Is DNA actually a double helix? Why no google image results?

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Is DNA actually a double helix? Why no google image results?

Postby .Salo. » Thu Mar 18, 2010 5:02 pm UTC

I keep seeing computer models and drawing, and once a back tattoo, but no pictures of the real thing. I remember the story of Francis Crick. I think? His discovery of the double helix took place in his imagination. This makes me wonder if the discovery of the double helix was actually the discovery of how to conceptualize, and thus solve, or work with, the puzzle which is DNA. I've seen the pictures of a nucleus and X shaped DNA. It looked like two double helixes crossed, but if I hadn't heard of a double helix before, I'd say it looked like two crossed rods instead. Do we have any photographs of the actual double helix?

I'd just like to see the bastard that's so hell bent on making more of itself for no good reason at all. Or is there a good reason? Compete for survival, why? The purpose of life on this planet surely can't be to devour everything, can it? Perhaps intelligence is a necessary part of evolution so a species doesn't destroying itself through it's own success; After it's conquered the planet. Can we get smart enough to save ourselves from destroying this rock?

Carl Sagan's "Cosmos" has that affect (effect?) on me. ^^^

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Re: Is DNA actually a double helix? Why no google image resu

Postby gmalivuk » Thu Mar 18, 2010 5:11 pm UTC

There is no purpose of life, whether to devour everything or live in harmony with everything or anything in between.

And the double helix was iirc discovered through X-Ray crystallography, so the famous picture is along the axis rather than from the side, and you have to know what you're looking at to conclude that it's a double helix.
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Re: Is DNA actually a double helix? Why no google image resu

Postby Izawwlgood » Thu Mar 18, 2010 5:29 pm UTC

I'm curious why you would find a computer model somehow insufficient proof that it is a double helix. The basic layout is known, lots of organic chemistry has been done to prove that it fits the way we know it does; it's like not trusting that benzene is a six carbon ring with resonance because you've never seen it.
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Re: Is DNA actually a double helix? Why no google image resu

Postby bigglesworth » Thu Mar 18, 2010 5:34 pm UTC

This might help:
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Re: Is DNA actually a double helix? Why no google image resu

Postby drosophila » Thu Mar 18, 2010 5:51 pm UTC

gmalivuk wrote:And the double helix was iirc discovered through X-Ray crystallography, so the famous picture is along the axis rather than from the side, and you have to know what you're looking at to conclude that it's a double helix.

That picture is not a picture of DNA along the axis or otherwise. That is a diffraction pattern that is formed when you shoot a crystal or a fiber with X-rays. In crystal diffraction, which has been done to determine the structure of DNA, the pattern of spots that shows up on the detector is directly related to the molecule's electron density (and thus it's "shape") via a Fourier transform, but is not actually a picture of the molecule itself. The famous plate that gmalivuk linked to was done by fiber diffraction, which I'm not real familiar with, but I've read that the "X" you can see in the middle of the image is indicative of a helix (while not actually being an image of a helix).

To the OP, it's not actually possible to take a photograph of DNA directly. It's too small for visible light waves to resolve it. So, we have to collect X-ray data and then use it to build a 3D model of the molecule. That said, X-ray diffraction produces strong data, that is in no way less certain than a photograph or micrograph.

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Re: Is DNA actually a double helix? Why no google image resu

Postby Qaanol » Thu Mar 18, 2010 6:12 pm UTC

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Re: Is DNA actually a double helix? Why no google image resu

Postby Izawwlgood » Thu Mar 18, 2010 6:13 pm UTC

Oh?
And yes, I know it's not light microscopy. That was more in response to the 'you can't take pictures of DNA directly' comment.
Last edited by Izawwlgood on Thu Mar 18, 2010 6:13 pm UTC, edited 1 time in total.
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Re: Is DNA actually a double helix? Why no google image resu

Postby .Salo. » Thu Mar 18, 2010 6:13 pm UTC

Izawwlgood wrote:I'm curious why you would find a computer model somehow insufficient proof that it is a double helix. The basic layout is known, lots of organic chemistry has been done to prove that it fits the way we know it does; it's like not trusting that benzene is a six carbon ring with resonance because you've never seen it.


