Nbde biochem question

[target]

Hi
can anyone answer this?
Which statement below concerning G proteins is true ?


>G proteins bound to Gdp are active

>Activation of a membrane receptor triggers an exchange of GDP for GTP on G -PROTEINS

> Adenylate cyclase activates G -proteins and causes dissociation into alpha and beta subunits

>cAMP activates G -Proteins ,leading to an exchange of GTP for GDP

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[Amreki]

>G proteins bound to Gdp are active

>Activation of a membrane receptor triggers an exchange of GDP for GTP on G -PROTEINS

> Adenylate cyclase activates G -proteins and causes dissociation into alpha and beta subunits

>cAMP activates G -Proteins ,leading to an exchange of GTP for GDP


I believe its the second answer choice. "Activation of a membrane receptor triggers an exchange of GDP for GTP on G proteins". After this activation of a G protein, it dissassociates into the alpha beta subunits and activates adenylate cyclase. This causes activation of cAMP which leads to protein kinase being activated. Thats my understanding of G proteins, however I'm still studying for part 1, dont take my word for it!

Any one else can correct me or clarify?