What does "mosaic" in "cell membrane fluid mosiac model" refer to exactly?

In regards the the “fluid mosaic” model of the cell membrane;

The “fluid” part is relates to the fluidity of the phospholipids, but the “mosaic” explanation of the concept varies between it being the various kinds of proteins AND lipids within the membrane, or just the different types of proteins in the membrane.

So which explanation of the “mosaic” is more accurate?

The “mosaic” in the “fluid mosaic model” refers to the array of proteins embedded in the phospholipid bilayer of the cell membrane. The term “mosaic” is used because these proteins are not uniformly distributed - instead, they form a sort of pattern, much like tiles in a mosaic. The proteins can vary widely in structure, function, and distribution, contributing to the mosaic nature of the membrane.

However, it’s also important to note that the membrane isn’t composed solely of phospholipids and proteins. Other components like cholesterol and carbohydrates also play crucial roles. Cholesterol, for instance, intersperses among the fatty acid chains of the phospholipids and contributes to membrane fluidity and stability. Carbohydrates attached to the proteins (forming glycoproteins) or lipids (forming glycolipids) mainly exist on the extracellular side of the membrane and play roles in cell recognition and adhesion. So, in a broader sense, the “mosaic” could be said to include these other components as well.

In summary, while the primary elements referred to by the “mosaic” term are proteins, it’s not incorrect to extend the term to encompass the diversity of components in the membrane, including different types of lipids and carbohydrates, as they all contribute to the functional diversity of the membrane.