How to model a nucleosome fiber

Apologies in advance for a simple question from a new user.

I’m a scientist that does work on nucleosome fibers. I would like to create a blender model of a nucleosome fiber to which I will eventually add bones so I can easily manipulate and animate. It is basically long tube wrapped around a fat cylinder. The model will use a cylindrical tube for the DNA and a fat cylinder for the protein core. I’ve tried a couple of simple steps (using twist on a circle, etc), but I’ve had little luck. The details of the model (translating 1 blender unit=1 nm) are that the protein cylinder (the easy part) will be 10x6 in size and the DNA tube (minor radius of 1) should wrap around the cylinder 1.65 times.

I’m sure I can do it all by hand with extrusions, but I’d like to be a bit more precise and add some constraints to the DNA as it exits the nucleosome (should not bend in an arc of a radius of 8 units or less).

I’ve included a picture of the fiber in the post (as a new user I can’t post a link), but if you look on wikipedia for nucleosome, you can grab a high resolution picture.

Thanks for any help! I’m loving this program so far.

Although this doesn’t have the desired automatic control over radii, simply modeling what you want with curves might work. You could always write a python program with the precise locations of the nucleosome parts, but this might provide an easier start for you: (86.9 KB)

Thanks! This looks great! It’s actually even more detailed than I had planned (the part you have as a helix I was just going to model as a tube). Even if I decide to go a different route, the trick with the curves and the array modifier is going to be incredibly useful in the future.

I assume it’s pretty trivial to add armature to this for easy manipulation/IK constraints? I’ve found some tutorials on adding armature to curves that I was going to follow.

I have a soft spot for scientific visualization. The blend file above is set up for using shape keys to animate the curve. Pretty straight forward, but tedious for keeping the protein cylinders in the right places if you do a lot of these. You can add an armature and constraints to a curve, however I’m not sure you can get the helix array to follow it when you move to new positions. Rather than using a modifier to make your helix array follow a curve, just make a long helix mesh (you’ll probably have to apply the array modifier for some fixed length/number), then parent the mesh to an armature composed of a lot of bones. Other forum members will be much better than I at helping with armatures. That’s a lot to learn, but your results will be probably look great!

P.S. Here’s an example of a short animation using a single shape key with the curve and moving the protein with key frames. For comparison sake I rendered it with Blender Internal and freestyle instead of cycles.