3 ms·

Everything you learned about the shape of DNA is wrong

18 points by Osiris30 11y ago

dekhn 11y ago
clickbait headline. Most people learn about the abstract double helix structure that is a rigid rod, but that's still quite applicable and correct for many situations. What this article is really about is that DNA folds into complex 3D structures; most of this was actually known in the 80s and 90s and very little additional work has been done, much to my chagrin.
- dang 11y ago
  That title is so egregious that rather than trying to fix it we just flagged the post.
castratikron 11y ago
You could stand to turn down the hyperbole in the title. I knew that DNA was a double helix, and apparently that isn't "wrong".
glwtta 11y ago
"We each have about 20,000 genes, all of which sit together on a molecule of DNA." Not a great start there...
Jun8 11y ago
The money sentence is: "Each DNA molecule is six feet long. Our cells have to wind it tightly to fit in their interior — without tangling them in knots in the process. In fact, our cells have to unfold and refold DNA in order to read their genes." Holy crap! This sounds so unbelievable at first sight that I googled it: From http://wow-really.blogspot.com/2006/11/your-dna-would-reach-moon.html http://wow-really.blogspot.com/2006/11/your-dna-would-reach-... "The human genome, the genetic code in each human cell, contains 23 DNA molecules each containing from 500 thousand to 2.5 million nucleotide pairs. DNA molecules of this size are 1.7 to 8.5 cm long when uncoiled, or about 5 cm on average." So 23*8.5cm ~ 2m. From https://en.wikipedia.org/wiki/Cell_nucleus https://en.wikipedia.org/wiki/Cell_nucleus we learn that the average size of a nucleus is 6 micrometers. if we just folded the total DNA like rope, halving it at each turn we need about 19 folds, which is huge! It would be interesting to calculate to see if a structure like the 3D Hilbert curve has enough packing efficiency to fit a strand this long into the nucleus.
- tzs 11y ago
  > Holy crap! This sounds so unbelievable at first sight that I googled it That's nothing. If you want to see something even more unbelievable, look at what happens when it is unfolded for replication: http://www.hhmi.org/biointeractive/dna-replication-advanced-detail http://www.hhmi.org/biointeractive/dna-replication-advanced-... https://www.youtube.com/watch?v=TNKWgcFPHqw https://www.youtube.com/watch?v=TNKWgcFPHqw https://www.youtube.com/watch?v=JZXT2uOcD2w https://www.youtube.com/watch?v=JZXT2uOcD2w There is some pretty amazing stuff going on in the cell outside the DNA, too. To move stuff through the cell there are a series of things called microtubule. Think of them as like catwalks connecting various regions. To move things through the cell things called "motor proteins" are used. These are long proteins that attach at one end to thing to be moved, and (I'm not kidding) have a couple little feet at the other end that they use to walk along the microtubule towing their cargo. Here's an animation of one walking: https://www.youtube.com/watch?v=xlPDEpimzB8 https://www.youtube.com/watch?v=xlPDEpimzB8 Here is an explanation of how the hell it does that chemically: https://www.youtube.com/watch?v=YAva4g3Pk6k https://www.youtube.com/watch?v=YAva4g3Pk6k
  - tptacek 11y ago
    The closed captions on that last video are pretty a-ok: https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-03-31%2017.21.35.png?dl=0 https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-...

18 points by Osiris30 11y ago

dekhn 11y ago

clickbait headline. Most people learn about the abstract double helix structure that is a rigid rod, but that's still quite applicable and correct for many situations. What this article is really about is that DNA folds into complex 3D structures; most of this was actually known in the 80s and 90s and very little additional work has been done, much to my chagrin.

dang 11y ago
That title is so egregious that rather than trying to fix it we just flagged the post.

castratikron 11y ago

You could stand to turn down the hyperbole in the title. I knew that DNA was a double helix, and apparently that isn't "wrong".

glwtta 11y ago

"We each have about 20,000 genes, all of which sit together on a molecule of DNA." Not a great start there...

Jun8 11y ago

The money sentence is: "Each DNA molecule is six feet long. Our cells have to wind it tightly to fit in their interior — without tangling them in knots in the process. In fact, our cells have to unfold and refold DNA in order to read their genes." Holy crap! This sounds so unbelievable at first sight that I googled it: From http://wow-really.blogspot.com/2006/11/your-dna-would-reach-moon.html http://wow-really.blogspot.com/2006/11/your-dna-would-reach-... "The human genome, the genetic code in each human cell, contains 23 DNA molecules each containing from 500 thousand to 2.5 million nucleotide pairs. DNA molecules of this size are 1.7 to 8.5 cm long when uncoiled, or about 5 cm on average." So 23*8.5cm ~ 2m. From https://en.wikipedia.org/wiki/Cell_nucleus https://en.wikipedia.org/wiki/Cell_nucleus we learn that the average size of a nucleus is 6 micrometers. if we just folded the total DNA like rope, halving it at each turn we need about 19 folds, which is huge! It would be interesting to calculate to see if a structure like the 3D Hilbert curve has enough packing efficiency to fit a strand this long into the nucleus.

tzs 11y ago
> Holy crap! This sounds so unbelievable at first sight that I googled it That's nothing. If you want to see something even more unbelievable, look at what happens when it is unfolded for replication: http://www.hhmi.org/biointeractive/dna-replication-advanced-detail http://www.hhmi.org/biointeractive/dna-replication-advanced-... https://www.youtube.com/watch?v=TNKWgcFPHqw https://www.youtube.com/watch?v=TNKWgcFPHqw https://www.youtube.com/watch?v=JZXT2uOcD2w https://www.youtube.com/watch?v=JZXT2uOcD2w There is some pretty amazing stuff going on in the cell outside the DNA, too. To move stuff through the cell there are a series of things called microtubule. Think of them as like catwalks connecting various regions. To move things through the cell things called "motor proteins" are used. These are long proteins that attach at one end to thing to be moved, and (I'm not kidding) have a couple little feet at the other end that they use to walk along the microtubule towing their cargo. Here's an animation of one walking: https://www.youtube.com/watch?v=xlPDEpimzB8 https://www.youtube.com/watch?v=xlPDEpimzB8 Here is an explanation of how the hell it does that chemically: https://www.youtube.com/watch?v=YAva4g3Pk6k https://www.youtube.com/watch?v=YAva4g3Pk6k
- tptacek 11y ago
  The closed captions on that last video are pretty a-ok: https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-03-31%2017.21.35.png?dl=0 https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-...