The Linkages of Proteins, Nucleic Acids, and Polysaccharides

As stated previously, polymer stereochemistry depends critically upon the structures of the monomers and how they are assembled. No new stereocenters are produced when amino acids are combined to make proteins, or nucleotides are combined to make nucleic acids. This is because the linkages created in forming the polymers are not stereogenic. The same is not true for polysaccharides, where the newly formed anomeric center is stereogenic. We will consider these three types of biopolymers separately. 

The newly formed peptide bond is not a stereogenic unit, so amino acid polymerization is in some ways different than propylene polymerization. However, as we noted earlier in 

Basic stereochemical issues in protein structures. A. The conventional representation of a protein chain, and an alternative representation Aat emphasizes the isotactic nature of the polymer. B. S-cis and. s-trans geometries in a conventional peptide bond and in a peptide bond involving proline. 

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