Gene mutations
A gene mutation is a change to the sequence of bases in DNA. Since that base sequence determines the order of amino acids in a polypeptide, a mutation may alter the polypeptide encoded by the gene.
Mutations can arise spontaneously, including when mistakes occur as DNA is replicated.
The effect varies between mutations. Some leave the encoded amino acid sequence unchanged, whereas others change one or several triplets.
Mutagenic agents
A mutagenic agent increases how frequently mutations occur in DNA. Exposure to mutagens can therefore increase mutation rate.
| Type of mutagen | Effect on DNA | Examples covered |
|---|---|---|
| Physical | Physical factors such as radiation can increase DNA mutation frequency. | Alpha and beta radiation, UV, X-rays and gamma rays. |
| Chemical | Chemical substances can interfere with DNA molecules. | Alcohol, benzene, substances associated with asbestos and chemicals in tobacco tar. |
| Biological | Organisms or biological molecules can interfere with DNA. | Viruses; HPV is an example associated with cervical cancer. |
An approximate mutation rate given is one mutation for every 100,000 genes per generation.
Exam Tip: Keep mutagen and carcinogen distinct. A mutagen increases the occurrence of DNA mutations, but this does not mean every mutation caused by a mutagen results in cancer.