Receptors and Cell Signaling

Question 1

To become active, the G protein must exchange its GDP for GTP. What facilitates this?

Answer 1

Guanidine Nucleotide Exchange Factor(GEF)

Question 2

When returning to its inactive state, GPCR hydrolyzes GTP back to GDP. Which enzyme facilitates this?

Answer 2

Intrinsic GTPase

Question 3

Enzyme that accelerates GTPase’s activity?

Answer 3

GAP(GTPase Activating Protein)

Question 4

What do inhibitors of cGMP PDE cause? Give an example

Answer 4

increase cellular concentration of cellular cGMP, leading to smooth muscle relaxation and vasodilation (Viagra, Cialis).

Question 5

How does caffeine increase heart rate?

Answer 5

by inhibiting cAMP PDE.

Question 6

Cholera mechanism

Answer 6

Prevents inactivation of Gs-alpha(ADP ribosylation on Arg): Continuous stimulation on Adenylate Cyclase and overproduction of cAMP.

Question 7

Pertussis mechanism

Answer 7

Prevents activation of Gi-alpha(ADP ribosylation of Cys): Less inhibition of AC and overproduction of cAMP.

Question 8

How do proteins get desensitized?

Answer 8

GRKs phophorylate the GPCRs. Arresting binds to third intracellular loop. Prevents G-alpha from interacting with that loop. G-alpha GDP does not convert to G-alpha GTP.

Question 9

Binding of ligand to ECD of RTK causes____?

Answer 9

Dimerization. These residues phosphorylate Tyrosine residues.