Mutagen

Chemical mutagens are classified as alkylating agents, cross-linking agents, and polycyclic aromatic hydrocarbons (PAHs). Alkylating agents act by adding molecular components to DNA bases, which alters the protein product. Cross-linking agents create covalent bonds with DNA bases, while PAHs are metabolized by the human body into other potentially mutagenic molecules.

Radiation is another potent mutagen. For biologists, the most significant forms of radiation are light, heat, and ionizing radiation. Ionizing radiation can penetrate cells and create ions in the cell contents. These, in turn, can cause permanent alterations in DNA; that is, mutations. Ionizing radiation includes: x rays, gamma rays, and the subatomic particles—neutrons, electrons ("beta" particles), and alpha particles (helium nuclei). Ionizing radiation alters the way two strands of DNA interact. This high energy radiation passes through cells and tissues, cutting up any DNA in its path. It can rearrange entire sections of the chromosomes, altering relatively long stretches of DNA. UV radiation causes covalent bonds to form between neighboring thymine bases in the DNA, so altering the DNA product at that location.

Mutagens are often associated with specific cancers in humans. Aromatic amines are mutagens that can cause bladder cancer. Tobacco taken in the form of snuff contains mutagens that can cause nose tumors. Tobacco smoke contains mutagens such as PAHs and nitrosamine (a type of alkylating agent), as well as toxins such as carbon monoxide, cyanide, ammonia, arsenic, and radioactive polonium. Although tobacco products are legal and widely available, many physicians and government agencies warn about the health risks linking smoking with several types of cancer and heart disease.

In 1973, Bruce Ames introduced the most widely-used test to identify potential mutagens. Suspected mutagens are mixed with a defective strain of the bacteria Salmonella, which only grows if it is mutated. Substances that allow the Salmonella to grow are considered mutagenic.