Glycoproteins and Glycolipids Are Identity Markers on the Cell SurfaceGlycoproteins and glycolipids are membrane molecules with carbohydrate chains that face the outside of the cell.They act mainly in cell recognition and the immune response.DefinitionSee other references1GlycoproteinA protein with carbohydrate chains attached, which are involved in cell recognition, signalling, and adhesion. Glycoproteins Are Carbohydrates Linked to ProteinsA glycoprotein is a protein with one or more carbohydrate chains attached.The protein sits embedded in the bilayer, and the carbohydrate chains point outward into the space around the cell.This outward position lets them handle cell-to-cell recognition and communication.NoteThe role of glycoproteins in cell-to-cell recognition is explored more in B1.1.7.Glycoproteins on red blood cells set your blood group, which is why donor and recipient blood must be matched before a transfusion.Glycolipids Are Carbohydrates Linked to LipidsA glycolipid is a lipid with a short carbohydrate chain of about one to four sugar units.The lipid part sits in the hydrophobic core of the membrane, and the carbohydrate chain points outward.They help with cell recognition, especially telling self cells apart from non-self cells.HintThis self recognition lets the immune system attack pathogens without harming healthy tissue.Together, glycolipids and glycoproteins act as identity markers used in blood typing, such as the ABO antigens, and in tissue recognition.The main markers matched for organ transplants are glycoproteins, the MHC or HLA molecules.The Glycocalyx Acts As a Protective BarrierGlycoproteins and glycolipids together form the glycocalyx, a carbohydrate-rich layer on the cell surface.It is prominent in animal cells, where it meets the outside environment.It acts as a protective barrier, cushioning the cell against mechanical and chemical damage.It also drives cell adhesion, helping cells stick together to form tissues.It supports immune defense by letting cells recognise harmful invaders.AnalogyThink of the glycocalyx as a Velcro layer for cells that helps them stick together and stay organised.Theory of KnowledgeHow does the immune system telling self from non-self relate to wider questions about identity?Could this biological process be compared to how humans form social or cultural identities?Active recallWhat is the difference in structure between a glycoprotein and a glycolipid?Why are the carbohydrate chains always on the extracellular side of the membrane?How do glycoproteins on red blood cells relate to blood transfusions?Name two functions of the glycocalyx.
