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Lesson 5 - Types of Lipids and Transport

Student Performance Objectives
1. 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 Outline
A. Types of lipids and their basic properties
    1. Fatty acid (FA) - utilized for energy and stored in the form of triglycerides.
    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
    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
    - page 2.