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

In addition to their structural support role, microtubules also serve as a highway system along which organelles can be transported with the aid of motor proteins. For instance, the microtubule network interconnects the Golgi apparatus with the plasma membrane to guide secretory vesicles for export, and also transports mitochondria back and forth in the cytoplasm. Another example is the translocation of vesicles containing neurotransmitters by microtubules to the tips of nerve cell axons. The motor proteins involved in organelle transport operate by altering their three-dimensional conformation using adenosine triphosphate (ATP) as fuel to move back and forth along a microtubule. With each step, the motor molecule releases one portion of the microtubule and grips a second site farther long the filament. Motor proteins, which are grouped into several distinct classes, attach to organelles through specialized receptors. The digital video in this section illustrates the interplay between mitochondria (labeled with DsRed fluorescent protein) and the microtubules by examining the tracking of microtubule +TIPs (plus end tracking proteins) labeled with EB3 fused to mEGFP.