Final answer:
Anti-apoptotic proteins are typically considered oncogenes if their function becomes overactive, as they prevent the necessary cell death that stops cancer cells from growing. Tumor-suppressor genes, on the other hand, serve as the 'brakes' for cell division and their loss of function can lead to cancer.
Step-by-step explanation:
Anti-apoptotic proteins are likely to be considered oncogenes when mutated or overexpressed. The reason behind this classification relates to their function in preventing apoptosis, which is the programmed cell death that occurs when cells are damaged or no longer needed. In a cancerous setting, these proteins might be hyperactive and prevent the apoptosis of cells that should otherwise die, leading to uncontrolled cell proliferation.
An anti-apoptotic protein functioning abnormally would thus lead to overactive cell survival signals, akin to pushing the accelerator pedal in cell life cycles and enabling tumor growth.
In contrast, tumor-suppressor genes act like brakes for cell division and when they lose functionality due to mutations, cells can proliferate uncontrollably. Some of the best-understood tumor suppressor proteins include Rb, p53, and p21, which serve to put a halt to the cell cycle progression in case of issues such as DNA damage. Hence, if tumor-suppressor genes are not working properly, due to mutations or deletions, they fail to provide necessary stop signals and contribute to tumorigenesis.