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Graphical Timeline

The timeline is a chronological depiction of the experiments contained in this module. To use the timeline, click and drag from right to left. You can view individual experiments as they appear by clicking their titles. To scroll more quickly, drag the dark gray strip at the bottom of the window.

You can access a text version of the timeline (that will be more compatible with older browsers) here

  • Modification of DNA using aflatoxin
  • The first step was to make the adduct (if in fact the carcinogenic process stemmed from an adduct; for additional hypotheses, see work by W. Thilly in Nature Genetics), and a method to do this in vitro had previously been worked out in the laboratory by W. Busby. So, most of the experiments in this section are incubations of aflatoxin with DNA and the development of an enzymatic system that formed AFB1*.

  • Liberation of adduct from modified DNA
  • Once the putative adduct had been formed, the next task was to remove it from DNA using hydrolysis methods. A good introduction to this topic is the video Hydrolysis Methods. (Be sure to watch The Early Meeting with George Büchi first.)

  • Isolation of liberated adduct using the extraction approach
  • The next theoretical step is to isolate the adduct from the hydrolysate (the hydrolyzed modified DNA). This short set of experiments attempted using a simple extraction to isolate the adduct.

  • Isolation of liberated adduct using the precolumn approach
  • This alternative to extraction attempted to isolate the adduct using a precolumn. (Good chromatography resources can be found at A working knowledge of the principles underlying chromatographic systems is essential to understand this and the following path.)

  • Isolation of large (mg) quantities of adduct using the preparative column approach
  • Isolating enough adduct to do structural determination was an enormous obstacle. At the time, quantities on the order of milligrams were needed to characterize a structure. A mistake (and the ability to turn it to one's advantage) led to the isolation of a large quantity of pure adduct.

  • Preliminary structure determination
  • Several spectroscopic techniques were used to determine the preliminary structure of the adduct. As with the previous path, a good understanding of spectroscopy is necessary to appreciate fully the work done in deducing the structure. An excellent spectroscopy tutorial can be found at

  • Determination of guanine attachment site to adduct
  • Once the preliminary structure had been formulated, one question remained: on which atom was the guanine attached to the aflatoxin? A beautiful series of experiments yielded a solid answer.

  • Miscellaneous or unknown
  • Publication or presentation
  • The data were in; all that was left was to publish. Was the group quick enough to be the first group with the adduct structure?

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