Twisted liquid crystalline supramolecular arrangements in morphogenesis.

Supramolecular assemblies following liquid crystalline cholesteric geometries have been described in biological systems from optical properties observed in polarized-light microscopy and structural data obtained in electron microscopy. Major biological macromolecules are discussed, including structural polymers of the extracellular matrix, genetic material in nuclei and chromosomes, and proteins of the cytoplasm. The liquid crystalline assembly properties of biological polymers have been demonstrated by experiments in vitro with molecules at basic structural levels, such as molecular chains of cellulose and chitin, triple helices of collagen, and double helices of DNA, and also with entities at higher states of organization as they appear in cells and tissues, such as cellulose and chitin crystallites, and collagen fibrils. It appears that the building of cellular and extracellular edifices implies self-ordering processes of the liquid crystalline type and that the study of these mesomorphic states will help resolve basic questions about the structure and morphogenesis of densely packed biological structures.