Notes to Instructors
Chapter 4 Carbon and the Molecular Diversity of Life
Chapter 5 The Structure and Function of Macromolecules
What is the focus of these activities?
The activities associated with Chapters 2 and 3 provided students with a review of some of
the basics of inorganic chemistry. The activities associated with Chapters 4 and 5 deal with
What are the particular activities designed to do?
Activity 4.1/5.1 How can you identify organic macromolecules?
This activity is designed to help students easily recognize carbohydrates, lipids, proteins,
Activity 4.2/5.2 What predictions can you make about the behavior of organic
macromolecules if you know their structure?
In this activity, students examine the general properties of organic macromolecules. In
particular, they examine the properties of functional groups and how these can modify the
Notes to Instructors 11
What misconceptions or difficulties can these activities reveal?
Activity 4.1/5.1
Question 1, Part A: This question asks for the C:H:O ratio of the various
macromolecules. For carbohydrates, it is approximately 1:2:1. For many lipids, it is
approximately 1:2:very few. And for proteins and nucleic acids, there is no reliable ratio
of C:H:O. Many students become upset that the answer for proteins and nucleic acids is
Activity 4.2/5.2
Question 1: The table asks students to look at different possible characteristics of R
groups.
12 Notes to Instructors
This question helps students understand, for example, that something that is polar is also
hydrophilic; that is, these designations are not mutually exclusive. In addition, by
learning the characteristics of key functional groups, students will have a better
understanding of how modifications in macromolecular structure can lead to
modifications in function.
R group Basic, acidic, or
neutral
Polar or nonpolar Hydrophilic or
hydrophobic
Answers
Activity 4.1/5.1 How can you identify organic macromolecules?
Refer to the figure (Some Simple Chemistry) on the next page when doing this activity.
Part A. Answer the questions. Then use your answers to develop simple rules for
identifying carbohydrates, lipids, proteins, and nucleic acids.
1. What is the approximate C:H:O ratio in each of the following types of
macromolecules?
Activity 4.1/5.1 13
Carbohydrates
1:2:1
Lipids
1:2:very few
Proteins
There is no reliable
Nucleic acids
There is no reliable
2. Which of the compounds listed in question 1 can often be composed of C, H, and O
alone?
3. Which of the compounds can be identified by looking at the C:H:O ratios alone?
4. What other elements are commonly associated with each of these four types of
macromolecules?
Carbohydrates Lipids Proteins Nucleic acids
Always contain P No No (except for
phospholipids)
No Yes
does not contain P (for example) the answer to “Generally contain no P” would be yes.
14 Activity 4.1/5.1
CH
2
OH
H
OH
OH
CO
CC
CC
OH
HH
H
HO
H
HO
H
Proteins:
Enzymes,
structural
proteins
Sugars, starches,
glycogen,
cellulose
Carbohydrates:
Compound
Some Simple Chemistry
Basic
components Reaction
Product
Disaccharide6C hexose
amino
group carboxyl
group
R
H
C COOHH
2
N
R
HH
H
OH
O
CCH
2
N
O
R
HOH
CCN
dehydration
reaction
dehydration
reaction
+ 1 H
2
O
Dipeptide
+ 1 H
2
O
H2O
CH
2
OH
H
OH
CO
CC
CC
CH
2
OH
CO
CC
CC
CH
2
OH
HH
O
O
CH
2
OH
O
H
2
O
peptide
bond
R
H
CH
2
N
O
C
R
H
O
OH
CCN
H
Amino acid
5. Functional groups can modify the properties of organic molecules. In the following
table, indicate whether each functional group is polar or nonpolar and hydrophobic
or hydrophilic. Which of these functional groups are found in proteins and lipids?
Activity 4.1/5.1 15
Functional
group
Polar or
nonpolar
Hydrophobic
or hydrophilic
Found in all
proteins
Found in
many proteins
Found in
many lipids
—OH Polar Hydrophilic No In some R
groups
In fatty acids
as terminal
reactive group
6. You want to use a radioactive tracer that will label only the protein in an RNA virus.
Assume the virus is composed of only a protein coat and an RNA core. Which of the
following would you use? Be sure to explain your answer.
a. Radioactive P b. Radioactive N c. Radioactive S d. Radioactive C
To distinguish between protein and RNA in a virus, you could use radioactively
7. Closely related macromolecules often have many characteristics in common. For
example, they share many of the same chemical elements and functional groups.
Therefore, to separate or distinguish closely related macromolecules, you need to
determine how they differ and then target or label that difference.
a. What makes RNA different from DNA?
RNA contains ribose sugar, whereas DNA contains deoxyribose sugar. In addition,
b. If you wanted to use a radioactive or fluorescent tag to label only the RNA in a cell
and not the DNA, what compound(s) could you label that is/are specific for RNA?
c. If you wanted to label only the DNA, what compound(s) could you label?
8. Based on your answers to questions 1–7, what simple rule(s) can you use to identify
the following macromolecules?
16 Activity 4.1/5.1
Carbohydrates Look for a 1:2:1 C:H:O ratio. Many carbohydrates will contain no
P, N, or S.
Part B. Carbohydrate, lipid, protein, or nucleic acid? Name that structure!
Based on the rules you developed in Part A, identify the compounds below (and on the
following page) as carbohydrates, lipids, amino acids, polypeptides, or nucleic acids. In
addition, indicate whether each is likely to be polar or nonpolar, hydrophilic or hydrophobic.
