Probably many people are already aware of this, even in these times where contempt for science is ever more fashionable, but the mechanism by which the information contained in one's genome, which is chemically DNA, into actual proteins involves RNA. "Messenger RNA" is produce via a biochemical reaction with dissociated DNA strands, and carried to organelles in cells called "ribosomes" where proteins are synthesized. Proteins do most of the "work" associated with life, including human life.
DNA's structure in turn, is famously a double helix, and this helix contains "grooves," that have important ramifications for the chemistry of this famous nucleic acid, particularly with respect to certain classes of planar molecules that can insert into these grooves, sometimes under circumstances in which they actually covalently bond to DNA's functional groups. Some types of cancer are believed to be induced by these sorts of changes to nucleic acids after the insertion of planar species.
RNA also is a helical molecule, but the difference between the deoxgenated ribose sugar in DNA and the oxgenated form in RNA strongly affects these types of interactions.
I apologize if this is all too basic or all too glib...
I will very briefly refer to a paper that touches on this matter of planar molecules. It is found in a recent issue of Environmental Science and Technology, a publication of the American Chemical Society, the world's largest scientific organization, in this very short diary, in case someone is interested. It concerns the changes to RNA induced by the very high concentrations of polychlorinated biphenyls found in "killer whales." The link to the abstract follows below:
PCB-Associated Changes in mRNA Expression in Killer Whales (Environ. Sci. Technol. 2011, 45, 10194–10202).
Here's some excerpts from the text:
Killer whales (Orcinus orca) in the Northeastern Pacific Ocean are among the world’s most polychlorinated biphenyl (PCB)- contaminated marine mammals, reflecting in part their long lifespan, high trophic level, and limited ability to metabolize recalcitrant contaminants.1,2 Along with reduced abundance of their preferred prey (Chinook salmon), and noise and disturbance, high levels of endocrine-disrupting contaminants are touted as conservation threats to the resident killer whale communities.3 The fish-eating Northern and Southern resident populations are listed under Canada’s Species at Risk Act (SARA) as ‘threatened’ and ‘endangered’, respectively, and the marine mammal-eating transients have been listed as threatened
(http://www.sararegistry.gc.ca/...). The transboundary Southern residents are also listed in the USA as ‘endangered’ under the Endangered Species Act (http://www.nwr.noaa.gov/...
Killer-Whales/ESA-Status/Orca-Recovery-Plan.cfm). While logistical, legal, and ethical constraints limit toxicological research in free-ranging killer whales, evidence fromother marine mammals4,5 would suggest that PCB-related effects including immunotoxicity,
endocrine disruption, and reproductive impairment represent a distinct concern for killer whales.3
Mmmm...ethical concerns, eh?
Well, be that as they may, the authors, well, let them say for themselves...
In the present study, we obtained biopsy samples from 35 killer whales for which detailed Supporting Information is available (i.e., age, sex, and feeding preferences). These samples were used to isolate cDNA and develop species-specific QPCR assays to determine abundance profiles for mRNA transcripts encoding protein products representative of endocrine and immune functions and chemical detoxification. This enabled assessment of the relationship between mRNA abundance
profiles in killer whales and the concentrations of PCBs, the primary contaminant of concern in this species.
So, um, how'd they get these biopsy samples?
Tissue Sample Collection. Skin and blubber samples were obtained by biopsy dart from killer whales frequenting the coastal waters of central and northern British Columbia, Canada, as previously described.1 Biopsies were taken from the region
immediately posterior to, and below, the dorsal fin using a lightweight pneumatic dart system.20 Visual confirmation of identity, age, and sex were based on photographic catalogues of resident and transient killer whales (http://www.pac.dfo-mpo.
gc.ca/science/species-especes/cetacean-cetaces).
Biopsy dart?
The analytical chemistry in this paper is quite impressive. The authors identified 136 PCB species in the whale blubber via GC-MS in more than 70% of the whale samples, and another 35 cogeners in less than 70% of the whale samples.
Sixteen RNA transcription systems in killer whales were evaluated, and of these the expression of five of them were statistically shown to correlate with high concentrations of PCB's.
The authors note that they are unsurprised by this, to wit:
Evidence from carefully controlled laboratory and semifield studies demonstrates the ability of PCBs to disrupt endocrine function, immune function, and metabolic processes, leading to developmental, reproductive, and immune system impairment.24 The PCA and subsequent univariate and multivariate evaluations presented herein identify five particular gene transcripts that have strong associations with PCBs in free-ranging killer whales.
PCBs were historically considered "green" and "inert" insulating agents and were widely used as insulating fluids in transformers in electrical grids and in other types of devices.
They have now been largely supplanted by the use of sulfur hexafluoride, which as luck would have it is one of the most powerful greenhouse gases known. (Sulfur hexafluoride is also used to manufacture semi-conductor materials, and, interestingly, as insulators in swell "green" thermally isolating windows that rich people put on their McMansions to feel better about themselves.)
Speaking of electronic waste, another set of planar molecules that may have some toxicological niceties about them are the PBDE's, polybrominated diphenyl ethers. These are commonly used in electronic devices, like, um the computer that I am using to write this diary, just like a certain class of people burn coal to tell us how awful nuclear energy is.
Benzofurans, benzodioxanes and a host of other planar molecules are produced by, um, combustion, including the combustion of wood and other biomass, which is known to be involved in the enormous health risks associated with air pollution.
Anyway, about those whales, the authors are, um, concerned.
They write:
While toxicological research in endangered species is limited by inherent technical, legal, and ethical constraints, our biopsy based results from free-ranging killer whales provide compelling insight into the effects of one of the leading chemicals of global environmental concern. These results provide a stark reminder of the lingering health risks associated with persistent and bioaccumulative contaminants such as the PCBs, particularly in long lived, high trophic level wildlife.3 Although the population-level
consequences of our present observations are unclear, observations of increased mortality and reduced reproductive success in the highly contaminated southern resident killer whales, comprising fewer than 90 individuals, are of particular concern.63 Exposure to environmental chemical contaminants, diminished abundance of preferred prey (Chinook salmon), and disturbance by human activities bring into question the viability of small killer whale populations
Have a great day tomorrow.