The life of microtubules

If you'd like to read something like a "funny" paper about microtubules, look at "Dynamic instability 30 years later: complexities in microtubule growth and catastrophe" by G. J. Brouhard, which was published in Molecular Biology of the Cell in 2015. There's a diagram of microtubules wearing diapers, then head phones, then a tie, finally carrying crutches before the "catastrophe" comes. When I saw the scheme, I thought I had not slept enough or somebody put something for experimental purposes into my tea.

But it's still there and it's supposed to visualize the growth of microtubules from "babies" to "adults" until they become "old" and stop growing before the catastrophe, the shrinking event, begins. So imagine something is growing, i.e. there is always stuff added and suddenly it stops doing so and falls apart. But, why? If you're lucky, the microtubule might not completely shrink away as there could be a "rescue" event where the microtubule starts growing again! How and why this is exactly happening is even more complicated.

The tip of microtubules contains GTP, which builds a stable complex with the protein that microtubules are made of (tubulin). Later on, GTP is turned into GDP, which makes the microtubule less stable. Thus, the GTP tip seems to hold the microtubule end together (because everything behind the tip contains GDP which is less stable and would make the microtubule fall apart!). The GTP tip becomes smaller, but when more tubulin is added, the tip grows again. The switch from growing to stagnating to shrinking microtubules seems to happen when the GTP tip vanishes and the "instable" GDP-tubulin is the new tip and make the microtubule falls apart. 

So, if the tip is longer, then the microtubule would vanish less easily? Well, no. The probability that the microtubule falls apart depends on it's age / length, so there must be something like a microtubule memory, or maybe it's the accumulation of defects (when tubulin does not stick together in the perfect order it's supposed to)?
It's kind of a simple system if you just look briefly at it, but there's lots of research to be done about it.