Name
Pd ______
CHEMISTRY OF FATS AND PROTEINS
All living things are composed of many different kinds of chemical molecules. Two very
imporant chemical molecules are fats and proteins. Both make up parts of living cells. Fats are a
part of all cellular membranes. They also may be stored within a cell as an energy source.
Proteins form part of almost all structures within a cell. Therefore, they are essential for cell
growth and repair. Also, many proteins are enzymes and are involved in cellular chemical
reactions.
In this investigation, you will
(a) Learn that all fat molecules are made up of two kinds of smaller molecules, glycerol
and fatty acids.
(b) Use structural formulas and models of glycerol and fatty acids to determine how
these molecules join together to form fat molecules.
(c) Learn that all protein molecules are made up of smaller molecules called amino
acids.
(d) Use structural formulas and models of amino acids to determine how these molecules
join together to form protein molecules.
Procedure
Part A. Fats
To better understand the chemistry of fats, it is helpful to study first the small molecules
which join to make up fats. Fat molecules are made up of two different kinds of chemical
molecules. These are glycerol and fatty acids.
Glycerol
Glycerol
Examine the structural formula of glycerol.
1. What elements are present in glycerol?
2. Are there any elements in glycerol that are not in carbohydrates?
___________________________
3. What is the molecular formula for glycerol? (Add the number of atoms of each
element and record the totals.)
C _____ H _____ O _____
4. As in carbohydrates, are there twice as many hydrogen atoms as oxygen atoms in
glycerol?________________________________
Fatty Acids
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 acids, and lauric acid are
examples of fatty acids.
Examine the structural formulas for the above three molecules.
5. What elements are present in all fatty acids? _________________________________
6. (a) What is the molecular formula for butyric fatty acid? C__H__O__
(b) What is the molecular formula for caproic fatty acid? C__H__O__
(c) What is the molecular formula for lauric fatty acid? C__H__O__
7. Are there twice as many hydrogen atoms as oxygen atoms in a fatty acid? _______________
8. What pattern appears in the fatty acid molecules regarding the number of oxygen atoms?
_______________________________
9. Note the end of butyric acid containing the oxygen atoms. This special end arrangement of
carbon, hydrogen, and oxygen is called a carboxyl group. Is the carboxyl group present in all
fatty acids shown? _________________________________
10. (a) List a similarity between glycerol and fatty acids. ________________________________
(b) Do fatty acids and glycerol both contain a carboxyl group? ________________________
Combining Glycerol and Fatty Acids to Form Fats
A fat molecule consists of one glycerol molecule and three fatty acid molecules joined together.
Cut out the glycerol and fatty acid paper model molecules. Cut along the solid lines only.
Attempt to construct a fat molecule.
11. Will the fat molecule fit together as pieces in a puzzle? ____________________________
Remove three OH ends from the glycerol molecule and three H ends from the fatty acids. Now
join the molecules to form a fat.
12. (a) How many glycerol molecules are needed to form a fat molecule? ________________
(b) How many fatty acid molecules are needed to form a fat molecule? _______________
Join the leftover H and OH ends from your models.
13. What chemical substance is formed when the H and OH ends are joined? ______________
Production of a fat molecule is a chemical reaction. A chemical shorthand way of expressing
the formation of a fat is as follows:
Glycerol + Fatty acid  Fat + Water
molecules
molecules
Glycerol + 3 fatty acids
(fat)
14. How many water molecules are formed when one fat molecule is produced? _____________
Many fats exist in living things. The wide variety of fats are formed by different combinations
of fatty acid molecules.
15. What molecule remains the same in fats? _______________________________
Part B. Proteins
Proteins are complex molecules made up of simpler building blocks or smaller molecules. The
small molecules which make up protein molecules are called amino acids.
Amino Acids
Examine the structural formulas of the four representative amino acids.
Glycine
Alanine
Threonine
16. The element nitrogen (N) is present in amino acids. Is nitrogen present in fats and
carbohydrates? (Use structural formulas as a guide.) _______________________________
17. (a) What is the molecular formula for the amino acid glycine? C_ H_ O_ N_
(b) What is the molecular formula for the amino acid alanine? C_ H_ O_ N_
(c) What is the molecular formula for the amino acid threonine? C_ H_ O_ N_
18. Are the molecular formulas for all amino acids the same? ____________
19. What end arrangement of atoms is present in amino acids that is also present in fatty acids?
________________________________
20. Another end arrangement in all amino acids consists of a nitrogen atom and two hydrogen
atoms. This group is called an amino group. Do structural formulas for all amino acids have
amino groups?____________
Combining Amino Acids to Form Protein
Protein is composed of many amino acids joined together chemically.
Cut out the four amino acid models from page 39. Cut along the solid lines only. Attempt to
join the amino acids. Will the protein molecule fit together? ________________
Join the molecules by removing as many OH groups and H groups as needed from the amino
acids. All four amino acid molecules can be joined in this manner to form a protein. Join them
in the order valine (val), threonine (thr), alanine (ala), and glycine (gly).
Rejoin the leftover OH and H ends.
21. What chemical substance is formed when the OH’s and H’s are joined?
Chemists express the joining of these amino acids as follows:
Val + Thr + Ala + Gly  Protein + Water
Valine
+
Threonine
+
Alanine
+
Glycine
22. How many molecules of water are formed when four amino acids join together? __________
Other combinations of amino acids result in the formation of different proteins.
Analysis
1. What two molecule types are needed to form a molecule of fat?
________________________________________________________________________
2. How many of each type of these molecules are needed to form a molecule of fat?
________________________________________________________________________
3. List one way fatty acids differ from glycerol.
________________________________________________________________________
4. What small molecule is needed to form a large protein molecule?
________________________________________________________________________
5. List one way amino acids differ from fatty acids.
_______________________________________________________________________
6. How might one protein differ from another?
_______________________________________________________________________
7. Complete the table with yes or no.
Glycerol
a) Carbon is present
b) Hydrogen is present
c) Oxygen is present
d) Nitrogen is present
e) Compound has twice the
amount of hydrogen as oxygen
f) Compound has a carboxyl
group
g) Compound has an amino group
h) Can join to form proteins
i) Can join to form fats
j) One molecule loses 3 OH ends
Fatty acids
Amino acids