By: Halie Derr Nick Splitt Complex Lipids 13.4-13.8 By: Halie Derr Nick Splitt

What are complex lipids? Complex lipids help to create the main components of membranes. Complex lipids are also referred to as compound lipids. They can be classified into two groups: phospholipids and glycolipids.

What are phospholipids? (continued) Phospholipids contain at least one fatty acid, a phosphate group, and sometimes a nitrogenous base. Two subtypes of phospholipids are glycerophospholipids and sphingolipids. They are one of the most important components of a membrane. Most phospholipids are created in the liver and enter the bloodstream.

What are glycerophospholipids? Their structures are similar to that of fats. They are membrane components of cells distributed throughout the body. They contain glycerol as the alcohol Also, carbon 2 of the glycerol is always unsaturated. They can be broken down into three groups which are esterified by either a fatty acid or a phosphate group which is esterified by another alcohol.

What are glycerophospholipids? (continued) If the alcohol choline is used phosphatidylcholines (lechtin) is created. Lechtin usually contains linoleic acid in the middle and stearic acid on the end. Lechtin is a major component of egg yolk, a good emulsifier, and found in mayonnaise. If an alcohol such as ethanolamine or serine is used it will create cephalins which are very similar to lechtins.

What are glycerophospholipids? (continued) When the alcohol inositol is bonded to a molecule by a phosphate ester bond Phosphatidylinositols (PI) is created. They can be found in biological membranes and can be used as signaling molecules for chemical communication.

(Purple indicates the different alcohols)

What are sphingolipids? Johann Thudichum discovered sphingolipids in 1874 and named them after the Sphinx. When hydrolyzed, sphingosine substitutes for glycerol in these lipids. They are common membrane components because they have both hydrophilic and hydrophobic characteristics. Ceramide is a combination of a fatty acid and sphingosine. Ceramides are found in sphingolipids.

How do sphingomyelins help in the myelin sheath? Myelin sheaths, the coating of nerve axons in the brain, contain different complex lipids, one of them being sphingomyelins. Sphingomyelins are the most important lipids in the myelin sheaths of nerve cells. They are associated with diseases such as multiple sclerosis.

What are glycolipids? Glycolipids are complex lipids that contain carbohydrates and ceramides There are several different groups of glycolipids, such as gangliosides and cerebrosides Gangliosides have a more complex carbohydrate structure Cerebrosides contain mono- or oligosaccharides. They occur mainly in the brain, accounting for 70% of the brains dry weight and at nerve synapses. The fatty acid of the ceramide part of the cerebroside contains 18 to 24 carbon chains.

What are membranes? Made up of lipid bilayers A lipid bilayer is a two-layered structure of complex lipids set tail to tail. Hydrophobic tails point towards each other Hydrophilic heads point out from each other enabling them to be close to water. Membranes have liquid like characteristics because the unsaturated fatty acids prevent tight packing in the lipid bilayer. An important component of a membrane is cholesterol. Cholesterol has a similar structure to other membranes

What role do lipids play in the structure of membranes? Complex lipids form membranes around organelles which are small structures inside the cells. They provide selective transport for nutrient and waste products into and out of cells. In addition, they separate cells from their external environment. An important component of complex lipids are the unsaturated fatty acids especially in the lipid bilayer.