2) H
3
N
C
C
CH
2
C
N
O–
H O
H
CH
+
H
O
H
O
1) lipid (fat or triglyceride)
3) a tripeptide made up of
3 amino acids
The R groups are
hydrophobic with the
Activity 4.1/5.1 17
4)
O
CH
2
Base
H
–O
O–
P
O
O
–O
O
P
O
O
H
H
H
H
O
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
CH
2
C
OH
)6
H
3
C
)7
O
O
CH
2
H
H
N
OH OH
HH
HO PO
OH
C NH CH
2
CH
2
CH
2
CH
8)
NH
2
NH
2
+
NH
3
+
C
O–
O
9)
O
O
CH
2
OH
OH
HO
O
O
CH
2
OH
OH
O
O
CH
2
OH
OH
O
CH
2
OH
OH
OH
OH OH OH OH
H
H
CC
OH
H
C
OH
H
C
OH
H
C
OH
10)
O
H
5)
O
HOCH
2
CH
2
O
H
H
H
OH
HO
H
HO
HH
O
O
CH
2
OH
H
H
OH
OH H
4) single strand of 4 bases in DNA
5) disaccharide sugar or carbohydrate
A student, Mary, is given four samples and told they are lysine (an amino acid),
lactose (a disaccharide), insulin (a protein hormone), and RNA. The samples are in test
tubes marked 1, 2, 3, and 4, but Mary doesn’t know which compound is in which tube.
She is instructed to identify the contents of each tube.
a. In her first test, she tries to hydrolyze a portion of the contents of each tube.
Hydrolysis occurs in all tubes except tube 3.
b. In Mary’s next test, she finds that tubes 1, 2, and 3 are positive for nitrogen but only
tube 2 gives a positive result for the presence of sulfur.
c. The last test Mary performs shows that the compound in tube 1 contains a high
percentage of phosphate.
Based on these data, fill in the following table and explain your answers.
18 Activity 4.1/5.1
4.1/5.1 Test Your Understanding
Tube
number
Contents Explanation
1RNA Like DNA, RNA contains a sugar-phosphate backbone.
Activity 4.2/5.2 What predictions can you make about the
behavior of organic macromolecules if you know their structure?
1. Twenty amino acids are commonly utilized in the synthesis of proteins. These amino
acids differ in the chemical properties of their side chains (also called R groups).
What properties does each of the following R groups have? (Note: A side chain may
display more than one of these properties.)
Activity 4.2/5.2 19
R group Basic, acidic, or
neutral?
Polar or nonpolar? Hydrophilic or
hydrophobic?
c.
Basic Polar Hydrophilic
CH
2
CH
2
CH
2
CH
2
NH
3
+
2. Polypeptides and proteins are made up of linear sequences of amino acids. In its
functional form, each protein has a specific three-dimensional structure or shape.
Interactions among the individual amino acids and their side chains play a major role
in determining this shape.
a. How are amino acids linked together to form polypeptides or proteins? What is
this type of bond called?
20 Activity 4.2/5.2
b. Define the four structures of a protein. c. What kinds of bonds hold each of these
structures together?
Primary:
The linear sequence of amino acids in a
Covalent peptide bonds formed by
dehydration reactions hold the individual
3. Lipids as a group are defined as being hydrophobic, or insoluble in water. As a
result, this group includes a fairly wide range of compounds—for example, fats, oils,
waxes, and steroids like cholesterol.
a. How are fatty acids and glycerol linked together to form fats (triglycerides)?
Dehydration reactions between the OH of the carboxyl group on the fatty acid
b. What functions do fats serve in living organisms?
c. How do phospholipids differ from triglycerides?
Phospholipids have one of the OH groups of the glycerol interacting with a
d. What characteristics do phospholipids have that triglycerides do not have?
Phospholipids are amphipathic because the phosphate-containing side group is
4.2/5.2 Test Your Understanding
Use your understanding of the chemical characteristics of the four major
types of macromolecules in living organisms to predict the outcome of the following
experiments. Be sure to explain your reasoning.
Experiment 1: You stir 10 g of glucose and 10 mL of phospholipids in a 500-mL beaker
that contains 200 mL of distilled water. Draw a diagram to show where and how the
glucose and phospholipids would be distributed after you let the mixture settle for about
30 minutes.
The 10 g of glucose will dissolve in the water and be relatively evenly distributed in the
Experiment 2: You repeat Experiment 1, but this time you stir 10 g of glucose and 10 mL
of phospholipids in a different 500-mL beaker that contains 200 mL of distilled water and
100 mL of oil. Draw a diagram to show where and how the glucose, phospholipids, and
oil would be distributed after you let the solution settle for about 30 minutes.
As in Experiment 1, the 10 g of glucose will dissolve in the water and be relatively evenly
Experiment 3: To completely fill a sealed 500-mL glass container that contains 490 mL
of distilled water, you inject 10 mL of phospholipids into it. (A small gasket allows the
air to leave as you inject the phospholipids.) You shake this mixture vigorously and then
let it settle for an hour or more. Draw a diagram to show how the phospholipids would be
distributed in the container.
Experiment 4: A globular protein that is ordinarily found in aqueous solution has these
amino acids in its primary structure: glutamic acid, lysine, leucine, and tryptophan.
Predict where you would find each amino acid: in the interior portion of the protein
(away from water) or on the outside of the protein (facing water). (Refer to Figure 5.16,
page 79.)
Experiment 5: Drawn below is part of the tertiary structure of a protein showing the
positions of two amino acids (aspartic acid and lysine). Replacing lysine with another
amino acid in the protein may change the shape and function of the protein. Replacing
lysine with which type(s) of amino acid(s) would lead to the least amount of change in
the tertiary structure of this protein? (Refer to Figure 5.16, page 79.)
22 Activity 4.2/5.2