Question

You turn on a light so you can get a glass of water. At the moment the light turns on, the relative amount of Gα-GDP of trimeric G proteins __________.

Option 1: Increases
Option 2: Decreases
Option 3: Remains constant
Option 4: Fluctuates randomly

Answer 1

The amount of Gα-GDP of trimeric G proteins decreases when you turn on a light, as GTP replaces GDP on the α subunit upon activation of the G protein transducing due to light exposure, leading to cellular responses.

Step-by-step explanation:

When you turn on a light and stimulate photoreceptor cells in the eye, the relative amount of Gα-GDP of trimeric G proteins decreases. This occurs because light activation of rhodopsin leads to the activation of the G protein transducing. Once activated, GTP replaces GDP on the α subunit of the G protein, leading to the dissociation of the β and γ subunits from the α subunit, and initiating a cellular response, such as the conversion of cGMP to GMP by phosphodiesterase, ultimately causing hyperpolarization. The hydrolysis of GTP back to GDP will eventually terminate the signal and allow the subunits to reassociate, preparing the G protein for another cycle of activation and deactivation.