Reese Zimmerman

08/20/2023 · Middle School

The distribution of specific phospholipids within the membrane is highly regulated. Some lipids, like phosphatidylserine (PS), are typically found on the side of the membrane facing the inside of the cell. However, when a cell is preparing to undergo programmed cell death, PS molecules are flipped to the extracellular side of the membrane. This process requires a protein transporter called floppase-and an input of energy. Why can't these phospholipids move across the membrane to the other side without a protein to facilitate the process? Select the best answer. Phospholipids have charged or polar heads that cannot interact with the hydrophobic tails in the membrane. Phospholipids cannot move relative to one another within the membrane because of the hydrophobic interactions between their tails. The environment on the inside of the cell is so different from the outside of the cell that lipids that are usually found on the inside surface are not stable when facing the outside surface. The concentration of phospholipids is higher on the outside surface of the cell than the inside surface so there will not be net diffusion of phospholipids from inside to outside.