Which component contributes to the structure of cell membranes besides phospholipids?

Proteins play a crucial role in the structure and function of cell membranes in addition to phospholipids. In biological membranes, proteins are interspersed throughout the phospholipid bilayer, where they can either span the membrane (integral proteins) or be loosely attached to the surface (peripheral proteins).

These membrane proteins serve various functions, including acting as channels or transporters for molecules to cross the membrane, serving as receptors for signaling molecules, and playing a role in cell recognition and communication. The presence of proteins contributes to the fluid mosaic model of the cell membrane, where lipids and proteins are arranged in a dynamic and flexible manner, allowing for functional versatility and adaptability.

In contrast, while nucleotides, carbohydrates, and water are important for cellular function, they do not contribute directly to the structural integrity of the cell membrane in the way proteins and phospholipids do. Nucleotides are primarily involved in energy transfer and genetic material, carbohydrates are generally associated with cell recognition and signaling rather than membrane structure, and water is a solvent and medium for reactions but does not form part of the membrane's structural components.