Membrane Lipids and the Origin of Life

Abstract

There are two major types of amphiphilic lipids found in the plasma membranes of all living cells. The acylglycerol ester derivatives of ordinary bacteria and eukaryotes,and the isopranyl ether derivatives of Archaebacteria. Due to the importance of membranes in the origin of life and to the limited work done in this field we have undertaken experiments on the prebiotic synthesis of the building blocks of membrane lipids of prokaryotes and eukaryotes, and we have studied the less known membrane lipid components of Archaebacteria. Concerning the former, we have been successful in synthesizing fatty acids, glycerol, glycerophosphate, mono-, di- and tripalmitoyl glycerol esters and the corresponding phosphatidic acids. Glycerol has been obtained by reduction of the products from the formose reaction. Furthermore, under the prebiotic conditions of an evaporating pond model and using cyanamide as a condensing agent we have synthesized glycerol phosphate and all the other complex lipids. These amphiphilic molecules have the ability to self-assemble into stable bilayered microvesicles which show structure and functions similar to cell membrane lipid bilayers. Concerning the Archaebacteria (Methanogens, Halophiles, Sulfolobus and Thermo-plasma) we have analyzed their membrane lipids and found them to be derivatives of diphytanyl glycerol diethers or di-C₄₀-isopranyl diglycerol tetraethers. Such a unique membrane ether lipid composition is ideally suited for stability to the high temperature and other extreme environmental conditions of archaen times. This and other evidence suggests that the extant Archaebacteria evolved from a common anaerobic ancestral line when the primitive Earth was evolving from anoxidic to oxidic conditions at about 3.7 Aeons ago.