Everything you learned about the shape of DNA is wrong | Hacker News Reader

Everything you learned about the shape of DNA is wrong

statnews.com

18 pointsOsiris307 comments

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-...

"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 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.

> 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-...

https://www.youtube.com/watch?v=TNKWgcFPHqw

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

Here is an explanation of how the hell it does that chemically:

https://www.youtube.com/watch?v=YAva4g3Pk6k

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

https://www.dropbox.com/s/whek2qi8o1yldwk/Screenshot%202016-...

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".

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.

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

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

Not a great start there...

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