What types of molecules act as marker molecules on the outer surface of the plasma membrane?

Marker molecules on the outer surface of the plasma membrane are primarily represented by glycoproteins and glycolipids. These molecules are crucial in cell recognition and communication processes. Glycoproteins, which have carbohydrate chains attached to them, are involved in various cellular functions including signaling, immune response, and cell adhesion. Similarly, glycolipids, which are lipids with attached sugar groups, also play a significant role in cell recognition and signaling.

The presence of these marker molecules on the cell surface is key for the immune system to distinguish between self and foreign cells, facilitating the appropriate responses to pathogens. Additionally, they can serve as receptors for hormones and other signaling molecules, contributing to cellular interactions and responses to the environment. Thus, the primary function of glycoproteins and glycolipids as marker molecules is essential for maintaining the integrity and functionality of cells.