Question

multiple choice 1 point
in order for a g protein signaling to be active:
the receptor must activate transcription in the nucleus
a (alpha) subunit must bind gtp
the β (beta) and y (gamma) subunits must have kinase activity
protein kinase a (pka) must first bind to camp

Explanation:

• G - protein signaling: When a ligand binds to a G - protein - coupled receptor (GPCR), it causes a conformational change in the receptor. This change leads to the activation of the G - protein.
• G - protein structure: A G - protein is a heterotrimer consisting of α, β, and γ subunits. In the inactive state, the α subunit is bound to GDP.
• Activation mechanism: Upon receptor activation, the GDP on the α subunit is exchanged for GTP. Once the α subunit binds GTP, it dissociates from the β - γ complex. The GTP - bound α subunit (and the free β - γ complex in some cases) can then go on to activate downstream effectors.
• Analyzing options:
• The receptor does not directly activate transcription in the nucleus in the context of G - protein activation. Transcription activation is usually a downstream event after multiple signaling steps.
• The β and γ subunits do not have kinase activity as a part of the basic G - protein activation mechanism.
• Protein kinase A (PKA) binding to cAMP is a downstream event in some G - protein - mediated pathways (e.g., those that increase cAMP levels), not a requirement for G - protein activation itself.

Answer:

α (alpha) subunit must bind GTP