Final answer:
Tumor suppressor genes code for regulatory proteins that halt cell division, preventing uncontrolled growth. When mutated, these genes fail to control cell division, which can lead to cancer, as seen with defective p53 proteins.
Step-by-step explanation:
Tumor suppressor genes are crucial segments of DNA that are responsible for producing proteins that regulate the cell cycle, particularly by putting a stop to cell division at various checkpoints. These genes ensure that cell division does not occur uncontrollably, functioning much like a set of brakes in a car. When a mutation affects these genes, the resulting proteins may be unable to perform their role, essentially removing the 'brakes' and leading to unregulated cell division. This malfunction can lead to cancer due to the unchecked proliferation of cells.
One of the key proteins coded by tumor suppressor genes is the p53 protein. Normally, p53 is involved in monitoring DNA and, upon detecting damage, can trigger repair mechanisms or signal for the cell to be destroyed, thereby suppressing tumor formation. However, if the p53 gene is mutated, the p53 protein becomes defective and fails to halt cell division in response to DNA damage. This results in an increased mutation rate and the spread of abnormal cells, eventually disabling all cellular checkpoints and allowing these abnormal cells to outcompete normal cells.
It is the critical balance between proto-oncogenes, which promote cell division, and tumor suppressor genes, which inhibit it, that maintains normal cellular proliferation. Disruption of this balance through mutations in tumor suppressor genes can lead to cancer, as cells divide without the necessary regulatory input that would normally prevent tumor growth.