Describe the steps by which the TP53 gene responds to DNA damage and/or cellular stress to promote cell-cycle arrest and apoptosis. Given that TP53 is a recessive gene and is not located on the X chromosome, why would people who inherit just one mutant copy of a recessive tumor-suppressor gene be at higher risk of developing cancer than those without the recessive gene?

Key Concepts

TP53 Gene Function

The TP53 gene encodes the p53 protein, which plays a critical role in regulating the cell cycle and maintaining genomic stability. In response to DNA damage or cellular stress, p53 is activated to induce cell-cycle arrest, allowing for DNA repair, or to trigger apoptosis if the damage is irreparable. This function is essential for preventing the proliferation of damaged cells, thereby acting as a tumor suppressor.

Recessive Genes and Tumor Suppression

Recessive genes require two copies of the mutant allele to manifest their effects. In the case of tumor suppressor genes like TP53, inheriting one mutant copy does not immediately lead to cancer, but it predisposes individuals to cancer because the normal allele can still produce functional p53. However, if the remaining normal allele is lost or mutated, the protective function is compromised, increasing cancer risk.

Cell Cycle Regulation and Apoptosis

The cell cycle is a series of phases that a cell goes through to divide and replicate. p53 regulates this process by halting the cycle in response to stress signals, allowing for repair mechanisms to function. If the damage is too severe, p53 can initiate apoptosis, a programmed cell death pathway, to eliminate potentially cancerous cells, thus preventing tumor development.