I am not sure how to approach those review questions and I am especially stuck on 1,2,3

Question

1. What is a possible reason why a misfolded protein may accumulate in a cell?
2. Does cAMP act as an activator or inhibitor for protein kinase A?
3. How does a G-protein binding to GDP vs. GTP change its shape?

Answer 1

1. Misfolded proteins have their hydrophobic groups sticking out; this will cause them to clump together to escape the cell's hydrophilic environment.
2. cAMP activates protein kinase A. cAMP binds to the regulatory subunits of protein kinase A, allowing the catalytic subunits to be released. The catalytic subunits then can activate downstream proteins by phosphorylating them. Hence, it is a kinase.
3. When G protein binds to GTP, the shape or conformation of the G proteins changes to bind to an effector protein (e.g., adenylate cyclase). The G protein's alpha subunit has a hydrolytic activity, which hydrolyzed the GTP to become GDP. This is a regulatory function of the G protein so that it can turn off after it finishes its job.