Do cell membranes have more phospholipids in one layer than in the other?

Question

Assuming the cell membrane to have a spherical shape, geometry tells us that the area of the inner leaflet is smaller than the area of the outer due to the difference in radius between them. Does this mean that the inner layer has fewer phosholipids? And, if so, how does it affect the fluidity relation between the layers?

Answer 1

Cells come in various different shapes and sizes. For example epithelial cells can be squamous (flattened), cuboidal, columnar etc.. Other types of cells like Red blood cells are in a biconcave shape, so majority of cells are not in a perfect sphere.

The composition of the inner leaflet and outer leaflet do not differ in the amount of phospholipids however there types of phospholipids do in fact differ. Phospholipids can be phoshoptidy serine (PS), phosphotidyl ethanolamine (PE), phosphatidyl choline (PC), or phosphatidyl inositol (PI).

PS, PE, and PI are all majority found on the inner leaflet of the phospholipid bilayer, whereas PC is found on the outer leaflet of the cell membranee.