And usually 95% of the proteoglycan by mass consists of glycosaminoglycans and only 5% consists of that protein component. Now, what exactly are the functions of proteoglycans. Well, proteoglycans, these protein, sugar, biomolecules have four important functions which I've listed on the board and the first two functions we're going to focus on in this lecture. So function number one is it acts as joint lubricants. Function number two, it basically functions in the structural components of tissues and that includes connective tissue, for instance, bone and cartilage. Number three it functions to bind cells to extracellular matrix.