119 Mutagens

Key Idea: Mutagens are any chemical or physical agent that causes a change in the DNA sequence.

The natural rate at which a gene will undergo a change is normally very low, but this rate can be increased by chemical or physical agents called mutagens, which alter the DNA sequence. Mutagens and their effects and outlined below:

Ionising radiation

Ionising radiation is associated with the development of cancers, e.g. thyroid cancers, and skin cancer. It includes alpha, beta and gamma radiation from nuclear decay. UV radiation from the sun and tanning lamps. X-rays and gamma rays from medical diagnosis and treatment.

Viruses and microorganisms

Some viruses integrate into the human chromosome, upsetting genes and triggering cancers. Examples include hepatitis B virus (liver cancer), Hodgkin’s disease, and HPV (right) which is implicated in cervical cancer. Aflatoxins produced by the fungus Aspergillus flavus are potent inducers of liver cancer.

Poisons and irritants

Many chemicals are mutagenic. Synthetic and natural examples include organic solvents such as benzene, asbestos, formaldehyde, tobacco tar, vinyl chlorides, coal tars, some dyes, and nitrites. Photo right: Firefighters and those involved in environmental clean-up of toxic spills are at high risk of exposure to mutagens.

Diet, alcohol and tobacco

Diets high in fat, especially those containing burned or preserved meat are important causes of colon cancer. High alcohol and tobacco tar intake are known causes of cancer. Tobacco tars contain at least 17 known carcinogens (cancer inducing mutagens). 1. Describe examples of environmental factors that induce mutations under the following headings:

(a) Radiation:

(b) Chemical agents:

2. How do mutagens cause mutations?

3. Explain why people such as radiographers, or even dentists have at a higher risk of exposure to cancer causing radiation: