CHAPTER 3
The Molecules of Life
Why This Chapter Matters
1. Biological molecules are the building blocks of cells, the fundamental units of life.
2. Knowing the structures, properties, and roles of the four major classes of organic
molecules (carbohydrates, lipids, proteins, and nucleic acids) is essential to
understanding the characteristics of life.
3. Carbohydrates, proteins, and lipids are vital components of our diets and the diets of
most organisms.
4. Regional differences in lactose intolerance illustrate a medically significant aspect of
human evolution.
Chapter Objectives
Biology and Society: Got Lactose?
1. Describe the causes and consequences of lactose intolerance.
Organic Compounds
2. Describe the special bonding properties of carbon that allow it to form an endless
variety of organic molecules.
3. Compare a dehydration reaction to hydrolysis.
Large Biological Molecules
4. Compare the structures and roles of monosaccharides, disaccharides, and
polysaccharides in living organisms. Give examples of each.
5. Compare the structure and properties of saturated and unsaturated fatty acids.
6. Distinguish between steroids and anabolic steroids, and explain how the use of anabolic
steroids can be dangerous to a person’s health.
7. Describe the structure of proteins. Distinguish between the primary structure and the
final three-dimensional shape.
8. Describe and compare the structures of DNA and RNA.
Evolution Connection: Evolution and Lactose Intolerance in Humans
9. Explain why lactose intolerance has evolved differently in humans spread throughout
the world.
Key Terms
amino acid
atherosclerosis
carbohydrates
cellulose
dehydration reaction
denaturation
disaccharides
DNA
double helix
fat
functional groups
gene
glycogen
hydrocarbons
hydrogenation
hydrolysis
hydrophilic
hydrophobic
isomers
lipids
macromolecules
monomers
monosaccharides
nucleic acids
nucleotides
organic compounds
peptide bond
polymers
polypeptide
polysaccharides
primary structure
protein
RNA
saturated
starch
steroids
sugar-phosphate backbone
trans fat
triglyceride
unsaturated
Word Roots
di = two; sacchar = sugar (disaccharide: two monosaccharides joined together)
glyco = sweet; gen = producing (glycogen: a polysaccharide sugar used to store energy)
hydro = water; lyse = break (hydrolysis: breaking chemical bonds by adding water)
iso = equal; meros = part (isomer: molecules with similar molecular formulas but different
structures)
macro = big (macromolecules: a giant molecule in living organisms)
mono = single (monosaccharide: simplest type of sugar)
philic = loving (hydrophilic: water-loving property of a molecule)
phobos = fearing (hydrophobic: water-repelling property of a molecule)
poly = many (polymer: a chain made from smaller organic molecules)
sclero = hard (atherosclerosis: hardening of the arteries)
tri = three (triglyceride: a glycerol molecule joined with three fatty acid molecules)
Student Media
Activities
Diversity of Carbon-Based Molecules
Functional Groups
Making and Breaking Polymers
Models of Glucose
Carbohydrates
Lipids
Protein Functions
Protein Structure
Nucleic Acid Functions
Nucleic Acid Structure
Biology Labs On-Line
HemoglobinLab
BLAST Animations
Alpha Helix
Protein Primary Structure
Protein Secondary Structure
Protein Tertiary and Quaternary Structure
MP3 Tutors
Protein Structure and Function
DNA Structure
Process of Science
What Factors Determine the Effectiveness of Drugs?
You Decide
Low-Fat or Low-Carb Diets—Which I Healthier?
Relevant Current Issues in Biology Articles
Current Issues in Biology, volume 1 (ISBN 0-8053-7507-4)
Rebuilding the Food Pyramid
Current Issues in Biology, volume 2 (ISBN 0-8053-7108-7)
Detecting Mad Cow Disease
Current Issues in Biology, volume 5 (ISBN 0-321-54187-1)
Eating Made Simple
Current Issues in Biology, volume 6 (ISBN 0-321-59849-0)
Diet Advice From DNA
Relevant Songs to Play in Class
“Sugar, Sugar,” The Archies
“I’ve Got You Under My Skin,” Frank Sinatra
Chapter Guide to Teaching Resources
Organic Compounds
Student Misconceptions and Concerns
1. General biology students might not have previously taken a chemistry course. The
concept of molecular building blocks that cannot be seen can be abstract and difficult to
comprehend for such students. Concrete examples from our diets and good images will
increase comprehension.
2. Students might need to be reminded about the levels of biological organization. The
relationship between atoms, monomers, and polymers can be confusing as each is discussed.
Consider noting these relationships somewhere in the classroom (such as on the board)
where students can quickly glance for reassurance.
Teaching Tips
1. A drill with interchangeable drill bits is a nice analogy to carbon skeletons with
different functional groups. The analogy supports the role of different functions with
different structures.
2. Train cars linking together to form a train is a nice analogy to monomers linking to form
polymers. Consider adding that as the train cars are joined, a puff of steam appears—thus,
the reference to water production and a dehydration reaction when linking molecular
monomers.
Large Biological Molecules
Student Misconceptions and Concerns
1. The abstract nature of chemistry can be discouraging to many students. Consider
starting out this section of the lecture by examining the chemical groups on a food nutrition
label. Candy bars with peanuts are particularly useful as they contain significant amounts of
all three sources of calories (carbohydrates, proteins, and lipids).
2. Consider reinforcing the three main sources of calories with food items that clearly
represent each group. Bring clear examples to class as visual references; for example, a can
of Coke or a bag of sugar for carbohydrates, a tub of margarine for lipids, and some beef
jerky for protein (although some fat and carbohydrates might also be included).
Teaching Tips
1. If your lectures will eventually include details of glycolysis and aerobic respiration, this
is a good point to introduce the basic concepts of glucose as fuel. Just introducing this
conceptual formula might help: eating glucose + breathing in oxygen (yields) water + usable
energy (used to build ATP) + heat + exhaled CO2.
2. The section about our use of sugars may be of considerable interest to your students,
who might not be expecting much interest in a lecture about organic chemistry. Consider an
assignment for each student to bring to class a product label indicating high-fructose corn
syrup (HFCS) as an ingredient.
3. Learning the definitions of word roots is invaluable when learning science. Learning the
meaning of the prefix word roots “mono” (one), “di” (two), and “poly” (many) helps to
distinguish the structures of various carbohydrates.
4. Consider an assignment for students to access the Internet and find reliable sources that
discuss high sugar consumption in the modern diet. The key, of course, is in the quality of
the resource. Consider narrowing down the categories to certain nonprofit health
organizations (American Cancer Society, American Heart Association, and the like) and
peer-reviewed journals.
5. A simple demonstration can illustrate hydrophobic and hydrophilic substances. In front
of the class, mix colored water and a yellow oil (corn or canola oil work well). Shake up the
mixture and then watch as the two separate. (You may have a mixture already made that
remains separated; however, the dyes may bleed between the oil and the water.)
6. Margarine in stores commonly comes in liquid squeeze containers, in tubs, and in sticks.
These forms reflect increasing amounts of hydrogenation, gradually increasing the stiffness
from a liquid, to a firmer spread, to a firm stick of margarine. As noted in the text, recent
studies have suggested that unsaturated oils become increasingly unhealthy as they are
hydrogenated. Perhaps your students can find references to this correlation on the Internet.
7. Many analogies relate to students the diversity of proteins that can be made from just 20
amino acids. The authors note that our language uses combinations of 26 letters to form
words. Proteins are much longer “words,” creating even more diversity. Another analogy is
to trains. This builds on the earlier analogy when polymers were introduced. Imagine
making different trains about 100 cars long, using any combination of 20 types of railroad
cars. Mathematically, the number of possible trains is 20100, a number beyond imagination.
8. The functional significance of protein shape is an abstract molecular example of form
and function relationships, which might be new to some students. The binding of an enzyme
to its substrate is a type of “molecular handshake,” which permits specific interactions. To
help students think about form and function relationships, share some concrete analogies in
their lives—perhaps flathead and Phillips screwdrivers that match the proper type of screws
or the fit of a hand into a glove.
9. The authors note that the difference between a polypeptide and a protein is analogous to
the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are
clearly more complex!
10. Most cooking results in changes in the texture and color of a food. The brown color of a
steak is the product of the denaturation of proteins. Fixatives such as formalin also denature
proteins and cause color changes. Students who have dissected vertebrates will realize that
the brown color of the muscles makes it look as if the animal has been cooked.
11. Consider this assignment to wrap up the presence of organic molecules in our diets.
Have students working individually or in small groups analyze a food label listing the
components of a McDonald’s Big Mac. Note the most abundant organic molecule class
(perhaps by weight) found in each component.
12. The “NA” in DNA and RNA represents “nucleic acid.” Students often do not make this
association without assistance.
Answers to End-of-Chapter Questions
The Process of Science
12. Suggested answer: A long hydrocarbon chain ending in a carboxyl group is a fatty acid.
Fatty acids and glycerol are the molecules that result when fats (triglycerides) are
hydrolyzed. The evidence thus suggests that the cake mix does contain fat. To further
support this hypothesis, intact fat molecules must be isolated from the mix.
13. Suggested answer: Each mutant version of the lactase enzyme would need to be tested
on lactose. The enzyme could be added to lactose and the products could be analyzed. If
glucose and galactose were present, then the enzyme did in fact work; therefore, its shape
has not been significantly altered. If glucose and galactose were not present after the
enzyme had been added to lactose, then the shape of the enzyme has been significantly
altered so that it can no longer do its job.
Biology and Society
14. Some additional issues and questions to consider: Is it fair for some athletes to have an
“edge” over their competitors who are not using anabolic steroids? Is the competition so
fierce that athletes are willing to assume the health risks for the athletic advantage? Should
various private agencies and/or the government regulate the use of steroids? Should athletes
randomly be tested for steroid use? Should athletes be disqualified from events if they have
used anabolic steroids? Should all professional sports be subject to testing with similar
penalties?
