A Level Biology Practice Exam

What types of proteins are found in cell-surface membranes?

1. Structural proteins

2. Membrane proteins

3. Transport proteins

4. Both membrane and transport proteins

The correct answer is: Membrane proteins

Cell-surface membranes primarily contain membrane proteins, which play critical roles in various cellular functions. These proteins can take on several forms, including integral and peripheral proteins. Integral membrane proteins are embedded within the lipid bilayer and are essential for a range of functions such as facilitating communication between the cell and its environment, acting as receptors for signaling molecules, and supporting cell adhesion. Transport proteins, which are specifically involved in the movement of molecules across the membrane, are actually a subtype of membrane proteins. They help in transporting substances in and out of the cell, ensuring that essential nutrients can enter and waste products can exit. Therefore, while membrane proteins encompass a broader category that includes transport proteins, solely identifying cell-surface membranes with membrane proteins ensures recognition of their diverse functions. It highlights not just the transport aspect but also their roles in signaling and structural integrity. Thus, the assertion highlights the fundamental presence of membrane proteins in cell-surface membranes without restricting the context to just transport functions.