Which receptor type is typically activated by peptide ligands and signals via G proteins?

Which receptor type is typically activated by peptide ligands and signals via G proteins?

• A. Ion channels.
• B. Intracellular receptors.
• C. Enzyme linked receptors (tyrosine kinase).
• D. G-Protein coupled receptors.

Answer: (D)

Peptide ligands are hydrophilic and cannot cross the cell membrane, so their signals begin at the surface. The receptor that transduces these signals by activating a G protein is the G-Protein Coupled Receptor. When a peptide binds, the receptor activates a heterotrimeric G protein, causing the α subunit to exchange GDP for GTP and modulate downstream effectors such as adenylyl cyclase or phospholipase C. This leads to second messengers like cAMP, IP3, DAG, and Ca2+, producing a regulated cellular response. This metabotropic mechanism is slower and more versatile than signals through ligand-gated ion channels, which gate ions directly and do not use G proteins. Receptor tyrosine kinases are activated by peptide ligands too but signal via phosphorylation cascades rather than G proteins, and intracellular receptors require ligands that cross the membrane.

Peptide ligands are hydrophilic and cannot cross the cell membrane, so their signals begin at the surface. The receptor that transduces these signals by activating a G protein is the G-Protein Coupled Receptor. When a peptide binds, the receptor activates a heterotrimeric G protein, causing the α subunit to exchange GDP for GTP and modulate downstream effectors such as adenylyl cyclase or phospholipase C. This leads to second messengers like cAMP, IP3, DAG, and Ca2+, producing a regulated cellular response. This metabotropic mechanism is slower and more versatile than signals through ligand-gated ion channels, which gate ions directly and do not use G proteins. Receptor tyrosine kinases are activated by peptide ligands too but signal via phosphorylation cascades rather than G proteins, and intracellular receptors require ligands that cross the membrane.