至于辐射? 什么意思？烟草烟雾有什么辐射？

Tobacco Smoke Carcinogens

Tobacco smoke contains 44 known human carcinogens, but two groups are of significance to the formation of lung cancer, polycyclic aromatic hydrocarbons and nitrosamines.As for radiation, much of the molecular damage is caused by the carcinogens generating reactive oxygen species. The normal defence mechanisms (page 289) are overwhelmed, and DNA, RNA, lipids and protein molecules are damaged by oxidation reactions. Many tobacco carcinogens also directly react with DNA either by causing methylation of bases within the DNA or simply by forming adducts between themselves and the DNA molecule. These various chemical changes to the DNA molecule will either interfere with transcription immediately or induce mutations when the DNA replicates during subsequent cell divisions, explaining why rapidly dividing cells are more susceptible to malignant change.

烟草烟雾致癌物质

烟草烟雾含有44种已知的人类致癌物质，其中有两类对肺癌的形成具有重要意义，即多环芳烃和亚硝胺。至于辐射，大部分分子损伤是由辐射产生的活性氧造成的。在致癌物的影响下，正常的防御机制（第289页）不堪重负，DNA、RNA、脂质和蛋白质分子被氧化反应破坏。许多烟草致癌物或通过引起DNA内碱基的甲基化，或仅通过它们与DNA分子之间形成加合物，而直接与DNA反应。DNA分子的这些化学变化可以立即干扰转录，也可以在随后的细胞分裂中DNA复制时引发突变，这也解释了为什么快速分裂的细胞更容易恶变。

1.至于辐射 什么意思？烟草烟雾有什么辐射？

2.正常的防御机制（第289页）不堪重负，是指被辐射压倒，还是被烟草致癌物压倒