15. Some additional issues and questions to consider: Should individuals be responsible for
the consequences of their own actions? What, if any, distinctions can you make between
people choosing to smoke versus people who consume fast food? Should courts be involved
in such decisions? What can fast-food companies do to make the “dangers” of their products
obvious to the consumers? Should insurance costs be raised to provide the money needed to
care for the health of individuals who choose to smoke or eat unhealthy foods?
16. Some additional issues and questions to consider: How are these chemicals important in
agriculture, medicine, and public health? How have they affected humans? Wildlife?
Natural vegetation? Are the chemicals themselves harmful, or is the way that they are used
harmful? What influences have shaped your opinions? The media? Personal experience?
Reading? Friends and family? How might the opinion of a villager in a developing country
differ from yours?
Additional Critical Thinking Questions
The Process of Science
1. We always hear that starchy foods are a great source of nutrition because the glucose
molecules that are contained within the starch can be used for energy. People often tell you
to eat starchy foods prior to an athletic event. Cellulose (or fiber) is also made of many
glucose molecules. Why don’t people tell you to eat lots of cellulose prior to an athletic
event? Make sure your answer explains the chemical difference between starch and
cellulose.
Suggested answer: Although starch and cellulose are both made of glucose molecules,
the difference between them is how those glucose molecules are bonded together. We
have the enzymes to break the bonds in starch to release glucose, which can be used for
energy. We are lacking enzymes to break the bonds in cellulose. This means that the
glucose contained within cellulose can’t be used.
2. Linus Pauling believed that large doses of vitamin C can help prevent the common cold,
cancer, and other diseases. Imagine you have been given a research grant by the National
Institutes of Health to evaluate Pauling’s claims. How would you go about setting up an
experimental study to determine whether vitamin C can prevent colds? How would you
evaluate the results of your study?
Some issues and questions to consider: How will you choose your test subjects? How
many subjects should you have? Will you give them all vitamin C or just some of them?
What criteria will you use to divide the test subjects into groups? What is a control
group? Should the subjects know whether they are getting vitamin C or not? Should the
experimenters who are giving out the drug and measuring the severity of cold symptoms
know which of the subjects are getting vitamin C? What is a double-blind study? If
there is a difference between your groups, how can you be sure it is due to vitamin C?
3. Answer the following based on the information provided on these nutritional labels.
Product A
Product B
Total fat
30 g
26 g
Saturated fat
8g
10 g
Monounsaturated fat
10 g
10 g
Polyunsaturated fat
12 g
6g
Which product would you select if you were concerned about your health? Give two
reasons why you would select that product. If the ingredient label of this product
mentioned the term hydrogenated oils, what would that term mean? Manufacturers have
gotten away with some fairly questionable labeling procedures to deceive consumers
concerning the actual nutritional content of their products. Do you think that the U.S.
Food and Drug Administration (FDA) should make some changes to the nutritional
labels?
Suggested answer: Product A is the better choice. It has less saturated fat and more
polyunsaturated fat. If hydrogenated oils were present, this would indicate that
unsaturated fats have had hydrogens added, which essentially makes them the same as a
saturated fat. These hydrogenated fats are typically referred to as trans fats to deceive
the consumer.
Biology and Society
4. Scientists are working on a radically new type of computer designed to use DNA as the
information material rather than the silicon chips found in today’s computers. What is the
basis for using DNA as an information storage and processing molecule? What are some of
the potential advantages and disadvantages of this technology?
Some issues and questions to consider: Electronic computers with silicon chips store
information in one of only two forms: on or off. DNA, however, has four different bases
(A, T, C, and G). In addition, DNA is a very small molecule compared to a silicon chip;
therefore, DNA might be able to dramatically reduce the size and increase the speed and
storage capacity of computers. Most electronic computers work linearly—that is, they
process data sets one after the other (much like your reading of this sentence). A DNA
computer, however, is based on biochemical reactions using DNA as the reactant. These
reactions can occur in parallel: Billions of DNA molecules can undergo a biochemical
reaction (like copying the DNA) simultaneously. However, chemical reactions can be
slow and may not occur faithfully. DNA is capable of mutation, so why not DNA
computers? Can we (as thinking human beings) be considered DNA computers? Would
a DNA computer of the future be considered a living thing?
5. The term organic is perceived by most people to mean that such products are natural
and harmless. Each year, industrial chemists develop and test thousands of new organic
compounds for use as pesticides, fungicides, and weed killers. In what ways are these
chemicals useful and important to us? In what ways can they be harmful? Is your general
opinion of pesticides positive or negative?
Some issues and questions to consider: How are these chemicals important in
agriculture, medicine, and public health? How have they affected humans? Wildlife?
Natural vegetation? Are the chemicals themselves harmful, or is the way that they are used
harmful? What influences have shaped your opinions? The media? Personal experience?
Reading? Friends and family?