The Glycolipids are located mainly in the plasma membrane and they are found only in the noncytosolic half of the bilayer. Their sugar groups therefore are exposed on the exterior of the cell where they form part of the protective coat of carbohydrate that surrounds most animal cells. This protective coat is the glycocalyx. Glycolipid molecules acquire their sugar groups in the Golgi apparatus.
Enzymes that add the sugar groups are confined to the inside of the Golgi apparatus so that the sugars are added to lipid molecules in the non cytosolic half of the lipid bilayer. Once a glycolipid molecule has been created in this way it remains trapped in this monolayer. as there are no flippases to transfer the glycolipid to the cytosolic side of the membrane.
There are Two broad types of glycolipids can be distinguished,
1. Glycerol Based
Enzymes that add the sugar groups are confined to the inside of the Golgi apparatus so that the sugars are added to lipid molecules in the non cytosolic half of the lipid bilayer. Once a glycolipid molecule has been created in this way it remains trapped in this monolayer. as there are no flippases to transfer the glycolipid to the cytosolic side of the membrane.
There are Two broad types of glycolipids can be distinguished,
1. Glycerol Based
- Fatty acid chains attached to the glycerol molecule.
- A carbohydrate group linked to the 3rd carbon of glycerol with no bridging phosphate group
- Glycerol based glycolipids are the primary form in plants and bacteria
2. Sphingolipid Based
- These are based on the addition of carbohydrate units to the sphingolipid nucleus This type of glycolipid is the main form in animal cell membranes
- Simple glycolipids formed by the addition of a single sugar unit are called cerebrosides
- Addition of straight or branched sugar chains producesgangliosides. Carbohydrates added can be have considerablevariation in structure
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