Fluorescence Light Microscopy
The addition of fluorescence to light microscopy allows us to look not just at cells, but for things inside them. Specific cellular components can be fluorescently labeled, with a stain or antibody that binds a particular molecule. Alternatively, a protein of interest can be genetically linked to a fluorescent protein such as Green Fluorescent Protein (GFP, isolated from a bioluminescent jellyfish off the Pacific coast in the 1970s and adapted as a revolutionary molecular biology tool in the 1990s). While tagging a protein can sometimes change its properties (e.g. affecting its function or altering its localization), this technique often enables us to identify where in the cell a protein is found, and what it might be doing there.
As an example, this movie from Howard Berg’s lab   shows Escherichia coli cells stained by a fluorescent dye that binds to and highlights their flagella – long, thin appendages that propel them through their environment. (We will discuss this and other ways cells move in Chapter 6.)