Hopanoids
The hopanoids (stress on the penultimate vowel: Hopano i de ) are membrane-reinforcing molecules. They are extremely stable triterpenes and consist of 4 six-membered rings, one five-membered ring and residues of different chain lengths. They have a structural similarity to steroids .
distribution
In bacteria , instead of the steroids found in eukaryotes , hopanoids serve as membrane enhancers. Exceptions to this are the methanotrophic bacteria, which belong to the proteobacteria , and the mycoplasmas , which belong to the gram-positive bacteria. Like eukaryotes, these have steroids instead of hopanoids, which they cannot synthesize themselves but take in from outside.
Hopanoids, which occur in cyanobacteria , were found in stromatolites in Australian rock strata that are 2.7 billion years old, and are among the oldest evidence of the internal structure of early living things.
As far as is known, hopanoids are not found in archaea .
swell
- J. Brocks, G. Logan, R. Buick, R. Summons: Archean molecular fossils and the early rise of eukaryotes. Science 285/5430/1999, pp. 1033-1036, PMID 10446042