When the signal binds to the receptor, how do G-proteins become active?

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Multiple Choice

When the signal binds to the receptor, how do G-proteins become active?

G proteins are turned on when the receptor acts as a guanine nucleotide exchange factor, causing GDP to be released and GTP to bind to the alpha subunit. In the resting state, the G protein is bound to GDP and is inactive. When the signal binds the receptor, the receptor facilitates the exchange of GDP for GTP on the α subunit, triggering a conformational change that often leads to the dissociation of the α subunit from the βγ dimer. The GTP-bound α subunit (and sometimes the free βγ complex) then interact with downstream effectors to propagate the signal. The intrinsic GTPase activity later hydrolyzes GTP back to GDP to reassemble the inactive complex, turning the system off. So the key step that activates the G protein is exchanging GDP for GTP.

G proteins are turned on when the receptor acts as a guanine nucleotide exchange factor, causing GDP to be released and GTP to bind to the alpha subunit. In the resting state, the G protein is bound to GDP and is inactive. When the signal binds the receptor, the receptor facilitates the exchange of GDP for GTP on the α subunit, triggering a conformational change that often leads to the dissociation of the α subunit from the βγ dimer. The GTP-bound α subunit (and sometimes the free βγ complex) then interact with downstream effectors to propagate the signal. The intrinsic GTPase activity later hydrolyzes GTP back to GDP to reassemble the inactive complex, turning the system off. So the key step that activates the G protein is exchanging GDP for GTP.

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