A group of polysaccharide-protein conjugates (joined together). Proteoglycans are found in the matrix of connective tissues and cartilage. The individual units are assembled in the form of a polypeptide backbone. to which glycosaminoglycans are covalently linked (attached). These aggregates resemble a test-tube bottle brush, and they function in adding to the "shock absorbing" quality of cartilage. They also attract water, and add to the cushioning effect.