G protein

This term refers to a specific class of heterotrimeric proteins essential for signal transduction in eukaryotic cells. It is used exclusively within biological and biochemical contexts to describe the mechanism by which extracellular signals are converted into intracellular responses.

Because it is a technical scientific term, it is typically used in a countable sense when referring to different types or subunits of the protein (e.g., Gs, Gi, Gq), but often appears in a general sense when discussing the overall signaling pathway.