Answer
Cyclins are proteins that supervise and regulate the cell cycle--including mitosis. They check for DNA damage at certain points in the cell cycle through the agency of check-point proteins like PD-1 and CHK2 (check point kinase 2).
Proto-oncogenes code for proteins that promote/support the cell cycle, and prevent apoptosis (programmed cell death).
Work Step by Step
Tumor suppressor genes also code for checkpoint proteins. In this case, the proteins inhibit the cell cycle and promote apoptosis
Both RAS protein and Cyclin D are coded for by oncogenes that lead to the formation of cyclins which promote mitosis.
