Question

20. Mutant Saccharomyces cerevisiae cells that lack the gene encoding securin can divide more or less normally by mitosis, without significant chromosomes segregation defects. Cells harboring a nondegradable version of securin, on the other hand, arrest in metaphase as expected, since they cannot activate separase to enter anaphase. similarly, cells lacking Cdc20 arrest in metaphase, since they cannot activate APC/C. Finally, cells lacking both securin and Cdc20 arrests in anaphase: they manage to seperate sister chromatids, but do not progress much further. These results suggest that in wild-type cells, ...

Answer 1

The p53 gene plays a critical role in the cell cycle’s G1 checkpoint, and its loss leads to uncontrolled cell division, accumulation of mutations, and ultimately, cancer. The absence of p53 function allows cells to bypass checks, resulting in mutated daughter cells that promote tumor growth.

Step-by-step explanation:

Cell Cycle Control and the Impact of p53 Gene Mutations

The mechanisms controlling the cell cycle are critical for maintaining the stability and integrity of the genetic material during cell division. Proteins like p53 play a vital role in this process by acting as a tumor suppressor. When p53 function is lost, the G1 checkpoint of the cell cycle is compromised, allowing cells to proceed from G1 to S phase without the necessary checks. The role of p53 in triggering the production of p21 is crucial for inhibiting Cdk activation, which otherwise would push the cell past checkpoints prematurely. Without an effective block on Cdk activation, cell division occurs under non-optimal conditions, leading to daughter cells with inherited mutations, including the faulty p53 gene. These mutations can accumulate over time, leading to an increase in oncogenes and a decrease in functional tumor suppressor genes, resulting in tumor growth. Additionally, cells that have compromised cell cycle controls due to mutations in critical genes like p53 can contribute to this unchecked cell division, which is a hallmark of cancer.