Lesson 5 - Types of Lipids and Transport
Student Performance Objectives1. List and state a major function for each of the following types of lipids: fatty acids, triglycerides, phospholipids, eicosanoids, and steroids. 2. List and state a major function for each of the following types of lipoproteins: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL).3. Explain two ways cholesterol can become oxidized.Lesson OutlineA. Types of lipids and their basic properties 1. Fatty acid (FA) - utilized for energy and stored in the form of triglycerides. Hydrophobic. 2. Triglyceride (TG) - 3 FA's + glycerol. Main storage form of lipid in human fatty tissue. Hydrophobic. 3. Phospholipids - start with a TG, remove a FA and substitute a phosphate - this is a molecule that is now hydrophilic at the phosphate group and still hydrophobic at the fatty acid portion of the molecule. Basis for membrane structure (see Unit 4, lesson 12). 4. Eicosanoids - fatty acid derivatives utilized to produce hormones helping to regulate blood pressure, blood clotting, and inflammatory processes. They go by such names as prostaglandins (PG's), thromboxanes (TX's), and leukotrienes (LT's). 5. Steroids - cholesterol and its derivatives including vitamin D, bile acids, sex hormones, and adrenal hormones including aldosterone and cortisol. For a review of lipid structures and a look at the cholesterol molecule, see this site and scroll to the bottom: B. Lipid transport throughout the body. 1. Lipoprotein particles - since the lipids are water-insoluble, they must be transported in the plasma (which is 90% water) in water-soluble lipoprotein particles. a. The chylomicrons are produced in the intestine to transport absorbed lipids to adipose tissue and the liver. See b. The VLDL and LDL particles are produced in the liver to transport liver- packaged lipids to the tissues (e.g., the liver synthesizes about 85% of the body's total cholesterol content.) c. The HDL particles return unutilized lipid to the liver for both re-utilization and excretion into the bile. d. There is no "good" and "bad" cholesterol in that all the transport forms of cholesterol have a function. e. When cholesterol is oxidized by the powdering of natural products (e.g., powdered eggs and powdered whole milk used in the baking industry) it becomes oxidized and potentially damaging to other cellular molecules. The free radicals introduced into the respiratory and digestive passages and into the blood by cigarette smoke can oxidize the native cholesterol produced by the body or absorbed from food. For the structure of oxidized cholesterol, see http://www.jlr.org/cgi/reprint/38/5/1014 - page 2.