Why Would a Transverse Diffusion or Flip-Flop of Membrane Phospholipids

question 19

Multiple Choice

Why would a transverse diffusion or flip-flop of membrane phospholipids from one leaflet to the other be so rare?

• A)Flippases are enzymes which are transiently stable and expressed at low concentrations.
• B)For flip-flop to occur, it would be necessary for the hydrophilic head of a phospholipid to move through the hydrophobic part of the bilayer, an extremely unlikely event.
• C)For flip-flop to occur, it would be necessary for the hydrophobic head of a phospholipid to move through the hydrophilic part of the bilayer, an extremely unlikely event.
• D)Other membrane activities like flexing and lateral shift inhibit phospholipid flip-flop.