Microtubules

ID #2290

I don't really understand the concept of the GTP cap, would somebody please elaborate?


Shortly after a tubulin dimer is added to a microtubule, the GTP in the beta subunit is hydrolyzed. The GDP-bound tubulin has a lower affinity for other molecules of tubulin. If there is a lot of free GTP-bound tubulin available near a microtubule, GTP-bound tubulin will be added to the microtubule faster than GTP is hydrolyzed and the microtubule will polymerize (and will have a GTP cap). This basically means that tubulin dimers that have GTP hydrolyzed to GDP are buried inside the microtubule behind more recently incorporated GTP-bound tubulin and so they are "stuck" in the microtubule despite having a lessened affinity for their neighbors. Keep in mind though, that the "GTP cap" is just an arbitrary designation, not a physical capping structure.

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