Final answer:
The correct answer is option a. The membrane-bound GTP-binding proteins are known as trimeric GTP-binding proteins or heterotrimeric G-proteins. They play a crucial role in signal transduction by interacting with G-protein-coupled receptors and regulating cellular responses.
Step-by-step explanation:
The student is asking about the type of GTP-binding proteins that are membrane-bound. These membrane-bound proteins are involved in signal transduction and interact with the cell's membrane receptors to initiate a cellular response. Two main types of GTP-binding proteins are involved in these processes: trimeric GTP-binding proteins, also known as heterotrimeric G-proteins, and monomeric GTP-binding proteins, which include small GTPases like Ras and Rho. In the context of the question, which focuses on membrane-bound GTP-binding proteins, the correct answer is trimeric GTP-binding proteins.
These proteins, also referred to as G-proteins, are vital for numerous cellular functions including signal transduction. When a signaling molecule like a hormone binds to a G-protein-coupled receptor (GPCR) in the plasma membrane, the GDP molecule associated with the alpha (α) subunit of the G-protein is exchanged for GTP, causing the beta (ß) and gamma (γ) subunits to dissociate. This exchange initiates various cellular responses. Notably, stimulatory G-proteins are designated Gs, while inhibitory G-proteins are designated Gi.
In conclusion, the type of GTP-binding proteins that are membrane-bound are the trimeric GTP-binding proteins. This is option (a) in the multiple-choice question the student has presented.