Autoradiography is used through the use of electron microscopes.
1. Allows bacterium to absorb 3H-Thymidine (Tritiated thymidine)
-contains tritium, a radioactive isotope of hydrogen, so radioactively labelled DNA was produced by replication in the E. coli cells.
2. Cells were then placed onto a dialysis membrane and their cell walls were digested using the enzyme lysozyme.
-cells were gently burst to release their DNA onto the surface of the dialysis membrane.
3. A thin film o photographic emulsion was applied to the surface o the membrane
-being left in darkness for weeks
-some o the atoms o tritium in the DNA decayed and emitted high energy electrons, which react with the film.
-each point where a tritium atom decayed there is a dark grain.
The film showed that prokaryotic chromosomes are circular, and the length and width of the chromosomes can be determined.
-chromosome in E. coli is a single circular DNA molecule with a length o 1,100 microm. (the E coli cells is only 2 microm!)
-prokaryotic chromosomes are circular
-measured the lengths of chromosomes.
-he also observed the DNA replication fork.