Answer:
G proteins, or guanine nucleotide-binding proteins, are a family of proteins involved in intracellular signal transduction. They are crucial in transmitting signals from cell surface receptors, such as G protein-coupled receptors (GPCRs), to intracellular effector proteins.
Step-by-step explanation:
G proteins have three subunits: α, β, and γ. The α subunit binds guanine nucleotides, specifically GDP (guanosine diphosphate) when inactive and GTP (guanosine triphosphate) when active. The β and γ subunits are tightly associated and function as a dimer.
When a ligand, such as a hormone or a neurotransmitter, binds to a GPCR on the cell surface, it triggers a conformational change in the receptor. This change allows the activated GPCR to interact with the G protein and promote the exchange of GDP for GTP on the α subunit. This process is facilitated by the GPCR acting as a guanine nucleotide exchange factor (GEF).