Carcinogen
Definition and meaning of Carcinogen in chemistry.
A carcinogen is any substance or physical agent that can cause cancer by damaging DNA or otherwise disrupting the normal regulation of cell growth and division.
In more detail
Many chemical carcinogens are not reactive themselves but require metabolic bioactivation, often by cytochrome P450 enzymes in the liver, which converts them into electrophilic intermediates. These reactive species covalently bind DNA bases to form bulky adducts; if unrepaired, the adducts cause mutations during replication, sometimes in genes that control cell division, such as tumor suppressor genes. Other carcinogens act nongenotoxically, promoting cancer by driving chronic inflammation or excessive cell proliferation rather than damaging DNA directly. Carcinogenic risk depends on dose, exposure duration, and the balance between DNA damage and cellular repair.
Key facts
| Field | Biochemistry |
|---|---|
| IARC Group 1 examples | asbestos, benzene, benzo[a]pyrene |
| Primary mechanism | DNA adduct formation leading to mutation |
| Common bioactivation route | Cytochrome P450 metabolism |
Benzo[a]pyrene, a polycyclic aromatic hydrocarbon in tobacco smoke and charred meat, is oxidized by cytochrome P450 enzymes into benzo[a]pyrene diol epoxide, a reactive species that binds guanine in DNA and can cause mutations in the p53 tumor suppressor gene.
Frequently asked questions
Are all carcinogens also mutagens?
No. Most potent carcinogens are mutagens that damage DNA directly, but some, called nongenotoxic or epigenetic carcinogens, promote cancer by stimulating cell proliferation or blocking cell death without directly altering the DNA sequence.
How are carcinogens officially classified?
The International Agency for Research on Cancer (IARC) sorts agents into Group 1 (carcinogenic to humans), Group 2A (probably carcinogenic), Group 2B (possibly carcinogenic), and Group 3 (not classifiable) based on epidemiological and mechanistic evidence.