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Membrane-Bound Receptors that Activate G Proteins

How is cell signaling similar to metabolic pathways such as cellular respiration? Many cellular processes use similar mechanisms to achieve different results. Metabolic pathways are series of enzyme-catalyzed reactions. Enzymes interact to remove and add phosphate groups to molecules or to move protons across a membrane. Similarly in cell signaling, receptor proteins interact with specific molecules and often remove or ad phosphate groups. The phosphorylation of receptor proteins is a very similar process to steps in metabolic pathways but with a very different function. In metabolism phosphorylation is a method of transferring energy, in cell signaling it transmits information.

View the animation below, then complete the quiz to test your knowledge of the concept.






1A ligand is...
A)a small molecule that binds to the alpha subunit of the G-protein.
B)a small molecule that binds to a membrane-bound receptor.
C)a large molecule that binds to the alpha subunit of the G-protein.
D)a large molecule that binds to a membrane-bound receptor.
E)a small molecule that binds to a G-protein.



2Initially, bound to the alpha subunit of the G-protein is...
A)a ligand.
B)a GTP molecule.
C)a GDP molecule.
D)an ADP molecule.
E)a GTO molecule.



3As a result of the ligand binding to its site...
A)the G-protein changes conformation and GTP replaces the GDP on the alpha subunit.
B)the G-protein changes conformation and the alpha subunit separates from the beta and gamma subunits.
C)the G-protein changes conformation and GDP replaces the GTP on the alpha subunit.
D)the G-protein changes conformation and the alpha subunit rejoins the beta and gamma subunits.
E)the G-protein changes conformation and GTO replaces the GTP on the alpha subunit.



4The alpha subunit’s separatism from the remainder of the G-protein can be repeated as long as the ligand is bound to the receptor.
A)True
B)False



5Inactivation of the alpha subunit occurs when its own phosphorylase activity removes a phosphate from the GTP.
A)True
B)False







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