Quick questions on Causes of mutation: physical, chemical and biological mutagens: HSC Biology Module 6

These deliver energy that physically damages DNA.

These are living agents or biological molecules that cause mutations.

Non-ionising, short-wavelength light in the UV-B and UV-C bands. UV photons are absorbed by adjacent pyrimidine bases (especially thymine) on the same strand, causing them to covalently bond as a thymine dimer (a pyrimidine dimer). The dimer distorts the double helix.

Molecules structurally similar to normal bases that are incorporated during replication and mis-pair. Example: 5-bromouracil resembles thymine but pairs with guanine, producing T to C transitions.

Some viruses insert their DNA (or a reverse-transcribed DNA copy of their RNA) into the host genome. The insertion can disrupt a host gene or activate a nearby proto-oncogene. Example: human papillomavirus (HPV) integrates near tumour suppressor genes and causes cervical cancer.

DNA sequences that move within the genome, sometimes inserting into and disrupting other genes. They were discovered by Barbara McClintock in maize. Transposons are responsible for many spontaneous mutations in eukaryotes.

Generated as by-products of normal aerobic metabolism. Oxidise guanine to 8-oxo-guanine, which mis-pairs with adenine and fixes a G to T transversion. These are responsible for much of the spontaneous mutation rate.

Distinguish between a chemical mutagen and a physical mutagen, providing one example of each. [3 marks]

A Sydney laboratory exposes cultured human fibroblasts to UVB for 0, 5, 10 and 20 minutes and counts thymine dimers per million bases as 2, 38, 75 and 144 respectively. Describe the relationship and predict the dimer count at 15 minutes. [3 marks]

A bushwalker is exposed to elevated background radiation from radon at a remote site over a weekend. (a) Identify the type of mutagen radon emits. (b) Describe the molecular damage it causes.