What occurs when proto-oncogenes are mutated?

When proto-oncogenes are mutated, they can become oncogenes, which are known for promoting excessive cell growth and division. Proto-oncogenes typically play a crucial role in normal cell functions, including cell proliferation and differentiation. However, when these genes undergo mutations—whether through point mutations, amplifications, or chromosomal rearrangements—they can become hyperactive or overexpressed. As a result, the regulatory mechanisms that usually maintain balanced cell growth are disrupted, leading to uncontrolled cell division which is a hallmark of cancer.

In contrast, tumor suppressor genes function to inhibit cell growth and division. If proto-oncogenes were to become tumor suppressor genes (as suggested in one of the options), they would not contribute to cancer development; instead, they would help prevent it. Additionally, a mutation that permanently stops cell division or promotes apoptosis would not align with the function of mutated proto-oncogenes, which instead facilitate increased cell proliferation when they become oncogenes.