What is the role of G proteins in GPCR signaling?

• A. Catalyzing DNA synthesis.
• B. Initiating apoptosis.
• C. Transcription of mRNA.
• D. Activating downstream effectors.

Answer: (D)

Verified step by step guidance

1. Understand that GPCR stands for G Protein-Coupled Receptor, which is a large family of cell surface receptors that respond to various external signals.
2. Recognize that G proteins are intracellular proteins that bind guanosine triphosphate (GTP) and guanosine diphosphate (GDP) and are involved in transmitting signals from GPCRs to other parts of the cell.
3. When a ligand binds to a GPCR, it causes a conformational change in the receptor, which then activates the associated G protein by facilitating the exchange of GDP for GTP on the G protein.
4. The activated G protein, now bound to GTP, dissociates into its subunits (usually the alpha subunit and the beta-gamma dimer), which then interact with various downstream effectors such as enzymes or ion channels, leading to a cellular response.
5. The role of G proteins in GPCR signaling is to act as molecular switches that activate downstream effectors, thereby propagating the signal initiated by the ligand binding to the GPCR.