Why are glycolipids found on the extracellular, but not the cytoplasmic, surface of the plasma membrane?
(a) Plasma membrane flippases transport them from the cytosolic face.
(b) The enzymes that produce them are present only on the extracellular surface of the plasma membrane.
(c) The enzymes that add the sugar groups are confined to the inside of the endoplasmic reticulum and the Golgi apparatus.
(d) The oligosaccharides on glycolipids are cleaved off by enzymes found only in the cytosol.
(e) They flip spontaneously, after incorporation, due to the hydrophilic sugar head groups.
Answer: (c) The enzymes that add the sugar groups are confined to the inside of the endoplasmic reticulum and the Golgi apparatus.
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