Final answer:
In its inactive state, the G-protein is a heterotrimer consisting of alpha, beta, and gamma subunits with GDP bound to the alpha subunit. This structure keeps the G-protein inactive until a signaling molecule interacts with a G-protein-coupled receptor, initiating cell signaling processes.
Step-by-step explanation:
The structure of the G-protein when it's inactive, or in its 'off-form,' consists of three subunits: the alpha (α), beta (β), and gamma (γ) subunits. In this inactive state, the alpha subunit is bound to guanosine diphosphate (GDP), effectively keeping the G-protein in a resting mode.
This configuration is critical in the cell signaling process involving G-protein-coupled receptors (GPCRs). When a signaling molecule binds to the GPCR, it causes a conformational change that allows the GDP to be exchanged for guanosine triphosphate (GTP) on the alpha subunit.
Subsequently, the beta and gamma subunits dissociate from the alpha subunit, which then can activate or inhibit other proteins in the signaling pathway. Eventually, the intrinsic GTPase activity of the alpha subunit hydrolyzes GTP back to GDP, the beta and gamma subunits reassociate with the alpha subunit, and the G-protein returns to its inactive state, ready for another cycle of activation.