Describe the role of signal molecules in activating gene expression at the appropriate time

Some genes only need to be expressed or produced when needed. For example, fibrinogen is a protein that needs to be produced when a person needs to clot. A signal protein 'signals' or tells the DNA to start producing that particular protein. Imagine if the protein was produced all of the time at the same quantities...a person would be prone to strokes and other sicknesses that are caused by blocking the flow of blood to tissue.

I’d say a : water molecules