Question

In a FRAP experiment using fluorescent antibodies against a cell surface protein, the region of interest that was bleached did not show fluorescence recovery after 30 seconds but did show recovery after 150 seconds. What does this tell you about the mobility of the cell surface protein? (2 points)

Answer 1

First you have to know what is the technique called fluorescence recovery after photobleaching (FRAP)

A component of the cell membrane (in this case the protein) is specifically labeled with a fluorescent chromophore. With a fluorescence microscope a small region of the cell membrane is visualized (even a single protein in the membrane). Fluorescent molecules of this region are destroyed (they are bleached or decolorized) with a very intense pulse of light, coming from a laser. Then the luorescence of this region is controlled, as a function of time, using a sufficiently low luminous level to avoid subsequent bleaching. If the labeled component is mobile, the bleached molecules leave the illuminated region and the unbleached molecules enter it, resulting in an increase in the intensity of the fluorescence.

The rate of recovery depends fluorescence level depends on the lateral mobility of the marked component

This experiment shows that the protein is mobile. To make other assertions regarding this experiment, you need to compare it with other experiments performed. This experiment originally revealed the fluid mosaic model of Singer and Nicolson of cell membranes.