Thermodynamic considerations on polysaccharide functions. Polysaccharides came first

The molecular evolution of polysaccharide functions are considered from the perspectives of structure, thermodynamics and proposed biological values. The main ideas emerging from this thermodynamic approach are the following. First, processing food systems that typically contain denatured non-specifically interacting biopolymers, are a physical chemical model of the primordial soup. Second, polysaccharides were the first biopolymers. They were incompatible with one another and other proto-biopolymers. Third, cross-linking of dissimilar macromolecules would result in conjugates and could explain the parallel co-evolution of proto-biopolymers. Finally, self-reproducing conjugates would cause a phase separation within the primordial soup leading to a concentration of conjugates within dispersed phase particles whose properties could then have evolved into proto-cells. Polysaccharides, due to their incompatibility with proteins, had to be exported from the cytoplasm to form the cell-walls and exopolysaccharide protective capsules around primordial cells. The thermodynamic properties of polysaccharides and their effects on complex biopolymer mixtures became responsible for the ecological defense of cells from foreign macromolecules and their simultaneous nourishment by foreign molecules. This coexistence of protection and consumption of biomolecules by cells corresponds to the dependence of cells on the composition and structure of polysaccharides. The use of starch as a source of energy, and of pectin and cellulose as plant cell wall materials are a logical result of divergence of structure from a common ancestor based on the plagiarism of genetic systems for biopolymer biosynthesis. (C) 2003 Elsevier Ltd. All rights reserved.