Lipids: Chemistry and Identification
Lipids, or fats, oils and waxes, have many important functions. Lipids make up biological (cell) membranes.
Lipids cushion, protect and insulate internal organs. Lipids are the precursors for many hormones (help control
and regulate the body) and help transport vitamins. Lipids are an essential material in maintaining the durability
of the skin. And, lipids are often used as energy storage when excess energy (lipid or carbohydrate) is available.
Identifying Lipids Using Models
I. Glycerol- A Monomer of Lipids
Fat molecules are made up of two small “building blocks” or chemical molecule (monomers). These molecules
are called glycerol and fatty acids. Figure 8-1 shows the structural formula of glycerol.
1. What three chemical elements are present in glycerol? ____ ____ _____
2. What is the molecular formula for glycerol? (Add the number of atoms of each element and record the totals.)
C______H______O______
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Locate your model of glycerol, how can you tell glycerol from the other monomers at your station?
Discuss. (HINT: What “group” do the other monomers have on their ends?)
II. Fatty Acids- Monomers of Lipids
The second kind of molecule which is part of a fat is a fatty acid. Many different fatty acids exist, but all are
similar in several ways. Butyric acid, caproic acid, and lauric acid are examples of fatty acids. Figure 8-2 shows
the structural formulas for these three fatty acids.
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Examine the structural formulas for these three molecules.
3. What three chemical elements are present in fatty acids? ____ ____ _____
4. How many oxygen atoms are present in each fatty acid? _____
5. Other than the types of elements and amount of oxygen atoms, how are all three of these molecules similar?
(HINT: What “group” do they have on their ends) ______________________________________________
6. How are all three structures different? _________________________________________________________
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Locate your model of acetic acid, simplest fatty acid, acetic acid (CH3COOH). How do you know which
one is acetic acid? Discuss.
Locate your models of butyric acid and caproic acid. How can you tell them apart? Discuss.
III. Lipids (Fats, oils and waxes) - Polymers of Lipids
A lipid or fat molecule consists of 4 monomers chemically joined together. This polymer is made from one
glycerol molecule and three fatty acid molecules. A change in the type of fatty acids used to make a lipid results
in a different type of a fat molecule.
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Locate your model of glycerol, remove three –O-H ends from the glycerol molecule.
Locate your model of acetic acid, remove the –H off of the oxygen in the carboxyl group. Repeat for
your models of butyric and caporic acid.
Join the remainder of each of your three fatty acids to the exposed carbons on your glycerol model (the
locations from which the –O-H ends were removed.
Join the left over -O-H and –H ends from your models to each other.
7. What molecule did you form by joining the –O-H and the –H ends? ________ or _____________
8. How many molecules of water did you make as a byproduct of polymerizing your fat molecule? _____
Analysis
1. Name the types of molecules needed to form a fat molecule.
2. Are there any elements in glycerol that are not in carbohydrates?
3. List two ways that a fatty acid molecule differs from glycerol.
4. How many glycerol molecules are needed to form a fat molecule?
5. How many fatty acid molecules are needed to form a fat molecule?
6. Complete the following chart by using “yes” or “no” answers.
TABLE 8-3. SUMMARY OF GLYCEROL, FATTY ACIDS, AND AMINO ACIDS
GLYCEROL
FATTY ACIDS
AMINO ACIDS
Carbon present
Hydrogen present
Oxygen present
Nitrogen present
Monomers of proteins
Has a carboxyl group
Has an amino group
Molecules join to form fats
One molecule loses 3 OH ends