Which of the following proteins would stop the cell cycle, and why would it stop the cell cycle?

• A. Cyclin-dependent kinase (CDK)
• B. p53
• C. Growth factor
• D. Cyclin

Answer: (B)

Verified step by step guidance

1. Understand the role of each protein listed in the options. Cyclin-dependent kinases (CDKs) are enzymes that, when activated by cyclins, promote progression through the cell cycle. Growth factors are signaling molecules that stimulate cell growth and division. Cyclins are proteins that regulate the cell cycle by activating CDKs.
2. Focus on the protein p53. p53 is a tumor suppressor protein that plays a critical role in controlling the cell cycle. It is often referred to as the 'guardian of the genome' because it can prevent the proliferation of cells with damaged DNA.
3. Learn how p53 functions in the cell cycle. When DNA damage is detected, p53 is activated and can induce cell cycle arrest, allowing time for DNA repair. If the damage is irreparable, p53 can initiate apoptosis, or programmed cell death, to prevent the propagation of damaged cells.
4. Consider why p53 would stop the cell cycle. The primary reason p53 halts the cell cycle is to maintain genomic integrity. By stopping the cycle, p53 ensures that cells do not divide with damaged DNA, which could lead to cancerous growth.
5. Conclude that among the options provided, p53 is the protein that would stop the cell cycle due to its role in monitoring DNA integrity and preventing the division of cells with genetic damage.