Question

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

Answer 1

a. The enzymes that add the sugar groups are confined to the inside of the endoplasmic reticulum and the Golgi apparatus.

Step-by-step explanation:

Glycolipids are lipid molecules with attached carbohydrate groups, and they play important roles in cell recognition and signaling. The process of glycolipid synthesis occurs within the endoplasmic reticulum and the Golgi apparatus, where specific enzymes catalyze the addition of sugar groups to the lipid molecules. These enzymes are localized within these intracellular compartments and are not present on the cytoplasmic surface of the plasma membrane.

As a result, during the synthesis and assembly of glycolipids, the sugar groups are added on the luminal side of the endoplasmic reticulum and Golgi apparatus. The glycolipids are then transported and incorporated into the extracellular face of the plasma membrane. The enzymes responsible for adding the sugar groups are not present on the cytoplasmic side, which is why glycolipids are found exclusively on the extracellular surface of the plasma membrane.

Therefore, option a is the correct answer as it explains that the enzymes responsible for adding the sugar groups to glycolipids are confined to the inside of the endoplasmic reticulum and the Golgi apparatus.

hope this helps :)