A G protein is a type of protein that plays a crucial role in transmitting signals from outside the cell to its interior. These proteins act as molecular switches, toggling between an active and inactive state in response to various stimuli, such as hormones or neurotransmitters. When activated, G proteins can influence various cellular processes, including growth, metabolism, and gene expression. G proteins are typically associated with G protein-coupled receptors (GPCRs), which are located on the cell membrane. When a ligand binds to a GPCR, it activates the G protein, leading to a cascade of biochemical events inside the cell. This signaling pathway is essential for many physiological functions and is a target for numerous drugs.