University of Toronto (UofT) BIO230H1 From Genes to Organisms Midterm Practice Exam

The involvement of GEF (Guanine nucleotide Exchange Factors) and GAP (GTPase-Activating Proteins) in the regulation of monomeric GTPases is central to understanding their function in cellular processes. Monomeric GTPases, which include important proteins like Ras, Rho, and Rac, act as molecular switches that regulate various cellular activities such as cell growth, differentiation, and cytoskeletal dynamics.

GEFs facilitate the exchange of GDP for GTP on the GTPase, thereby activating it. When GTP is bound, the GTPase is in its active form and can interact with downstream effectors to carry out its biological functions. Conversely, GAPs accelerate the hydrolysis of GTP to GDP, which inactivates the GTPase, turning off its signaling capacity. The dynamic interplay between GEFs and GAPs is what allows for precise control over the timing and duration of GTPase activity in response to cellular signals.

In contrast, while kinases and phosphatases are crucial for phosphorylation and dephosphorylation processes that can influence a variety of signaling pathways, they do not directly regulate monomeric GTPases. SNAREs and Rab proteins are involved in vesicle