Answer:
Protein hormones are generally primary messengers. Primary messengers are the hormones that directly bind to specific receptors on the cell membrane, leading to the activation of intracellular signaling pathways. In contrast, secondary messengers are small molecules that are generated inside the cell in response to the binding of primary messengers to their receptors. These secondary messengers then activate downstream signaling pathways.
Protein hormones, such as insulin and growth hormone, are typically large molecules that cannot cross the cell membrane. Therefore, they bind to specific receptors on the surface of the cell, which triggers intracellular signaling pathways that ultimately lead to the biological response. As such, protein hormones act as primary messengers.
Step-by-step explanation: