What receptor associates with a G protein on the cell surface?

The correct answer is the G protein-coupled receptor (GPCR). These receptors are a large family of membrane receptors that play a critical role in cell signaling. They are characterized by their seven transmembrane alpha-helices and are involved in transmitting signals from a variety of external stimuli through the activation of G proteins.

When a ligand, such as a hormone or neurotransmitter, binds to a GPCR on the cell surface, it induces a conformational change in the receptor. This change allows the GPCR to activate an associated G protein by exchanging GDP for GTP on the G protein, resulting in the initiation of a signaling cascade inside the cell. This process is crucial for the regulation of numerous physiological processes, including sensory perception, immune responses, and mood regulation.

In contrast, ion channel receptors directly open to allow ions to flow across the membrane upon ligand binding, thereby mediating fast synaptic transmission rather than activating G proteins. Nuclear receptors, which are typically located within the cell, bind to steroid hormones and other lipophilic substances and then directly influence gene expression, rather than interacting with G proteins. Receptor tyrosine kinases function through dimerization and subsequent phosphorylation of tyrosine residues to propagate signals, rather than through G