Which extracellular macromolecules are adhesion molecules?

• A. Glycoproteins
• B. Proteoglycans
• C. Collagen
• D. Elastin

Answer: (A)

Glycoproteins serve as adhesion molecules in the extracellular space. They carry carbohydrate groups and provide binding sites for cell-surface receptors such as integrins, as well as for other matrix components. In the extracellular matrix, glycoproteins like fibronectin and laminin form bridges that connect cells to each other and to the matrix, supporting attachment, signaling, and organized tissue structure. This adhesion role is distinct from the other options: collagen and elastin are structural proteins giving tensile strength and elasticity, while proteoglycans create a hydrated gel that fills space and modulates diffusion rather than primarily mediating cell–matrix adhesion. Hence, glycoproteins are the extracellular macromolecules most involved in adhesion.