Final Answer:
Before cell activation with a ligand, the G protein is in an inactive state. It consists of three subunits: α, β, and γ. Ligand binding induces a conformational change, activating the G protein.
Step-by-step explanation:
Before the cell is activated with a ligand, the G protein exists in an inactive or resting state. The G protein is a crucial component of cell signaling pathways, particularly those involving G protein-coupled receptors (GPCRs). In its inactive state, the G protein consists of three subunits: α, β, and γ. When a ligand, such as a hormone or neurotransmitter, binds to the GPCR on the cell membrane, it induces a conformational change in the receptor.
This change allows the G protein to bind to the activated receptor, causing the α subunit to release GDP and bind GTP. This activates the G protein, leading to the dissociation of the Gα subunit from the βγ subunits. Both the activated Gα and the βγ subunits can then modulate downstream signaling cascades, initiating cellular responses. The activation of G proteins is a key step in various cellular processes, including neurotransmission, hormone signaling, and immune responses.