Final answer:
Extracellular glycoproteins made up of three polypeptide chains linked by disulfide bonds are known as collagen, which are integral in cell-cell recognition, structural support, and are part of the extracellular matrix and glycocalyx.
Step-by-step explanation:
Extracellular glycoproteins consisting of three polypeptide chains linked by disulfide bonds are known as collagen. Collagen is a major component of the extracellular matrix (ECM) and plays an essential role in providing structural support to cells and tissues. These glycoproteins are characterized by their unique triple helix structure formed by the three polypeptide chains. The chains are often glycosylated, which means they have carbohydrate molecules attached to specific amino acids through a process called glycosylation. Glycosylation occurs in the rough endoplasmic reticulum and the Golgi apparatus, where sugars are added to the protein.
These glycoproteins play numerous roles in cell-cell recognition, acting as labels that identify and differentiate cells. They are integral in interactions with other cells and the ECM components, aiding in cell adhesion, migration, and signaling. They are also integral membrane proteins that are part of the glycocalyx, which is a carbohydrate-rich area that envelops the outside of the cell membrane.
Furthermore, glycoproteins, including those forming collagen, are involved in various physiological processes and are crucial for maintaining the health and integrity of connective tissues. Defects in glycosylation can lead to several human health issues, underlying the importance of these glycoproteins in biology and medicine.