They have many different functions. And one of the functions of calcium ions is it actually acts as a secondary messenger molecule in signal transduction pathway. So, for instance, as we discussed previously, when we examined the a phosphor nosetide signal transduction pathway, we saw that calcium played a very important role. It acted as a secondary messenger molecule. And the cell used the calcium to basically stimulate different types of proteins. The question is, what is it about calcium that actually makes these calcium ions such prevalent and good intracellular secondary messengers?