生物体的外环境中存在着许多致癌物质。目前认为这些致癌物质的作用靶子主要是细胞内遗传的基础物质DNA。它们使DNA的结构发生改变,从而造成损伤。因此,长期接触致癌物质,使癌瘤发生的可能性有所增加。然而尽管存在如此多的致癌因子,实际上在自然条件下患癌瘤者毕竟是少数,这除了在某些情况下致癌物可经代谢而失活外,还有力地说明了生物体细胞内存在着DNA损伤的修复机制。正是这种修复机制,使生物体细胞保持了相对稳定的遗传学 There are many carcinogens in the external environment of living organisms. At present, the role of these carcinogens as the target is mainly based on intracellular genetic material DNA. They change the structure of DNA, causing damage. Therefore, long-term exposure to carcinogens, so that the possibility of cancer has increased. However, in spite of the existence of so many oncogenic factors, in fact, there are only a few cases of cancer under natural conditions, which in addition to the inactivation of carcinogens can be metabolized in some cases, DNA damage repair mechanism. It is this repair mechanism that allows the organism cells to maintain a relatively stable genetics