Question

mutations in the kras gene are frequently found in colon cancer. these mutations are always missense mutations, primarily in codons 12 or 61. mutations in the apc gene are also associated with colon cancer. in this case, however, nonsense and frameshift mutations are frequent and are scattered throughout most of the coding region.Is KRAS an oncogene or a tumor-suppressor gene?

Answer 1

The KRAS gene is a proto-oncogene, and when mutated, it acts as an oncogene leading to cancer by promoting cell proliferation. APC and TP53 are examples of tumor-suppressor genes, which when mutated, lose their ability to control cell division and lead to cancer.

Step-by-step explanation:

The KRAS gene is an example of a proto-oncogene, which when mutated, can lead to cancer by continuously activating cell proliferation signals. This is in contrast to tumor-suppressor genes like APC and TP53, which normally act to inhibit cell division and promote apoptosis. Mutations in tumor-suppressor genes lead to a loss of function, allowing cells to divide uncontrollably. KRAS mutations that are frequently found in colon cancer are missense mutations that lead to a gain of function, which aligns with the behavior of an oncogene.

In contrast, mutations in the APC gene associated with colon cancer frequently involve nonsense and frameshift mutations that inactivate the gene and its tumor-suppressing functions. The TP53 gene, which codes for the tumor suppressor protein p53, when mutated, is associated with many forms of cancer since it normally functions to regulate the cell cycle and induce apoptosis in damaged cells. Studies such as those on Li-Fraumeni syndrome (LFS) patients, who have a mutated TP53 allele, demonstrate the critical role of tumor suppressor genes in cancer prevention.