Final answer:
Mitogens facilitate cell cycle progression by overcoming intracellular braking mechanisms, not by directly stopping cell division. They are part of a regulatory system that includes various molecules like Cdks, which are activated to move the cell cycle forward, and tumor suppressor genes that can halt cell division when needed.
Step-by-step explanation:
Mitogens operate by overcoming intracellular braking mechanisms that block progression through the cell cycle. This involves the suppression of certain regulatory molecules that normally function to halt the cell cycle until specific conditions are met. For example, mitogens can activate Cyclin-dependent kinases (Cdks) which are crucial for the progression of the cell cycle. Mitogens do not directly stop cell division, but rather stimulate cell division by indirectly influencing molecules such as p53, p21, and CHK2, which can suppress proteins that regulate the progression through the cell cycle. When these suppressor proteins are inhibited, cells can then proceed through the stages of the cell cycle.
In the context of cancer research, a scientist may find that cancer cells continue to survive even when an inducer of apoptosis is introduced. This could be due to a mutation that prevents the initiation of apoptosis signaling, loss of expression of the receptor for the apoptosis-inducing ligand, or an overexpression of a growth factor pathway that inhibits apoptosis. Additionally, tumor suppressor genes, which also include p53, are important because their primary function is to stop certain cells from dividing when necessary, such as when DNA damage is detected.