Objective: UPlanSApo 100x oil/1.40	Exposure: 250 ms
Microscope: Olympus DSU/IX81	Gain: 3
Camera: Hamamatsu ImagEM	Interval: 500 ms

The ends of microtubules are always in dynamic formation in that the addition or removal of tubulin proteins is continuously altering the length of the polymer. The rate of depolymerization is different for each end according to its polarity, and the side that grows the fastest is considered the positive end while the other, more stable end, is considered negative. The dynamic, fast-growing portion of the microtubule is composed of beta-tubulin projected out toward the surface of the cell. The alpha-tubulins stabilize their structure toward the nucleus at the centriole located in the centrosome of the cell. Tubulin is transported around the cell by the very microtubules they modify when and where restructuring is needed. The digital video above illustrates the tracking of microtubule +TIPs (plus end tracking proteins) in human cervical carcinoma (HeLa line) epithelial cells labeled with a chimera of EB3 fused to mEGFP.