When G proteins are activated by hormones, they trigger a cascade of events that ultimately lead to the production of second messengers. These second messengers are small molecules that relay signals from the hormone-activated G protein to downstream targets within the cell.

Here's a breakdown:

1. Hormone binds to receptor: A hormone, like epinephrine or glucagon, binds to its specific receptor on the cell membrane.

2. Receptor activates G protein: This binding activates the associated G protein, causing it to exchange GDP for GTP.

3. G protein activates effector enzyme: The activated G protein then interacts with an effector enzyme, typically either adenylate cyclase or phospholipase C.

4. Effector enzyme produces second messenger:

* Adenylate cyclase produces cyclic AMP (cAMP).

* Phospholipase C produces inositol triphosphate (IP3) and diacylglycerol (DAG).

These second messengers then go on to activate various intracellular pathways, ultimately leading to a specific cellular response.

Examples of cellular responses triggered by second messengers:

* cAMP: Activates protein kinase A (PKA), which phosphorylates proteins involved in various processes like glycogen breakdown, muscle contraction, and gene transcription.

* IP3: Binds to receptors on the endoplasmic reticulum, leading to the release of calcium ions.

* DAG: Activates protein kinase C (PKC), which phosphorylates various proteins involved in cell growth, differentiation, and other processes.

In summary, the activation of G proteins by hormones leads to the production of second messengers, which then act as intracellular signaling molecules to mediate a wide range of cellular responses.