THE CELL
CELL COMMUNICATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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GDP replaces GTP
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it is bound by its ligand and transported to the nucleus
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it is phosphorylated by protein kinase
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GTP is bound to it
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Ca2+ binds to a G-protein-linked receptor
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Detailed explanation-1: -Whenever a G protein is active, both its GTP-bound alpha subunit and its beta-gamma dimer can relay messages in the cell by interacting with other membrane proteins involved in signal transduction.
Detailed explanation-2: -When GTP is bound to the G-protein, the subunit dissociates from the complex and activates the G-protein. Following activation, both the GTP-bound subunit and the free complex can bind to downstream effector molecules and mediate a variety of responses in the target cell.
Detailed explanation-3: -G proteins are molecular switches that are active in the GTP-bound form, are capable of hydrolyzing the GTP-bound nucleotide to GDP, and in the GDP-bound form are inactive.
Detailed explanation-4: -Upon activation by a ligand, the receptor binds to a partner heterotrimeric G protein and promotes exchange of GTP for GDP, leading to dissociation of the G protein into and subunits that mediate downstream signals.
Detailed explanation-5: -The activated receptor causes heterotrimeric G protein activation (Fig. 1) by causing GDP release from its binding site on the G subunit. GTP binds to G, and G-GTP has reduced affinity for G and receptor; both G-GTP and G are then free to activate downstream effectors.