Inside every cell there are tiny droplets that have no membrane yet work like separate compartments. One of these droplets is made of RNA strands, and at first it looks like liquid jelly: soft, springy, easily changing shape. But over time something changes inside it. The middle becomes solid, like a sponge, while the edges stay liquid. Why this happens was a mystery for a long time. Now scientists have modeled the process on a computer and found the answer.
Each RNA strand with repeating pieces can pair up with neighboring strands. In the middle of the droplet there are more such pairs, because the molecules are crowded there and touch more often. This makes the chains tangle like threads in a ball, and the middle freezes. At the edge there are fewer molecules, they have more room, so the droplet stays liquid there longer. To test how much the order of the letters matters, the scientists made two droplets with the same composition but a different order. The one where the letters were arranged randomly aged several times more slowly.
This discovery helps explain why in some diseases solid clumps of RNA appear in cells. If we learn to keep them from hardening, it may be possible to slow the progress of the disease. For now this is only an idea, but it is now clear what needs to be targeted.
In the core of the droplet, relaxation times are six times longer than at the periphery, and the density of entanglement nodes is five times higher. Yet both sequences have the same nucleotide composition but a different order, and that alone is enough for one to age five times faster than the other.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.