When people think of DNA, they usually think of the familiar double-helix shape so familiar from illustrations and seventh-grade textbooks.
But DNA actually comes in various shapes and sizes, as Sapna Parikh explains in today's DNews dispatch. In fact, a team of researchers in Sweden recently discovered a rare kind of four-strand DNA in yeast, which may lead to new insights on the development of cancer and certain degenerative diseases.
The usual spiraling DNA shape actually comes in three varieties, designated A, B and Z. B-DNA is the familiar one -- the ladder twisting to the right -- and it's the most common in living cells. A-DNA looks similar, but has a wider spiral. Z-DNA, prone to surly contrariness, twists the other way and appears to play a role in transcription, the process by which genetic information is copied.
A fascinating study in 2015 revealed that longer DNA strands, packed tight into a cell's nucleus, actually twist and morph into bizarre tangles of genetic information. Using powerful microscopes and computer simulations, scientists found all manner of weirdness in this so-called supercoiled DNA, including knots, figure-eights and other strange shapes.
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The four-strand DNA from the Sweden study, meanwhile, is called G-Quadraplex DNA, or G4 DNA. The "G" refers to guanine, one of the four bases that holds DNA together and spells out our genetic code. It's been studied in yeast, maize and other living cells, but scientists are hoping to further analyze the variant in humans.
That's because G4 DNA appears to play a role in the body's process of regulating cancer. We know that G4 structures are present in genes that regulate cell division. If we could target G4 DNA with specific drugs, we might be able to "turn off" cancer at the source.
Double Secret Bonus Trivia: According to computer models from the 2014 study, a full set of supercoiled DNA, untangled and stretched out, would measure more than a meter in length.
-- Glenn McDonald
Discovery News: Supercoiled DNA: Double Helix Gone Wild
Eureka Alert: Supercoiled DNA is far more dynamic than the 'Watson-Crick' double helix
BBC: 'Quadruple helix' DNA seen in human cells