AUTORADIOGRAPHY

AUTORADIOGRAPHY

This is the technique used to observe the distribution of a particular chemical substance in living cells and tissues, and to track the routes and conversions of macromolecules in different biochemical reactions. In autoradiography, radioisotopes (isotopes which can emit ionizing radiations) of some elements (e.g. ^I4C, ³H, ³²P, ³⁵S, etc.) are introduced to the cell. Each of them gets incor­porated with a specific substance and makes it radioactive. This is called la­belling of the substance with radioisotopes, or simply radioactive labelling. Then, the movement and distribution of the labelled substance is observed. This helps to detect the presence of the substance and also to track the syn­thesis of a compound out of it. The radioisotopes can emit one or more of the three radiations, namely alpha and beta particles and gamma rays. Most of the isotopes used in autoradiography are beta-emitters.The cells or tissues, containing radioactively labelled molecules, are placed in contact with a photographic emulsion for a certain period. The ionizing radiations, emitted by the radioisotopes, blacken the emulsion and produces an image, known as autoradiograph. A comparison of this image with the normal cells observed under microscope will enable to detect the location of the radioactive isotope and also to track the route of the radioactively la­belled molecule. Autoradiographs are usually observed with the help of phase contrast microscopes