For nearly 300 years, cell biology has been largely an observational science. Robert Hooke in 1665 saw structures under the microscope that he called cells. Anthony van Leeuwenhoek discovered cellular substructures in 1700, which Robert Brown dubbed 'nuclei' in 1833. Cell biologists have described many other substructures since then, the most prominent among them being the mitochondria, Golgi apparatus, endoplasmic reticulum, and nucleolus.
With the advent of molecular biology, cell biologists were no longer content to observe these structures' shapes; they wanted to identify their molecular components and learn how those components govern organellar function. In so doing, they could fulfill two interrelated goals. The first, identifying a protein's location or cellular home, helps us to understand how particular organelles work. At the same time, because each organelle has unique functions, assigning novel proteins to a specific cellular address offers vital clues to determining those molecules' duties.
For years, as ...
