Which is the correct sequence of steps in G-protein coupled receptor signaling?

The correct sequence of steps in G-protein coupled receptor signaling starts with the binding of a neurotransmitter to its corresponding receptor on the surface of a cell. This binding is crucial because it activates the receptor and initiates the signaling cascade.

Once the neurotransmitter is bound to the receptor, the next step involves the activation of G-proteins. These proteins are typically heterotrimeric, consisting of three subunits (alpha, beta, and gamma). When the receptor is activated, it undergoes a conformational change that facilitates the exchange of GDP for GTP on the alpha subunit of the G-protein. This exchange is what activates the G-protein.

After the G-proteins are activated, they can then interact with various effector systems, such as adenylyl cyclase or phospholipase C. These effectors lead to the production of second messengers (like cAMP or IP3) that propagate the signal within the cell and result in various physiological responses.

Thus, the correct order of these events is: binding of neurotransmitter, activation of G-proteins, and then activation of effector systems. This sequence is foundational to understanding how G-protein coupled receptors (GPCRs) function