Answer to Question #340299 in Genetics for Dds

Question

Distinguish between proto-oncogens and tumor-suppressor genes; give one example of each. In

which class of genes does a loss-of-function mutation predispose cancer? A gain-of-function

mutation? Explain your answer.

Answer 1

• Proto-oncogenes are genes that, when mutated, can turn a healthy cell into a cancerous one. At the same time, tumor-suppressor genes are genes that prevent the development of cancer by participating in the correction of mutations in proto-oncogenes.
• An example of proto-oncogenes is the ANAPC1 gene, which encodes the first subunit of the APC/C complex, which is involved in the exit of the cell from the division phase. In addition, an example of a tumor-suppressor gene is the gene encoding the p53 protein, which is involved in repairing damage to the DNA of proto-oncogenes while preventing proto-oncogenes from becoming oncogenes.
• Cancer will develop if a loss-of-function mutation occurs in both proto-oncogenes and tumor-suppressor genes. After all, for example, such a mutation in the ANAPC1 gene will lead to the formation of a non-functional APC/C complex, which cannot function without the first subunit. The same mutation in the gene encoding the p53 protein will result in the p53 protein not being synthesized.
• As for the gain-of-function mutation, the same pattern can be traced as with the loss-of-function mutation. If a gain-of-function mutation occurs in a proto-oncogene such as ANAPC1, then the first subunit of the APC/C complex, although it will be synthesized, it will have a completely different function and will not be able to enter the APC/C complex, which means that this complex will be released in an inactive state and cancer will develop. But if the same mutation occurs in a tumor-suppressor gene such as the gene that codes for the p53 protein, then, accordingly, the p53 protein will be synthesized with a completely different function, which will not be characterized by the correction of DNA damage, in which case cancer will also develop.