Final answer:
Glycoproteins are molecules found in human cells composed of proteins bonded to carbohydrates, contributing to cell recognition and immunity, and are key components of the cell membrane glycocalyx.
Step-by-step explanation:
A glycoprotein is a complex molecule composed of a protein and carbohydrate chains. Specifically, it refers to a protein that has carbohydrate molecules attached, which extend into the extracellular matrix, playing important roles in cellular functions such as cell recognition. Glycoproteins are found in various parts of human cells, notably as integral membrane proteins, where they contribute to the formation of the glycocalyx - a fuzzy coating around the cell that is involved in cell-to-cell interactions, signaling, and immune response. For instance, glycoprotein antigens on red blood cells determine blood groups such as A, B, AB, O, and Rh, and they help differentiate self from non-self cells to avoid immune attacks.
These molecules extend from both membrane proteins and some membrane lipids, and collectively contribute to the glycocalyx. This external cellular feature is crucial for various biological processes including hormone reception, nutrient breakdown, and cell adhesion. Glycoproteins hold a significant place within the immune system, where immunoglobulins (antibodies) function as glycoproteins that identify and neutralize foreign substances. Cells recognize each other and signal accordingly, in part, due to the unique glycoprotein structures on their surfaces.