2 Molecule \'S\' can bind to a GPCR on the surface of mammalian cells, stimulati

Question

2 Molecule 'S' can bind to a GPCR on the surface of mammalian cells, stimulating them to form actin stress fibers. You have a solution of "S", as well as a solution of GTP-gamma-F, a fictitious non-hydrolysable analog of GTP that can bind to heterotrimeric GTPases. You treat mammalian cells in one dish with molecule 'S' only. At the same time, you treat a second dish containing the same type of cells with both molecule S and GTP-gamma-F. You immediately perform a time-lapse live-cell fluorescence microscopy analysis to image the status of the fluorescing actin cytoskeleton in the same living ce in each of the two dishes immediately before (t0 min) and at three times (5, 10, 15 min) after addition of S, or 'S" plus GTP-gamma-F. (Note, for the purpose of this question, assume (i) that the plasma membrane is freely permeable to GTP-gamma-F; (ii) that GTP and GTP-gamma-F each bind with the same affinity to heterotrimeric G-proteins, and that GTP-gamma-F has no effect on Rho.) Which cell received which compounds? poing t=0min t=5min t=10min t=15min O Cell A received S' plus GTP gamma-F Cell B received-S' only. O Cell B received S' plus GTP-gamma-F; Cell A received S only

Explanation / Answer

The correct answer is option A

This is because in Cell A first S binds to GPCR this activates the reaction after that GTP-gamma-F further activated the G-protein. This dissociates G-protein subunits and signal transduction is seen even after 15 min

While cell B get s only. Thus it activates the reaction and cannot carry forward due to inactivity of G-protein.

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