Proteoglycans are large molecules found in the extracellular matrix of tissues. They consist of a core protein and one or more glycosaminoglycan (GAG) chains, which are long, unbranched carbohydrates. These molecules play a crucial role in providing structural support, regulating cell behavior, and maintaining the hydration of tissues. In addition to their structural functions, proteoglycans are involved in cell signaling and can influence the activity of growth factors. They are important in various biological processes, including cartilage formation and wound healing. Abnormalities in proteoglycan function can lead to diseases such as osteoarthritis and certain cancers.