Saturday, January 26, 2013

"Quadruple helix" DNA discovered in Humans Also, "Quadruple Helix" DNA is a Thing, Sort of

Digital rendering of the "crystal structure of parallel quadruplexes from human telomeric DNA." (Image credit: Wikipedia Commons)
So here's an unbelievably fascinating and cool thing that I had no idea was actually a thing: quadruple-Helix DNA, or G-quadruplexes.

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.


Sources: Nature Chemistry,

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