Final answer:
Second messengers are typically small molecules, not large, and their ability to elicit different responses in various cell types is due to the unique combination of enzymes and target proteins present in each cell. cAMP and Ca2+ are examples of second messengers that can activate different pathways depending on the cell-specific context.
Step-by-step explanation:
The statement that "Second Messengers must be large and easily diffusable" is false. Second messengers are typically small molecules that can rapidly diffuse through the cytoplasm, facilitating quick signal propagation within cells. The same second messengers being used in different cells but triggering different responses is possible due to the specific cellular context. This context includes the presence of different enzymes, such as A-kinase, and various target proteins within each cell type. Similar second messengers like cyclic AMP (cAMP) and calcium ions (Ca2+) can therefore have diverse effects based on the specific cellular components they interact with. Cells contain unique sets of proteins that these second messengers may regulate, leading to different cellular responses, despite the messengers themselves being the same. Additionally, the location where a second messenger is released can influence the response, contributing to the complexity of intracellular signaling and the concept of 'crosstalk' among multiple signaling pathways.