Final answer:
Cancer arises from a breakdown of the mechanisms that regulate the cell cycle, resulting in unchecked cell division. Mutations in genes coding for regulatory molecules, such as the p53 protein, can lead to dysfunctional proteins that fail to stop cell division when DNA is damaged. As a result, abnormal cells accumulate and tumors form.
Step-by-step explanation:
Cancer arises from a breakdown of the mechanisms that regulate the cell cycle, resulting in unchecked cell division. This breakdown is caused by changes in the DNA sequence of genes coding for regulatory molecules. These changes lead to faulty instructions and proteins that do not function properly.
One example of a regulatory molecule is the p53 protein, which plays a major role in monitoring DNA for damage during the G₁ checkpoint. Mutations in the p53 gene can result in abnormal p53 proteins that fail to stop cell division when DNA is damaged, leading to an increased number of mutations and abnormal daughter cells.
Over time, all checkpoints in the cell become nonfunctional, leading to the crowding out of normal cells by rapidly reproducing abnormal cells and the formation of tumors or leukemia.