Lipid world hypothesis

These successes in the area of precellular structures led Daniel Segre et al. from the Weizmann Institute in Rehovot to publish the lipid world hypothesis together with Deamer. The authors are of the opinion that the (more probable) lipid world determined chemical and molecular evolution on the primeval Earth prior to the (less probable) RNA world . Further development stages (or worlds ) finally led to biogenesis (Segre et al., 2001). 

The Lipid World hypothesis states that polar hydrocarbons formed in a prebi-otic Earth, or originated from extraterrestrial meteoric sources, and then went on to aggregate into vesicles. These vesicles then capture chemical species at random in some cases the concentrating effect of the vesicle would facilitate chemical reactions and some of these would eventually lead to self sustaining chemical reactions. Eventually protein-based enzymes would emerge that could synthesize lipids and the entire system would then become symbiotic. 

An alternative candidate for a cell membrane is one composed of mostly hydrophobic molecules that would spontaneously aggregate if suspended in water. It is important that the molecule is not entirely hydrophobic, like hexane or benzene, as some part of it must be solvated if it is to aggregate with others to form a structure capable of encapsulating other species. Candidates for this type of molecule are the lipids and related compounds. The formation of protocells by lipids has been discussed previously as part of the Lipid World hypothesis. In the context of compartmentalization it is important to consider how such an aggregate could evolve. 

TCPM is reported in samples from areas from all over the world. A reason for this ubiquitous occurrence may be the presence of the 4-chlorophenyl rings in the compound, which are also found in p,p -DDT and its metabolites p,p -DDD and p,p -DDE, which are also very persistent contaminants. This structure is also found in bis(4-chlorophenyl) sulfone, which was recently reported as a new persistent contaminant [14]. The 4-chlorophenyl structure is apparently very resistant to transformation in the environment. Only in Mediterranean fish samples were TCPM and TCPMe not detected at a level of 1 pg/kg lipid weight. TCPM concentrations on a lipid weight basis decrease from 180 pg/kg to 360 pg/kg in eel from the river Rhine delta, to 40 pg/kg in cod liver from the southern North Sea, and to 6 pg/kg in cod liver from the northern North Sea (Table 2). This suggests a relationship between high TCPM concentrations and densely populated, industrialized areas. High TCPM concentrations in samples from the Baltic Sea and Lake Ontario and low TCPM concentrations in samples from Antarctica confirm this hypothesis. 

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