Question

9. Phosphatidylserine is only found on the interior leaflet of healthy eukaryotic cells. Proteins in the cell actively maintain this state. Why is it necessary to have processes to bring PS to the interior? What happens when this does not happen? Why do cells maintain PS on the interior of the cell?

Answer 1

Phosphatidylserine is a type of phospholipid, that is active at cell membranes and is the building block of the cell membranes. Phospholipids are fat soluble substances that are found as structural components within the cell membrane of every cell in the human body. They make up the outer membrane which surrounds every cell in our body, separating the interior of the cell from the exterior.

Phosphatidylserine distribution in the cell membrane is localized to the inner (cytoplasmic) leaflet. Exceptions include when the cell is damaged PS exposure on the outer leaflet starts the blood clotting process or in apoptosis. Otherwise, the negatively charged phospholipids are in the inner leaflet. Apoptotic cells lose the asymmetric distribution of phospholipids in their plasma membrane. As a consequence, negatively charged phosphatidylserine, which is normally confined to the cytosolic leaflet of the lipid bilayer, is now exposed on the outside of the cell, and initiates the phagocytosis of the dead cell.