AP BIOLOGY

Detailed explanation-1: -Answer and Explanation: A cell with a defective p53 gene is likely to stop responding to growth regulators. This is because such a cell is less likely to halt the cell cycle in response to DNA damage. This would likely lead to the development of cancer.

Detailed explanation-2: -Mutations (changes) in the p53 gene may cause cancer cells to grow and spread in the body. These changes have been found in a genetic condition called Li-Fraumeni syndrome and in many types of cancer. The p53 gene is a type of tumor suppressor gene.

Detailed explanation-3: -Inactivation of the p53 tumor suppressor is a frequent event in tumorigenesis. In most cases, the p53 gene is mutated, giving rise to a stable mutant protein whose accumulation is regarded as a hallmark of cancer cells.

Detailed explanation-4: -Activated p53 promotes cell cycle arrest to allow DNA repair and/or apoptosis to prevent the propagation of cells with serious DNA damage through the transactivation of its target genes implicated in the induction of cell cycle arrest and/or apoptosis.

Detailed explanation-5: -In normal cells, the p53 protein level is low. DNA damage and other stress signals may trigger the increase of p53 proteins, which have three major functions: growth arrest, DNA repair and apoptosis (cell death). The growth arrest stops the progression of cell cycle, preventing replication of damaged DNA.