Now, these are also known as transport membrane proteins because we find the proteins in the membrane and their function is to transport move these molecules across the two sides of the membrane. Now, we can categorize, we can break down these membrane proteins, transport membrane proteins into two types. We have membrane channels and we also have membrane pumps. So let's begin by focusing on membrane channels. So let's suppose we're going to focus on a specific type of ion. Let's say the sodium ion.