Biology, Eighth Edition (Raven)

Chapter 9: Cell Communication

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.



1.

A 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.
2.

Initially, 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.
3.

As 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.
4.

The 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
5.

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