An example of an intricate three-dimensional shape taken by RNA is the ribosome. Although it is more than just RNA, a large part of its structure is made of it. There are other structural and functional proteins involved, but it’s interesting to think about. The ribosome reads mRNA, a more specialized RNA molecule, and translates it to an amino acid chain.
This idea relates back to the difference in hydrogen bonding between nucleotide pairs. Because the AT pair has only two hydrogen bonds and CG has three, it requires more energy to break apart a strand of DNA that has a majority of CG pairs. Thus, it requires more heat to denature DNA of this nature and less heat to denature a majority AT strand of DNA.
I know that the interior of the microtubule is not believed to have serve a function, but I just think that its strange that it's entirely hollow. Just based on the tubulin composition, I would assume that there is some type of electrostatic interaction that exists on the interior of the microtubule, like hydrogen bonds of ionic interactions. Another idea is that perhaps the reagents needed for GTP hydrolysis of the microtubule are able to flow through in interior and increase the rate, affecting dynamic instability. Of course, it could just be as simple as we suspect.