Antibody labeling of proteins like that used in immune-fluorescence analysis can be applied to electron microscopy, but instead of using fluorescent labels attached to antibodies, investigators use gold particles that are electron dense and appear as uniform dots in an electron micrograph. Furthermore, by varying the size of the gold particles (e.g., 5 nm vs 10 nm), one can identify the localization of more than one protein in the cell.

a. Using this approach, investigators have determined the subcellular localization of Tim and Tom proteins used for protein import into mitochondria. In the drawing of the results below, label the gold particles showing the localization of Tim44 and Tom40. What made you come to these conclusions?