Question

You add a fluorescent antibody to a cell surface protein to a dish of cells. Looking at an individual cell under the microscope the entire surface of the cell is fluorescent. You then hit the cell with a brief pulse from a laser which bleaches out part of the fluorescence on the cell. Over time you notice that the entire surface of the cell becomes fluorescent again. What is the best explanation for this observation?

1. Proteins from parts of the cell membrane that were not bleached with the laser diffuse into regions of the membrane that were bleached.

2. The fluorescent antibodies are taken up by diffusion.

3. New fluorescent proteins are made by the cell.

4. The antibodies fall off of the proteins in the cell.

Answer 1

The best explanation for this observation is-

1-  Proteins from parts of the cell membrane that were not bleached with the laser diffuse into regions of the membrane that were bleached.

This is because initially the entire surface of the cell is fluorescent and when a brief pulse from laser hits on the cells, it bleaches out the part of the fluorescent on the cell.

Since the bleached part gets recovered by the fluorescent proteins, this phenomenon is called FRAP which is fluorescence recovery after photobleaching. It is a method for determining the kinetics of diffusion through tissue or cells.