Page 29 - Cell biology PDG 2024

Figure 13: ion channel receptors

2) G protein coupled receptors:

GPCRs are cell surface receptors that act through a G-protein to start a
second messenger cascade, which modulates cellular function

The receptor has the ligand-binding site on the outside of the plasma
membrane and has a transmembrane portion (spanning the plasma
membrane) which can bind to a G-protein in the intracellular space. A G-
protein is a heterotrimeric protein with three subunits, alpha, beta, and
gamma. Both the beta and gamma subunits are attached to the
membrane by a lipid anchor. When no ligand is bound to the receptor,
the alpha subunit and a GDP is bound to the transmembrane receptor
and the beta and gamma subunits

When the ligand binds the receptor, a conformational change occurs
activating the G protein, and a GTP molecule replaces the GDP molecule
on the alpha subunit. The G-protein dissociates with the beta and

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