Showing posts with label DNA. Show all posts
Showing posts with label DNA. Show all posts
Saturday, January 26, 2013
"Quadruple helix" DNA discovered in Humans Also, "Quadruple Helix" DNA is a Thing, Sort of
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| Digital rendering of the "crystal structure of parallel quadruplexes from human telomeric DNA." (Image credit: Wikipedia Commons) |
As I have attempted to make clear many times in the past, I know nothing. Meaning, I have no scientific education or expertise beyond the trivial bits of knowledge I learned in school, and the things I have managed to shove into my own brain over the years. But, obviously, I have a thing for science. And my interest in biology and genetics ranks just behind my fascination with all of the various forms of physics in the world. So usually I could at least say; Oh ya. That's a thing I heard about before, but wound up loosing somewhere in the background noise of my brain. But other than some vague recollections of futurist postulations about potentially engineering such a thing, or speculations about the genetics of as of yet unknown alien species, this time around- I got nothin. So my first thought upon reading the headlines "Quadruple helix DNA found in humans" was- well, that can't possibly be right. And, as is often the case, if you took the headline to mean the same thing I did anyway, it isn't what you think.
As you (hopefully) already know, DNA is the molecule which carries the genetic instructions that make you what you are. Fish, sheep, person, plant, virus, we all become what we become, because our DNA tells us too. DNA itself, is built from the pairing of four base chemicals, adenine (A), guanine (G), cytosine (C), and thymine (T). Once bonded together, these base pairs in turn attach themselves to a sugar molecule and a phosphate molecule, to form a nucleotide. Those nucleotides are in turn strung together along a sugar-phosphate backbone, forming the typical double stranded sequence of genetic information that is our DNA. Because these chemical bases always form specific parings -A to t and C to G- that
means, that as long as either side of the helix is copied during cell
division etc, the other half can always be replicated.It's all admittedly more complicated than that, obviously. But for our purposes here, I think that description pretty well illustrates why one might find the notion of 4 stranded DNA sequences... Surprising. Because, it's this redundancy of the double helix structure of our genetic code, that gives DNA superiority over it's likely predecessor RNA, as a means of successfully replicating complex biological sequences. So, taking all of the above into consideration. What the hell then is a quadruple helix? And what does IT do?
Previously seen only under laboratory conditions, a paper just published in the journal Nature Chemistry, based on a study conducted by scientists at the University of Cambridge, describes the first identification of these structures within human cancer cells. Unlike the double helix which controls our genetic development, G-quadruplexes appear to be non-coding genetic structures built from four guanine bases, which join together to form a square planar structure called a guanine tetrad.
Obviously, little is yet known for certain about the absolute purpose and function of these genetic structures. But The findings of the study seem to indicate a correlation between high concentrations of G-quadruplexes, and the process of cell division and replication; a theory which is supported by the finding that these structures appear more likely to occur in the genes of rapidly dividing cells, such as cancer. If their apparent genetic function proves true, researchers hope that removing the structures could potentially turn off the ceaseless replication that occurs within cancer cells, and experiments have already begun using specific molecules to isolate and capture the structures, so that they can do exactly that.
So, if like me, your initial reaction upon reading a headline containing the phrase "quadruple helix DNA" was to immediately start wondering about chromosome counts, evolutionary origins, and what not. First- we both REALLY need to get out more. Second, try not to be too disappointed. Because, while the actual nature of G-quadruplets is, admittedly, not as exciting as discovering an entirely new structure of DNA, potentially curing cancer is pretty good too, I think. And it' still undeniably cool, either way.
-CAINE-
Sources: Nature Chemistry, Phys.org
Saturday, August 13, 2011
Some of The Building Blocks of DNA May Have Come From Space
Artist concept credit: NASA's Goddard Space Flight Center/Chris Smith
By grinding up and analyzing samples of twelve carbon-rich meteorites, nine of which were recovered from Antarctica, a research group from NASA's Goddard Space Flight Center, in Greenbelt, Md, found both adenine and guanine; two of the primary nucleobases contained within our DNA, as well as hypoxanthine and xanthine; neither of which are used in the construction of DNA, but are utilized by other biological processes.
In two of the meteorites, the team also discovered for the first time, trace amounts of three molecules related to nucleobases (nucleobase analogues), purine, 2,6-diaminopurine, and 6,8-diaminopurine; two of which rarely appear in biology. According to Dr. Michael Callahan, lead author of a paper on the discovery appearing in Proceedings of the National Academy of Sciences of the United States of America;
"You would not expect to see these nucleobase analogs if contamination from terrestrial life was the source, because they're not used in biology, aside from one report of 2,6-diaminopurinecyanophage S-2L,"
While the presence of molecules not known to commonly appear in biology was a strong indication that the findings were not the result of contamination. Callahan's group further confirmed this fact by analyzing a sample of ice taken from Antarctica, where most of the meteorites in the study were found. The result showed much smaller concentrations of the nucleobases, as well as xanthine and hypoxanthine, all of which appeared in parts per trillion in the ice sample, as oppose to the parts per billion generally found within the samples taken from the meteorites. None of the Nucleobase analogues were discovered in the sample. Analysis of the soil taken from the surrounding area where one of the meteorites used in study fell in Austraila, also failed to detect those analogs.
In one final experiment designed to rule out terrestrial contamination and confirm the extraterrestrial origin of the molecules. Callahan's team was able to successfully generate all of the nucleobases and analogues found within the meteorite samples in a completely non-biological chemical reaction in the lab, using hydrogen cyanide, ammonia, and water. Showing not only that the find was almost certainly not the result of contamination, but more importantly, that chemical processes taking place within certain types of asteroids could potentially produce all of the molecules detected in the study.
If confirmed by further research, the findings of Callahan and his team could be a major step towards understanding the true origins of life on Earth. Particularly when considered along with previous research conducted by the team which detected amino acids, the molecules responsible for building proteins, within similar samples; as well samples taken from the Comet Wild 2 during NASA's stardust mission. All of which, adds to the growing body of evidence supporting the theory that the chemistry taking place within comets and asteroids is capable of generating the basic building blocks of essential biological molecules, and that life may owe it's existence, at least in part, to materials delivered from space via meteorite and comet impacts.
-CAINE-
Source: NASA
Image credit: NASA's Goddard Space Flight Center/Chris Smith
For a deeper explanation of the Nucleobases and nucleobase analogues, as well as the findings of his research, check out the following video from NASA, featuring Dr. Callahan.
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