And so in this lecture, what I'd like to focus on is discuss how different types of abnormalities in a signal transduction pathway can actually lead to cancer. Now, before we actually begin our discussion on the abnormality part, let's focus on how normal process takes place and how normally our cells terminate these signal transduction pathways. And to use an example, we're going to focus on the EGF signal transduction pathway where EGF stands for Epidermal growth factor. Remember, this is the pathway used by the cells that ultimately stimulates the growth and division of epithelial and epidermal cells. So let's begin by focusing on how this pathway actually takes place, beginning with the binding of the EGF molecules onto their domains. So we have two EGF molecules bind onto each one of these domains shown in purple.