Actin filament construction set
by destroyer2012, published
This is a protein model that can be assembled (polymerized) in an analogy to what happens inside living cells.
Actin is a protein involved in maintaining a cell's shape, as part of what's called the cytoskeleton. Actin exists as monomers, but certain conditions (like the actions other proteins, or the presence of certain salts) cause the monomers to stick together and create these long, helical filaments.
Read more about actin here http://www.rcsb.org/pdb/101/motm.do?momID=19
Print with support. I used KISSlicer, printing at 0.16 layer height at 0.45 extrusion width, scaling down the support flow rate to 75%. The model is supposed to be elevated from the platform, this helps the first layers form properly. If you don't use a heated platform you can print the non-elevated version.
Print many monomers and then put them together to make a filament! You'll need at least three before the filament structure becomes stable (Just like the real thing!) and then it's easier to add more to the plus end than the minus end (also realistic).
EDIT (9/20/2013) There seems to be some confusion as to the orientation you should print the monomer in. I have tried many other orientations and this one is the best in terms of strength, surface quality, and support effectiveness. Do not rotate it or you will get a worse model.