Final answer:
Ran-GDP is transported back to the nucleus, where a guanine nucleotide exchange factor exchanges GDP for GTP on Ran. This is part of the nucleocytoplasmic transport process, which is similar to G-protein-coupled receptor signaling where the Gα subunit exchanges GDP for GTP upon activation.
Step-by-step explanation:
The subject of the question is cell signalling and nucleocytoplasmic transport, specifically regarding Ran-GDP, which is related to G-protein signalling pathways. When Ran-GDP is transported back to the nucleus, it is recognized by nuclear transport receptors that facilitate its passage through the nuclear pore complex. Inside the nucleus, the guanine nucleotide exchange factor (RanGEF) catalyzes the exchange of GDP for GTP on Ran, converting it to Ran-GTP, which then dissociates from the import receptor, allowing the receptor to participate in another round of transport.
In a broader context of signalling pathways, when a signalling molecule binds to a G-protein-coupled receptor (GPCR), the G protein α subunit exchanges GDP for GTP, which leads to a cascade of intracellular events. The Gα-GTP complex can then go on to interact with other effectors such as adenylate cyclase, leading to the production of cAMP and subsequent activation of protein kinase A (PKA), which regulates numerous cellular processes. Eventually, the α subunit hydrolyzes GTP back to GDP, reassociating with the β and γ subunits, becoming ready for another cycle of activation.