Cellular organelles and lipids

These structural and biochemical studies indicate that the internal structure of the cell is a complex system of macromolecules which are organized into organelles for function. These organelles consist of complicated internal membranes, the structure of which in molecular dimensions is best represented by a double layer of lipid and protein, referred to as the unit membrane (Fig. 3b, 3d, 4d, 5d). Such a structure provides large surface areas for the orientation of pigment molecules as in the photoreceptors (Fig. 8) and sites for enzymatic reactions. Since these membranes contain high concentrations of lipids, their synthesis and molecular organization become important. Such ordered organelle structures behave like liquid crystals for they undergo phase transitions from ordered to disordered states which depend upon temperature and concentration. The determining of the kinds and distribution of the fatty acids in a variety of cells may be an approach for developing phylogenetic relationships as well as biochemical patterns in the evolution of the plant → animal. For a deeper understanding of the biological mechanism however, newer tools need to be developed to study the subtleties in the chemistry of the cell and its organelles in the living state.