There was a non-uniform 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. SM, PG, and PC are often seen to be 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 cell membrane behaviors including surface charge, membrane potential, shape, and permeability, to name a few. It is known that the specific locations of these lipids have a reason to be there. For example, it has been shown that when PS, normally present on the inner monolayer, is exposed in mammalian cells, it is a marker of apoptosis and a signal for disposal by macrophages (Marquardt et al..