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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 p
by 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 agoThe 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-...