The results will disclose the primary site (DNA, RNA, or proteins) of the drug action on cell metabolism. More elaborate experiments can pinpoint more intimately the mechanism of action. By studying the life processes of cells, we can advance toward a common denominator in anti-cancer drugs that will lead to an effective anti-cancer treatment. CONCLUSIONS _Thus, the task is, not so much to see what no one has seen yet; but to think what nobody has thought yet, about what everybody sees._ Arthur Schopenhauer The use of radioactive isotopes in the study of life processes is of importance in understanding them. With the use of autoradiographic and radiochemical techniques, it is possible to obtain valuable information regarding the life of cells and the intimate mechanisms by which life processes determine the fate of the entire organism. Our knowledge of the cell cycle and of the gene-action system has been useful in determining how organisms grow and how cancer cells behave. It has been determined that certain normal adult cells divide more frequently than some cancer cells and that the growth of cancers depends not so much on the speed of cellular proliferation as on the number of cells actually dividing. [Illustration: Figure 29 _Radioautograph showing DNA synthesis during chromosome replication. Chromosomes from cells in the root tip of the Tradescantia plant were labeled with ³H-thymidine. In A and B, the midportion of DNA synthesis, the radioisotope is distributed throughout the chromosome arms; in C, near the end of DNA synthesis, it is confined mainly to the end of the arms._] Knowledge of the cell cycle has also brought new insight to the control of cell division, as in studies related to the therapy of cancer. The most important problem now is, not the control of cell division, but the control of the synthesis of DNA. Our information on the gene-action system provides broad new opportunity for the investigation of many life processes. Hormone action, processes by which the body develops immunity to disease, and even cell division itself are apparently regulated through the gene-action system. This, in turn, offers possibilities for investigations meant to control these processes. It is difficult to chart the future course of modern molecular biology, but it is not difficult to predict that the next few years will bring to biology the same kind of sweeping advances that revolutionized physics a few decades ago. The DNA molecule has been called the atom of life. When we have harnessed it, the harnessing of the uranium atom will seem, in comparison, a result of scientific adolescence. When man has mastered the genetic code, he’ll hold a vast power in his hands—power over the nature of coming generations. SUGGESTED REFERENCES Books