IB Biology: C2.1-G Protein-Coupled Receptors Concepts

Why are G protein-coupled receptors (GPCRs) also known as Seven Transmembrane Receptors?

• They pass through the cell membrane seven times.

• They are composed of seven different protein subunits.

• They bind to seven distinct types of ligands.

• They are found in seven different cellular locations.

In its inactive state, what molecule is the alpha subunit of the G protein bound to?

• GDP

• GTP

• ATP

• ADP

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When an external signal activates a G protein-coupled receptor (GPCR), what immediate change occurs in the alpha subunit of the G protein?

• It exchanges GDP for GTP.

• It exchanges GTP for GDP.

• It detaches completely from the receptor.

• It binds to the beta and gamma subunits.

What process leads to the inactivation of the G protein after the ligand is removed from the GPCR?

• The alpha subunit hydrolyzes GTP back to GDP.

• The beta and gamma subunits re-bind to the receptor.

• The entire G protein complex is degraded.

• The receptor permanently detaches from the cell membrane.