Final answer:
The first regulatory point of cell division is the G1 checkpoint, also known as the restriction point. Proteins such as Rb, p53, and p21 play crucial roles in regulating the cell cycle at this checkpoint.
Step-by-step explanation:
The first regulatory point of cell division is the G1 checkpoint, also known as the restriction point. At this checkpoint, the cell determines whether all conditions are favorable for cell division to proceed. The G1 checkpoint ensures that cell size, adequate reserves, and genomic DNA damage are suitable for cell division.
Several proteins are crucial for regulating the cell cycle at the G1 checkpoint. The retinoblastoma protein (Rb), p53, and p21 are key regulatory proteins that act at this checkpoint. Rb is a tumor-suppressor protein that helps prevent uncontrolled cell division. p53 is a multi-functional protein that halts the cell cycle and initiates DNA repair or apoptosis in response to damaged DNA. p21 is another regulator protein that enforces the halt in the cell cycle directed by p53 by inhibiting the activity of certain enzyme complexes.
The G1 checkpoint, a pivotal regulatory point in the cell cycle, serves as the initial assessment of conditions favoring cell division. This checkpoint ensures that cell size, resource availability, and genomic DNA integrity meet prerequisites for cellular proliferation. Central to G1 checkpoint control are key regulatory proteins, including retinoblastoma protein (Rb), p53, and p21. Rb functions as a tumor suppressor, curbing uncontrolled cell division. P53, a versatile protein, intervenes in response to DNA damage, either instigating repair processes or inducing apoptosis. Collaboratively, p21 complements p53's role by inhibiting specific enzyme complexes, reinforcing the cell cycle halt directed by p53 and safeguarding genomic stability.