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| the transformation of biolipids into biomarkers |
Molecular fossils that are stable under geologic condition mostly originate from lipids that were once functioning. Under the correct diagenetic conditions, these functionalized biolipids are reduced to their hydrocarbon skeletons in sedimentary environments.
What does this mean? We provide an example.
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adapted from Brock Biology of Microorganisms, courtesy of J.J. Brocks |
functionalized biolipid
In this picture, you see the cell membrane of a bacterium. Contained in this cell membrane are molecules called hopanoids, which function to strengthen the membrane. Hopanoids are powerful biomarkers because they are not (known to be) found in species of Archaea or eukaryotes. In this case, the specific hopanoid shown is a hopanepolyol. So, if we were looking at only modern systems, the presence of such a molecule would allow us to have a good idea about the source of this compound, without having to culture it or sequence its genome. Do note, however, without further information, the specificity of such an identification is very low.
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| the biomarker principle The transformation through diagenesis of a biolipid to a molecular fossil, or biomarker, is what we like to call the biomarker principle. As you see in the picture to the right, after burial and millions of years of abuse and pressure, the original biolipid (poor guy) loses some of its individuality, namely the hydroxyl (OH) groups on the chain. It does, however, retain the aforementioned hydrocarbon skeleton that allows geologists and geochemists like us to recover it and attempt to identify its source. Now, we call it a hopane, or geohopane. |
 figure courtesy of J.J. Brocks |
| This is just a single example. We have spent much, much time (much of several of our lives!) attempting to connect specific biomarkers with specific organisms, processes and depositional environments. Continue for information on classification of biomarkers, facility as indicators of paleoenvironmental conditions and experimental methods used to extract them. |
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