Hopanoids, biologically derived

Many coals contain extended chain (> 31 carbon atoms) hopanes and related compounds which appear to be diagenetically derived from the lipids of certain procaryotic organisms. Biologically produced hopanoids exclusively possess 173H, 213H stereochemistry. The... 

Hopanoids (the most common organic natural product on earth) must have been involved in the evolution of the biomembrane itself. All known membranes contain terpene derivatives, such as cholesterol or carotenoids, which belong to, or can be derived from, hopanoids. However, we still do not know their biological function. Their most commonly proposed mechanism is to regulate membrane fluidity. Another obvious effect is their influence on the lipid bilayer (or monolayer in the case of archaebacteria) curvature. The different types of hopanoids occurring will certainly favour the relative stability of either the planar or of the intrinsically curved membrane conformation. The ether lipids of archaebacteria, which are hopanoid derivatives, forming curved bilayers as discussed above, therefore provide evidence for cubosomes as the first organised form of life. 

---