Ten Things You Probably Didn't Know About DNA

Ten Things You Probably Didn't Know About DNA

by Robert T. Gonzales

It may be the basis of all life on Earth, but we're betting there's still a lot you don't know about deoxyribonucleic acid. Who discovered it? What makes it "right-handed"? And what does it have to do with LSD? Find out after the jump.

10. James Watson and Francis Crick did not discover DNA

Neither did Rosalind Franklin or Maurice Wilkins, for that matter. In actuality, the credit for discovering DNA goes to one Friedrich Miescher. In 1869, the Swiss biochemist was inspecting the pus on used surgical bandages (yay, science!) when a substance he didn't recognize passed into his microscope's field of view. He called the substance "nuclein," because, he noted, it was located within the nuclei of cells.

9. Good Call, Miescher

Which is funny, because you can actually find a fair bit of DNA in mitochondria, as well. What's interesting, though, is that out of all your DNA, it's the stuff in your nuclei that play the most important role from a hereditary standpoint; remarkably, Miescher would later speculate in a letter to his uncle that this mysterious "nuclein" might actually play a role in heredity.

8. It took decades to prove Miescher's hunch was right

Miescher's insight was years, if not decades, ahead of its time. By the turn of the 20th century, scientists had begun to strongly suspect that chromosomes — densely packed structures of DNA and protein — were involved in the transmission of traits from one generation to the next, but it wasn't until researcher Thomas Hunt Morgan showed that molecular differences in chromosomes actually corresponded to heritable physical characteristics in fruit flies that anybody truly appreciated the fundamental role of said chromosomes in the transfer of genetic information.

7. Wait... what genetic information?

What's interesting about the phrase "genetic information" is that even as late as 1933, the year Morgan received a Nobel Prize for his groundbreaking work on chromosomes, many scientists still doubted the existence of so-called "genes" — information, presumably housed within chromosomes, that gave rise to the physical traits Morgan had observed in his experiments. At the time, Morgan wrote that there was no consensus "as to what the genes are — whether they are real or purely fictitious."

The concept of genes only really found its footing in 1944, when molecular biologist Oswald Avery (pictured here) showed thatgenes were not only real, but that they were composed of DNA (and not, for example, proteins, which — also being contained in chromosomes — many scientists had assumed comprised our true "genetic" blueprint).

6. LSD May have played a role in the discovery of DNA's structure

Just nine years after Avery's discovery, James Watson and Francis Crick published an article in Nature describing the double helical structure of DNA — a structure which, according to some accounts, Crick claims to have perceived while high on LSD.

5. Why is it Watson and Crick and not Crick and Watson?

Joe Hanson actually posed this excellent question last week on It's Okay to be Smart:

How did they decide whose name would come first on their paper? That's where we get the comfortable meter of their paired and classic name pairing from. I mean, did they flip a coin? It was a fairly even collaboration, and I don't know why their names weren't on the paper in alphabetical order.

I mean, just think of that. What if it had been Crick & Watson? A huge part of the biological lexicon would be changed:

"Well Steve, you can clearly see the canonical Crick & Watson base-pairing there in the hairpin."

It turns out they did just flip a coin, though to hear James Watson tell it, it sounds like he felt he deserved to be first author, anyway.

4. DNA is Right-Handed

When you see DNA depicted as a double helix, you can clearly see that its structure is twisted. That twist makes DNA a "chiral" molecule, meaning it is asymmetric in such a way that a DNA molecule and its mirror image are not superimposable. Examples of chirality are everywhere. Take your hands, for example. For all intents and purposes, your left hand and right hand are mirror images of one another, but no matter how you twist or position either hand, you'll find that it is impossible to orient the two of them in exactly the same way. Chirality is the reason you can't shake a person's right hand with your left, or wear your left shoe on your right foot.

Chiral molecules are said to possess "handedness," and in DNA, that handedness is characterized by the direction of its twisting strands. DNA's right-handedness can be identified by a simple trick involving your hands. Take your right hand and, with your thumb pointing upward, imagine grasping the spiral pictured here (in this diagram there is only one helix... in DNA there are two, but this rule still applies). Now imagine your hand twisting around the outside of the spiral, tracing its grooves in the direction that your fingertips are pointing. Your hand should rotate upward along the helix. If you try this trick with your left hand, again grasping the helix with your thumb pointing up, you'll notice that following the rotation of the helix in the direction your fingertips are pointing will cause your hand to move downward.

That means that if you're reading an article online or in a magazine and it features a picture of a left-handed double helix, that picture is wrong, wrong, wrong.

3. Except when it isn't

Yes, most DNA is right-handed. The DNA molecule that Watson and Crick described, for example, was right-handed. But DNA can actually exist in a variety of biologically active helical conformations. The one most people are familiar with is called B-DNA (depicted at center in the image shown here). On the far left is another conformation of DNA, (called A-DNA) that is also right-handed, but more tightly wound than B-DNA. On the far right, however, is a left-handed conformation, known (awesomely) as Z-DNA. So before you go on a pedantic rampage about left- and right-handed DNA, make sure you're not getting all bent out of shape over some Z-DNA (or a plot point in the upcoming Spider-Man movie... watch for the left-handed helices around 1:30).

2. DNA can exist in a variety of bizarre and unfamiliar forms

You want a triple helix? You got it. A transient, four-stranded super-molecule (that just happens to be the lynchpin step in the process of genetic recombination)? Coming right up. How about a smiley face, a map of the Americas, or a nanodrug-carrying box, complete with lock and key? Yeah, we've got those, too. For years, DNA has been growing in popularity as a nano-scale building material for applications in everything from medicine to technology. And we've only just begun to appreciate what these DNA nanomachines are capable of. [DNA tetrahedron via]

1.   We can make synthetic DNA

Strands of DNA and RNA are formed by stringing together long chains of molecules called nucleotides. A nucleotide is made up of three chemical components: a phosphate (labeled here in red), a five-carbon sugar group (labeled here in yellow, this can be either a deoxyribose sugar - which gives us the "D" in DNA - or a ribose sugar - hence the "R" in RNA), and one of five standard bases (adenine, guanine, cytosine, thymine or uracil, labeled in blue).

By swapping out artificial molecules in place of any of these chemical components, researchers can actually make synthetic DNA. One of the most commonly created forms of synthetic DNA is XNA, which swaps out the sugar group for any number of artificially produced molecules. Just last month, researchers succeeded in creating a genetic system that allowed this XNA to replicate and evolve. And to top it all off, this "alien" XNA is actually stronger than the real thing.

Top image and XNA via Shutterstock; all other images via Wikimedia commons unless otherwise indicated

 

From io9 @ http://io9.com/5907275/ten-things-you-probably-didnt-know-about-dna

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