Which extracellular signal proteins trigger a wave of G1/S-Cdk activity?

Mitogens are extracellular signals that stimulate cell division by triggering the activation of cyclin-dependent kinases (Cdks) involved in the transition from the G1 phase to the S phase of the cell cycle. When cells receive a mitogenic signal, they respond by promoting the expression of various genes that prepare the cell for division. This response often leads to an increase in G1/S-Cdk activity, which is crucial for the progression through the cell cycle.

Once mitogens bind to specific receptors on the cell surface, they lead to a cascade of intracellular signaling events that ultimately result in the activation of G1/S-Cdks. These kinases, in conjunction with their associated cyclins, phosphorylate target proteins necessary for DNA replication and other processes associated with cell division. This wave of activity is essential for cells to commit to entering the S phase and to ensure proper cell proliferation.

While other choices like growth factors may also contribute to cellular processes, mitogens specifically play a direct and critical role in driving the cell cycle, particularly the transition from G1 to S phase.