Well, I definitely thought there was a possibility that the double helix wasn't actually what the stuff looked like. That the discovery was a flash of insight into a problem. A different way of dealing with it by arranging it as a double helix.
However, there was zero doubt in my mind that DNA is what we say it is and that it works how we say it works. I just suspected it was possible that the discovery wasn't proof that DNA was physically a double helix, but that it should be thought of as a double helix. It's almost the same thing, I admit.
It's possible for something to be understood and never seen. I was wondering if DNA was in that category.
I suspected this because in the age of nanotechnology, I haven't seen one picture of an actual double helix. I thought that maybe the stuff was too small, or too convoluted to be proven to be a double helix. But I thought it must be similar because thinking of it as a double helix makes it understood.

My only doubt was placed on the sophistication of our scientific instruments. It's been a while since the famous image gmalivuk graciously provided was taken. I understand there is no need to take another one, but if we have better equipment than why not. I need a new desktop background.

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Re: Is DNA actually a double helix? Why no google image resu

Postby Charlie! » Thu Mar 18, 2010 6:59 pm UTC

.Salo. wrote:
Izawwlgood wrote:I'm curious why you would find a computer model somehow insufficient proof that it is a double helix. The basic layout is known, lots of organic chemistry has been done to prove that it fits the way we know it does; it's like not trusting that benzene is a six carbon ring with resonance because you've never seen it.


Well, I definitely thought there was a possibility that the double helix wasn't actually what the stuff looked like. That the discovery was a flash of insight into a problem. A different way of dealing with it by arranging it as a double helix.
However, there was zero doubt in my mind that DNA is what we say it is and that it works how we say it works. I just suspected it was possible that the discovery wasn't proof that DNA was physically a double helix, but that it should be thought of as a double helix. It's almost the same thing, I admit.
It's possible for something to be understood and never seen. I was wondering if DNA was in that category.
I suspected this because in the age of nanotechnology, I haven't seen one picture of an actual double helix. I thought that maybe the stuff was too small, or too convoluted to be proven to be a double helix. But I thought it must be similar because thinking of it as a double helix makes it understood.

My only doubt was placed on the sophistication of our scientific instruments. It's been a while since the famous image gmalivuk graciously provided was taken. I understand there is no need to take another one, but if we have better equipment than why not. I need a new desktop background.

One trick is that if it's only "understood as a double helix", the binding energies don't work. It has to actually be a double helix, even with just the information available to Watson and Crick. You shouldn't focus on "seeing" too much; the other senses are also quite real.
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Re: Is DNA actually a double helix? Why no google image resu

Postby Izawwlgood » Thu Mar 18, 2010 7:11 pm UTC

Yeah. Like I said, we know what benzene molecules look like without having 'seen' them. Recently, someone imaged a naphalene molecule (I think?) and 'lo! it looks exactly like we thought it did. The sophistication of instrumentation provides clues, our knowledge of chemical interactions provides other clues, and various other neat tricks provide more clues. We don't need to 'see' something to be able to elucidate it's structure.
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Re: Is DNA actually a double helix? Why no google image resu

Postby TescoPeeledPlums » Thu Mar 18, 2010 7:20 pm UTC

Izawwlgood wrote:Yeah. Like I said, we know what benzene molecules look like without having 'seen' them. Recently, someone imaged a naphalene molecule (I think?) and 'lo! it looks exactly like we thought it did. The sophistication of instrumentation provides clues, our knowledge of chemical interactions provides other clues, and various other neat tricks provide more clues. We don't need to 'see' something to be able to elucidate it's structure.


See the folding@home protein folding project to see when things are too hard to image and work out from the standard rules we have, and when computer networking comes into its own.
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Re: Is DNA actually a double helix? Why no google image resu

Postby drosophila » Thu Mar 18, 2010 7:34 pm UTC

.Salo. wrote:My only doubt was placed on the sophistication of our scientific instruments. It's been a while since the famous image gmalivuk graciously provided was taken. I understand there is no need to take another one, but if we have better equipment than why not. I need a new desktop background.


There has been tons of crystallography of DNA since Franklin's original work, all producing the same structure. People still solve DNA structures to understand how DNA-based chemical and biological processes are regulated. Furthermore, some people look at DNA's structure using solution NMR which is a relatively novel technique compared to structure by crystallography, and they also see the double helix.

