And for this particular one, we have the amino group and we have this sulfate group. Now generally speaking, these glycosaminoglycans don't exist by themselves inside our body. Usually the glycosaminoglycans actually covalently associate with proteins to form a category of modified proteins known as proteoglycans. So what exactly is a proteoglycan? Well, a proteoglycan is basically a protein molecule that has attached to some type of glycosaminoglycan or many glycosaminoglycans. In fact, usually the glycosaminoglycan is the predominant component of the proteoglycan.