Autoradiography animation

To the right is an animation which illustrates the results which would be produced by an autoradiography experiment wherein cells (eukaryotic) growing in culture are first fed radioactive amino acids (the pulse) and then non-radioactive amino acids (the chase). At various times, representative cells are withdrawn, fixed, stained for electron microscopy, covered with autoradiography emulsion and allowed to radioactively expose the emulsion. Once the emulsion is exposed, the emulsion is developed and the cells are observed by electron microscopy. The electron microscopy allowed the observation of fixed and stained cellular components as well as the location of the radioactivity as green dots. The location of the radioactivity in the cell changes with time.

The animation shows that when one observes the location of the radioactivity very shortly after administering the radioactive amino acids, most the radioactivity is found associated with the RER where new proteins are being actively synthesized from the radioactive amino acids. These radioactive proteins become either integral proteins of the RER membrane or hydrophilic proteins sequestered in the lumen of the RER.

A little later, after the administration of the non-radioactive amino acids, new protein synthesis is all with the non-radioactive amino acids and the proteins synthesized with the non-radioactive amino acids are therefore invisible. However, the proteins which were synthesized using the radioactive amino acids are still radioactive and are therefore still visible. These radioactive proteins have now moved from the RER to the SER.

After a little more time, the radioactive proteins leave the SER and move into the vesicles which coelesce to form the Golgi apparatus. The radioactive proteins move sequentially through the lamellae of the Golgi and then into the secretion vesicles. The secretion vesicles carrying the radioactive proteins flow outward and eventually fuse with the plasma membrane (PM) dumping their soluble contents outside of the cell. As the secretion vesicles fuse with the PM, the membrane of the secretion vesicle becomes the PM. Thus, the radioactive proteins once synthesized in the RER and incorporated into the the RER membrane have "flowed" outward and eventually become part of the PM of the cell.