
Everything you learned about the shape of DNA is wrong - Osiris30
https://www.statnews.com/2016/03/31/dna-shape-double-helix-dekker/
======
Jun8
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-...](http://wow-
really.blogspot.com/2006/11/your-dna-would-reach-moon.html)

"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
> 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-...](http://www.hhmi.org/biointeractive/dna-replication-advanced-
detail)

[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
The closed captions on that last video are pretty a-ok:

[https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-...](https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-03-31%2017.21.35.png?dl=0)

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castratikron
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".

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dekhn
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
That title is so egregious that rather than trying to fix it we just flagged
the post.

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glwtta
"We each have about 20,000 genes, all of which sit together on a molecule of
DNA."

Not a great start there...

