Question

When the concentration of GTP-bound tubulin is low, what happens?

1) The microtubule shrinks in length.
2) It shows affinity for actin instead of microtubules.
3) ATP can now bind tubulin instead.
4) It has a great affinity for the minus end of the microtubule.
5) The microtubule grows in length.

Answer 1

When the concentration of GTP-bound tubulin is low, the microtubules will shrink in length due to the lack of GTP-charged tubulin necessary for their elongation; the correct answer, therefore, is that the microtubule shrinks in length. The correct answer is option 1.

Step-by-step explanation:

When the concentration of GTP-bound tubulin is low, it indicates that the tubulin dimers are not adequately charged with GTP to support the polymerization process necessary for the elongation of microtubules.

As a result, the microtubules are unable to sustain their growth, and instead, they begin to shrink as dimers are lost from their plus ends. This process is known as depolymerization or catastrophe. GTP binding provides the energy for tubulin to add to the growing microtubule, and a low GTP-tubulin concentration means there is less substrate to add to the plus end of the microtubules, delaying polymerization and favoring disassembly.

Therefore, the correct answer to when the concentration of GTP-bound tubulin is low is: 1) The microtubule shrinks in length.