The correct response centers on the role of second messengers in cellular signaling, particularly in relation to plasma membrane receptors. Cyclic AMP (cAMP) is a well-known second messenger that is crucial for many signal transduction pathways. It is synthesized from ATP by the enzyme adenylate cyclase, which is activated by G protein-coupled receptors. Once produced, cAMP activates protein kinase A (PKA), leading to various physiological responses.
MAP kinase, or mitogen-activated protein kinase, is part of a signaling cascade that is often triggered by receptor activation, especially in the context of growth factor signaling. While MAP kinases are involved in transducing signals, they are not classified as second messengers in the same way that cAMP is.
The correct pairing of cyclic AMP, a classic second messenger, and MAP kinase underscores the understanding of cellular signal transduction processes, linking extracellular signals to intracellular responses.
In contrast, the other options either combine second messengers with elements that do not function in the same category or confuse different aspects of the signaling pathways, making them less applicable for this question. For instance, NADH is primarily involved in metabolic pathways rather than in directly mediating signal transduction from receptors, while calcium