Lesson 4 - The Lipids - Introduction, Functions, and Demonstration
Student Performance Objectives
1. Define hydrophobic and hydrophilic.
2. Draw a schematic diagram of a triglyceride showing glycerol and three fatty acids.
3. Compare the energy storage by triglycerides compared with carbohydrates and proteins.
4. Explain the similarities and differences between fats and oils.
5. Define saturated, monounsaturated and polyunsaturated with regard to fatty acids.
6. Explain how the natural products, olive oil and corn oil, are referred to as monounsaturated or
7. Describe 5 functions for lipids in the human body.
A. Definitions and general information
1. For a good general introduction to the lipids with a description and showing structures,
2. Hydrophobic in general - critical in construction of cellular membranes separating
fluid compartments inside and outside cells, and inside and outside organelles.
Distinguish hydrophobic from hydrophilic. Definition of hydrophobic:
Definition of hydrophilic:
For an animated view of the relationship of lipids and water, see
3. Examples: natural substances like vegetable oils, butter, and lard are mostly triglycerides.
To understand a triglyceride, start with the idea of a fatty acid:
Structure of a fatty acid:
If desired, the naming of the alpha and omega carbon atoms in a fatty acid may be observed at:
Generalized triglyceride structure:
4. Triglycerides are energy dense (9 kcal/gram) - useful for energy storage. Note -
carbohydrates and proteins, when burned for energy, yield 4 kcal/gram.
5. Fats are triglycerides that are solid at room temperature; oils are triglycerides that are liquid at room
a. Triglycerides are the combination of a glycerol molecule and 3 fatty acids.
b. The fatty acids may be saturated, monounsaturated or polyunsaturated.
6. Being solid or liquid at a given temperature depends on the degree of saturation of the
fatty acids composing the triglycerides of the given substance. A monounsaturated
vegetable oil like olive is liquid at room temperature. A polyunsaturated oil like
safflower remains as a liquid even in the refrigerator, where the olive oil solidifies. A
saturated fat like lard or butter is solid at room temperature and becomes harder in
texture in the refrigerator.
7. One double bond in the carbon chain of a fatty acid makes the molecule monounsaturated. Two or
more double bonds in the fatty acid's carbon chain makes
the molecule polyunsaturated. No double bonds in the carbon chain of a fatty acid
makes the molecule saturated.
B. Functions of lipids in the human body.
2. Cushioning - our soft internal organs need protection from our endoskeleton.
3. Cell membranes - utilize phospholipids and cholesterol in their structure.
a. Concept of the amphiphilic molecule - one end hydrophobic; the other end
b. Phospholipids are made by removing one fatty acid from a triglyceride and
substituting a phosphate group which is hydrophilic. Structure of a phospholipid:
c. To observe the placement of phospholipid molecules composing cellular
4. Hormone production
a. Steroid hormones like estrogens and androgens.
b. Eicosanoids like the prostaglandins, leukotrienes and thromboxanes.
5. Heat generation (brown fat). Seen extensively in newborn babies.
6. Energy storage.
7. Appetite satiety and food flavour and texture enhancement.
C. DEMONSTRATION: lipid characteristics. Compare coconut oil, butter, olive oil and safflower oil.
Note that the coconut oil is solid at room temperature (~ 70º F) as is butter (although it is soft).
Note that olive oil is solid at refrigerator temperatures (~ 40º F) but liquid at room temperature, and
that safflower oil is liquid at both refrigerator and room temperatures. All of these physical
observations are based on the degree of saturation of the lipids being observed.
(These effects are also due, in part, to the chain length of the fatty acids, particularly in the coconut oil
which contains relatively short chain length fatty acids).