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Observation by phase-contrast microscopy using a temperature-controlled stage (8) revealed f sharp T m s ; melting was usually completed over a one degree range, (b) Titration of micellar fatty acid solutions from pH 10, at T m+5°C, resulted in the formation of vesicles at a precise pH. T m for octanoate was estimated to be 5°C. surface temperatures in regions of the Earth which are now temperate probably exceeded 70°C (see section II-E). Thus, while short-chain (

Deamer 3 5 Department of Zoology University of California at Davis Davis, California I. INTRODUCTION All free-living organisms and many viruses have lipoprotein membranes. These membranes serve many functions, including the separation of cell contents from the environment. This allows the selective storage of metabolites and products, the removal of waste products, and the formation and maintenance of ion gradients to do work. Genetic material may attach to membranes to facilitate genome distribution to progeny during cell division.

5 /am). (c) Phospholipid vesicles (same as in fig. 6 d ) , fixed with λ% osmium tetroxide before staining; magnification same as in b.. Prebiotic lipid membrane assembly 51 Figure 14. Freeze-fracture of vesicles. Bar=1 μπι. Polar lipids were dispersed in phosphate-buffered 25? glycerol at 50°C (5 mg/ml lipid). Freeze-fracture was performed as in figure 6. In b, note the vesicular inclusion within a larger liposome which appears unilamellar. IV. LIPID CONCENTRATION REQUIRED FOR MEMBRANE FORMATION The "primeval soup" was probably fairly dilute, probably containing less than 10 mg/ml total organic material (37).