PACIFIC SOUTHWEST ASSOCIATION O F CHEMISTRY TEACHERS MEETING OF THE NORTHERN SECTION
Tm Pacific Southwest Association of Chemistry Teachers, Northern Section, met late in April fora twoday session in San Francisco. I n addition to carrying on the business of the society, members of the Association were privileged to hear interesting lectures by B. M. Tolbert on the use of radioactive tracers and George Gamow on a new theory of the function of the chromosomes in guiding cell replication. On the afternoon of the second day the members met jointly with the science fair sponsored by the National Association of Manufacturers. Dr. Tolbert, a research chemist a t the University of California radiation laboratory in Berkeley, referred to radioactive tracers as tools with which to work on problems in biochemistry. Confining his attention to C14, he showed first how this isotope could be introduced into a molecule of a drug such as codeine, and then how the disposition of the radioactive element could be traced in the human body. According to Tolbert's figures, whereas 90 per cent of the radiocarbon from his specially prepared glycine appears in the breath, only 10 per cent of the radioactive carbon in the drug Demerol is so excreted. From other drugs the radioactive element may appear largely in the urine; with still others most of the C14 goes into the feces. Describing an interesting development of these experiments, Tolbert showed a slide of an ingenious apparatus used to make a continuous record of the C14 content in the breath of an experimental animal. The animal was enclosed in a glass bulb through which fresh air was pumped continuously. After leaving the animal the air passed through an ionization chamber. The varying potential of the chamber was automatically recorded and this potential was calibrated to give the concentration of C14. A number of other experiments were described, including the use of chromatographic adsorption to isolate minute quantities of the radioactive products of photosynthesis. Algae were supplied with carbon dioxide containing C14, light was radiated on the algae for, say, 10 seconds, and the products formed in the algae were separated by chromatography. The variously placed smudges were checked for C14 content and analyzed. Dr. Gamow's lecture was enthusiastically received. His touches of humor and the modest way in which be
put forward his proposals were especially appreciated by those fortunate enough t o hear him speak. To explain his interest as a theoretical physicist in the problems of cell replication he pointed out that biology, especially the biology of heredity, is rapidly becoming an exact science. To provide a background for his theory he illustrated mitosis and showed how the long thread-like molecules of desoxyribonucleic acid consist of long lines of pyrimidines and purines, linked to sugar phosphate chains. These filaments are given a helical twist that repeats every ten steps. The key compounds in the DNA molecule are adenine, thymine, guanine, and cytosine. If these four compounds are numbered one to four, a long and special sequence of four digits, including r a n d 4 may be used to stand, in coded form, for the pattern of a particular living organism. Gamow called this the number of the beast. It is the blueprint in the chromosomes that somehow guides the enzymes toward the peculiar pattern of chemical synthesis that results in an individual similar to others of the species, yet, in many respects, uniquely different. Next, Gamow linked the proposed pattern for the DNA molecule with the number of amino acids which form in proteins. Arranging the numbers one to four spirally on a mailing tube, he saw immediately that he had a series of diamonds, with one of the four digits marking each base. Numerical consideration indicated 20 different kinds of diamonds. Of the thousands of possible amino acids, only 20 should fit into the slots provided. His hypothesis tbus suggests a mechanism whereby the pattern of bases in the chromosomes can be used to stamp out a pattern of amino acids in those proteins that go to build a complete organism. Verification of the theory has been partially successful. The pattern of amino acids in both insulin A and insulin B has been worked out by Sanger. When a possible intersymbol combination (of which there are 10") is compared with the insulin patterns, that for A fits, but that for B does not. In conclusion, Gamom showed some colored slides of beautiful and intricate models by which he had attempted, with only partial success, to portray complete DNA molecules.
