reduces the degrees of freedom of the polypeptide during folding. (refer diagram 2)

queen_honey_blossom answered 2 years ago

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