Lipids, such as fats and waxes, that have attached carbohydrate groups called glycans are referred to as glycolipids. There are many different kinds of glycolipids that serve many different biological roles; primarily, though, they are involved with cellular recognition and energy production. Glycans most commonly bond to phospholipids, which have one water-soluble end and one water-insoluble end. They are commonly found as parts of cellular membranes because of some traits related to their polar and nonpolar ends. Generally speaking, a glycolipid will form when a carbohydrate chain is attached to the outer part of a cellular membrane that is composed of lipids.
The most common types of glycolipids are glycosphingolipids, which are made up of ceramides connected to a glycan. Ceramides are made up of fatty acids connected to sphingosines, which are simply amino alcohols that are commonly found in nerve tissue. Glycosphingolipids tend to serve many roles relating to nerve and brain function; they are related to the proper functioning of myelin sheaths around nerves and of various signaling processes across cellular membranes. Some larger glycosphingolipids are actually related to the antigens that define blood type and can help mark the presence of some tumors. Glycosphingolipids are very important kinds of glycolipids; they appear in many different forms and are involved in many different biological processes.
Galactolipids are another group of glycolipids; they are defined by their carbohydrate group, galactose. While glycosphingolipids tend to have nitrogen atoms somewhere in their molecular structures, galactolipids do not. Galactolipids are common in plants; they often replace some phospholipids in plants to allow phosphorus, which can be scarce, to be used for other important processes. Galactocerebroside is a type of galactolipid that is commonly found in the myelin sheath around the nerves of vertebrates. Most other forms of galactolipids are only found in plants.
Niemann Pick disease Type C is a genetic disorder that is related to the storage of some forms of lipids, including some glycolipids. Specifically, it occurs when lysosomes, which are organelles that contain enzymes involved in digestion, are unable to properly break down glycolipids and cholesterol. As a result, these substances build up within the lysosomes and cause many problems. Niemann Pick disease Type C can present a very wide variety of symptoms, making it very difficult to diagnose properly. Neurological degradation is the most common symptom; individuals with Niemann Pick disease Type C often find it difficult to walk properly, swallow, sleep properly, or engage in a wide variety of previously-simple activities. In many cases, the disease eventually kills the afflicted individual.