@Izawwlgood: Ha ha, good point, I guess what I was really trying to say is that the details of the DNA double helix can't be resolved by microscopy. :P

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Re: Is DNA actually a double helix? Why no google image resu

Postby psychosomaticism » Thu Mar 18, 2010 7:55 pm UTC

Electron Microscopy has also come a long way:
Image

I think the original question is a bit misplaced, as I understood this:
I've seen the pictures of a nucleus and X shaped DNA. It looked like two double helixes crossed, but if I hadn't heard of a double helix before, I'd say it looked like two crossed rods instead.

to mean that the two homologous chromatids of dna are just helices themselves, whereas they are made of a whole lot of supercoiled and scaffolded helices, as in this picture:
Image

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Re: Is DNA actually a double helix? Why no google image resu

Postby Qaanol » Thu Mar 18, 2010 8:06 pm UTC

In addition to the links in my earlier post and the above post, if you want a desktop background perhaps you could seek permission from the author to use this image.
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Re: Is DNA actually a double helix? Why no google image resu

Postby Izawwlgood » Thu Mar 18, 2010 8:09 pm UTC

Is that you? Neat image.
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Re: Is DNA actually a double helix? Why no google image resu

Postby Qaanol » Thu Mar 18, 2010 9:16 pm UTC

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Re: Is DNA actually a double helix? Why no google image resu

Postby Omegaton » Thu Mar 18, 2010 9:39 pm UTC

Izawwlgood wrote:Yeah. Like I said, we know what benzene molecules look like without having 'seen' them. Recently, someone imaged a naphalene molecule (I think?) and 'lo! it looks exactly like we thought it did. The sophistication of instrumentation provides clues, our knowledge of chemical interactions provides other clues, and various other neat tricks provide more clues. We don't need to 'see' something to be able to elucidate it's structure.

Off topic, but it was pentacene. The pic is even on Wikipedia now: http://en.wikipedia.org/wiki/Pentacene

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Re: Is DNA actually a double helix? Why no google image resu

Postby .Salo. » Fri Mar 19, 2010 12:23 am UTC

psychosomaticism wrote:to mean that the two homologous chromatids of dna are just helices themselves, whereas they are made of a whole lot of supercoiled and scaffolded helices, as in this picture:
Image


My misconception about the "X" shaped DNA is clarified. Thanks!

TescoPeeledPlums wrote:See the folding@home protein folding project to see when things are too hard to image and work out from the standard rules we have, and when computer networking comes into its own.


I saw something very similar to this on the news last year. But it looked nothing like the folding@home project. I'll have to figure out what that was now.

Qaanol wrote:This might help.


"This" was very helpful. "might" was very interesting. "help" was unfair. I didn't know what a scanning tunnelling microscope was. But good times though.

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Re: Is DNA actually a double helix? Why no google image resu

Postby screen317 » Sun Feb 12, 2012 11:26 pm UTC

I was reading through our Science Forum archives, and I wanted to post this image (didn't want to start a new thread about this topic since this thread is pretty comprehensive already):

http://www.physorg.com/news4616.html


Atomic Force microscopy is taking off at UCLA where I currently do research. It's rather exciting.

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Re: Is DNA actually a double helix? Why no google image resu

Postby Izawwlgood » Mon Feb 13, 2012 1:38 am UTC

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Re: Is DNA actually a double helix? Why no google image resu

Postby Angua » Mon Feb 13, 2012 8:36 am UTC

DNA being a double helix also works when you think about how you need enzymes to separate and unwind the strands, plus one that has to nick a strand every so often so the strain from the unwinding that you get during replication doesn't destroy the whole thing.

(Too early in the morning for names of enzymes).
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Re: Is DNA actually a double helix? Why no google image resu

Postby Gigano » Sat Feb 18, 2012 11:48 am UTC

Angua wrote:DNA being a double helix also works when you think about how you need enzymes to separate and unwind the strands, plus one that has to nick a strand every so often so the strain from the unwinding that you get during replication doesn't destroy the whole thing.

(Too early in the morning for names of enzymes).


Topoisomerase types I and II.

Another aspect that helps to convince that DNA actually is a double helix is the behaviour of circular DNA, plasmids. Because of the helical structure, a plasmid tends to curl itself as a result of the 'stress' the molecule undergoes. This results in so called coiled and supercoiled structures, which be seen here. This conformation by the way alters the rate at which the molecule can move through an agarose gel during gel electrophoresis, which is often used to separate DNA fragments of different sizes. A non-linear circular DNA molecule is more compact than a linear fragment of the same size in terms of base pairs. This allows the fragment to move faster through a gel than its linear variant. An open nicked piece of DNA has only a single strand break, causing the plasmid to unwind into a fully relaxed state and decreasing the mobility of the molecule.

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