Phospholipids Are Made by Integral ER Membrane Enzymes Whose Active

Multiple Choice

Phospholipids are made by integral ER membrane enzymes whose active sites face the cytosol and they are inserted into the outer (cytoplasmic) leaflet of the ER membrane. How then do lipids destined for the luminal leaflet of the ER membrane get there?

A) They diffuse freely into the luminal leaflet.
B) There are enzymes called flippases that flip these lipids into the opposite leaflet later.
C) They are disassembled on the cytoplasmic side and reassembled on the luminal side.
D) They move to the cytoplasmic leaflet by osmosis.
E) There are enzymes called translocases that flip these lipids into the opposite leaflet later.