Here's why:
* Structure: While the phospholipid bilayer provides the basic structure, it's the proteins embedded within that give the membrane its specific shape and form.
* Transport: Proteins act as channels, pumps, and carriers to move substances across the membrane, controlling what enters and leaves the cell.
* Communication: Receptor proteins bind to signaling molecules, triggering intracellular responses and enabling communication between cells.
* Enzymatic Activity: Some proteins act as enzymes, catalyzing reactions that occur within the membrane or at its surface.
* Cell Recognition: Proteins like glycoproteins and glycolipids on the membrane surface act as markers for cell recognition and interaction.
While the phospholipid bilayer is crucial for the membrane's barrier function, proteins are the workhorses, carrying out the majority of the plasma membrane's diverse functions.
