_____ can be carcinogens.

• A. Hydrocarbons
• B. Alcohol
• C. Oxygen
• D. Nitrogen

Answer: (A)

Carcinogens are substances that can lead to cancer by damaging DNA, and certain hydrocarbons fit this description because some can be activated inside the body into highly reactive forms. Many hydrocarbons, especially polycyclic aromatic hydrocarbons, are not inert once inside the body. Enzymes such as cytochrome P450 can convert them into epoxides and diol epoxides that covalently bind to DNA, forming adducts. If these DNA lesions aren’t repaired, they can cause mutations during cell division. When mutations hit genes that control cell growth, cells can begin to divide uncontrollably, leading to cancer. A classic example is benzo[a]pyrene, a PAH found in tobacco smoke and charred foods, well studied for its carcinogenic effects. Oxygen and nitrogen themselves are essential elements and, on their own, aren’t the typical carcinogens in this context; while reactive oxygen species can contribute to DNA damage, the basic molecules listed aren’t the examples of carcinogens described here.