There was an uneven distribution of some types of lipids on the outer leaflet, while there were other types in the inner leaflet. In eukaryotic cells, we see certain trends with certain lipids. It is often found that SM, PG and PC are found in the outer leaflet, while PS, PI and PE are usually found in the inner leaflet (Verkleij et al. 1973). These lipids have similar characteristics, but also differ in various ways. This causes the asymmetric distribution of these molecules to have an effect on the behavior of cell membranes, including surface charge, membrane potential, shape, and permeability, to name a few. We know that the specific positions of these lipids have a reason for being there. For example, it has been shown that when PS, normally present on the inner monolayer, is exposed in mammalian cells, it constitutes a marker of apoptosis and a signal for elimination by macrophages (Marquardt et al..