Sunday, November 11, 2012

Brushing my biology: cool diagram of chromosomes in the nucleus

I already mentioned this ENCODE discuthon we have next week. As I have to discuss stuff about hypersensitive DNA regions, I have to seriously brush up my biology. Brush up?? That suggests there was a decent basis. Well, think again. I though history was much more interesting!

I am a chemist. When people talk about the DNA in the cell, I always considered a single molecule. Until I learned there are 46 chromosomes. So, each cell actually has 92 DNA molecules. That was a revelation I had somewhere in my second or third year at the university. Remember, I did not have biology in secondary school.

Anyway, no book ever showed me what that really looks like. Yeah, schema. Cell diagrams with one mitochondrion in the cell. Well, bloody yes, the cell has very many of them, thank you very much. It just did not fit the diagram, I guess...

So, I just ran into this way cool figure from the Three-Dimensional Maps of All Chromosomes in Human Male Fibroblast Nuclei and Prometaphase Rosettes paper by Bolzer et al. (doi:10.1371/journal.pbio.0030157). I actually ran into the WikiPedia version of it, in the chromosome article. It's an adaption, but the original is much better even.

I can just wish they had added a Jmol applet with the 3D rods, rather than these static images.

But I find the flatness at 90o weird... what is the story behind that? Is their method not really or not fully 3D? I guess I will have to find some time to read up on their Methods section...


  1. There is some great work using electron cryo-microscopy to capture 3D views of cell components, e.g. large protein complexes in situ. See e.g. the Baumeister group:

    (and a correction; only 2 x 23 = 46 chromosomes per diploid human cell, not 2 x 46).

    1. Each DNA chromosome is a double helix consisting of two individual DNA strands/molecules ?

    2. I don't know that most people would call each strand of the helix a separate molecule, since chromosomes are capped at each end and so the strands are connected. Interesting idea though, from a chemist perspective that a biologist would not think of!

      And when I think about it: there is also mitochondrial DNA and there may be many mitochondria per cell, so there are more than 92 molecules per cell in any case.

    3. +1

      I was not aware of that capping! Never seen that! Do you have a pointer for that?