Some forms of cancer are caused by viruses that trigger the formation of tumors. These can be either RNA- or DNA-based viruses. A target gene is the proto-oncogene that normally functions to regulate how cells differentiate and to produce growth factors that regulate cell division. These viruses induce changes in proto-oncogenes, triggering them to become cancer-causing genes, or oncogenes. When oncogenes are expressed, cells divide more rapidly than normal and do not differentiate and mature as usual. Thus, a cancerous tumor has been produced.
Scientists now believe that viruses are involved in 90-95% of all cervical cancers, and that these viruses produce other types of genital tumors. The human papillomaviruses that cause genital warts (some of the lesions of which are flat and go completely unnoticed) are the likely culprits that also trigger these forms of cancer.
How can students keep from acquiring or passing on such viruses?
Chapter 8 covers topics concerning gene technology, but to stimulate student curiosity about this topic in advance, discuss with them some of the fascinating changes that are now occurring in the field of agriculture and medicine as a result of knowing the structure of DNA.
For example, it has been possible to insert genes into crop plants to confer resistance to the active ingredient (glyphosate) in the herbicide Roundup. This is beneficial because the field does not have to be tilled to reduce competitive weeds, thus saving the soil from eroding. Glyphosate is readily degraded by the environment and poses little long-term threat of contamination. Other plants have been made resistant to their own insect pests so dangerous pesticides are not needed.
Many medical advances have resulted from knowing the structure of DNA and how to manipulate genes. Human insulin can now be mass-produced by bacteria, and vaccines will be safer when only the gene coding for a pathogen's surface protein is used to create a vaccine, rather than a killed or attenuated live virus.