Abstract
Specific subsets of biochemical reactions in eukaryotic cells are restricted to individual membrane compartments, or organelles. Cells, therefore, face the monumental task of moving the products of those reactions between individual organelles. Because of the high density of the cytoplasm and the large size of membrane organelles, simple diffusion is grossly insufficient for this task. Proper trafficking between membrane organelles thus relies on cytoskeletal elements and the activity of motor proteins, that act both in transport of membrane compartments and as tethering agents to ensure their proper distribution and to facilitate organelle interactions.