Which of the following describe the effects of GMP-PnP onprotein import? A. Stal

Question

Which of the following describe the effects of GMP-PnP onprotein import? A. Stalled complex of (mRNA+Ribosome) in cytosol B. Stalled complex of (mRNA+Ribosome+SRP) in cytosol C. Stalled complex of (mRNA+Ribosome+SRP+SRP-receptor) incytosol D. Stalled complex of (mRNA+Ribosome+SRP+SRP-receptor) on ERmembrane E. Inhibit import into Chloroplasts F. Inhibit import into Peroxisomes Which of the following describe the effects of GMP-PnP onprotein import? A. Stalled complex of (mRNA+Ribosome) in cytosol B. Stalled complex of (mRNA+Ribosome+SRP) in cytosol C. Stalled complex of (mRNA+Ribosome+SRP+SRP-receptor) incytosol D. Stalled complex of (mRNA+Ribosome+SRP+SRP-receptor) on ERmembrane E. Inhibit import into Chloroplasts F. Inhibit import into Peroxisomes

Explanation / Answer

D. Stalled complex of (mRNA+Ribosome+SRP+SRP-receptor) on ERmembrane GMP-PNP A non-hydrolyzable analog of GTP, in which the oxygen atombridging the beta to the gamma phosphate is replaced by a nitrogenatom. It binds tightly to G-protein in the presence of Mg2+. Thenucleotide is a potent stimulator of adenylatecyclase. The GTP-binding proteins or GTPases comprise a superfamilyof proteins that provide molecular switches in numerous cellularprocesses. The “GTPase switch” paradigm, in which aGTPase acts as a bimodal switch that is turned “on” and“off” by external regulatory factors, has been used tointerpret the regulatory mechanism of many GTPases for more thantwo decades. Nevertheless, recent work has unveiled an emergingclass of “multistate” regulatory GTPases that do notadhere to this classical paradigm. Instead of relying on externalnucleotide exchange factors or GTPase activating proteins to switchbetween the on and off states, these GTPases have the intrinsicability to exchange nucleotides and to sense and respond toupstream and downstream factors. In contrast to the bimodal natureof the GTPase switch, these GTPases undergo multiple conformationalrearrangements, allowing multiple regulatory points to be builtinto a complex biological process to ensure the efficiency andfidelity of the pathway. We suggest that these multistateregulatory GTPases are uniquely suited to provide spatial andtemporal control of complex cellular pathways that require multiplemolecular events to occur in a highly coordinatedfashion.

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