Sterol multiple functions

Now, the question which has motivated much of the recent work In my laboratory, and which I should like to discuss here, is this What really Is the reason why certain sterols accumulate Is one sterol as good as another Are we just observing a more or less random distribution based on chance mutations Or is a selection operative, a mating of structure to function, suggesting, for Instance, in squash the existence of multiple functions for sterol ... 

Rodriguez RJ, Low C, Bottema CDK, Parks, LW. Multiple functions for sterols in Saccharomyces cerevisiae. Biochim Biophys Acta 1983 837 336-343. 

Lipids have several important functions in animal cells, which include serving as structural components of membranes and as a stored source of metabolic fuel (Griner et al., 1993). Eukaryotic cell membranes are composed of a complex array of proteins, phospholipids, sphingolipids, and cholesterol. The relative proportions and fatty acid composition of these components dictate the physical properties of membranes, such as fluidity, surface potential, microdomain structure, and permeability. This in turn regulates the localization and activity of membrane-associated proteins. Assembly of membranes necessitates the coordinate synthesis and catabolism of phospholipids, sterols, and sphingolipids to create the unique properties of a given cellular membrane. This must be an extremely complex process that requires coordination of multiple biosynthetic and degradative enzymes and lipid transport activities. 

Based on compound-specific studies, Pearson et al. (2001) have reported that many of the lipid fractions from SMB sediments in the surface to 8 cm horizon like alcohols, sterols and fatty acids derive from marine euphoric zone primary production or subsequent heterotrophic consumption of this biomass. The ages of corresponding fractions in our sample from SMB, but from deeper horizon (30-50 cm), are much older to be attributed entirely to such an origin. This reflects multiple sources of organic matter contributions to the sediments (as discussed above) as a function of rime. 

---