CHAPTER 10
The Structure and Function
of DNA
1. Hereditary information is stored in the chemical language of DNA.
2. DNA directs the biochemical, cellular, anatomical, and physiological activities of the
human body.
3. Scientists can manipulate the DNA of cells to modify the traits of crops, transform the
characteristics of cells, and treat and potentially prevent disease.
4. Viruses play a key role in the history of molecular biology and continue to be important
pathogens in humans, bacteria, plants, and animals.
5. Treatments and cures for viral infections are likely to be the products of research into
molecular biology.
Biology and Society: Tracking a Killer
1. Explain how flu vaccines are produced and why flu vaccines are important.
DNA: Structure and Replication
2. Explain what was and was not known about DNA by the early 1950s.
3. Describe and compare the chemical compositions of DNA and RNA.
4. Describe the key features of the overall shape of a DNA molecule. Explain how Watson
and Crick determined the structure of DNA.
5. Describe the process of DNA replication.
The Flow of Genetic Information from DNA to RNA to Protein
6. Define transcription and translation. Explain why the hypothesis “one gene-one
enzyme” is not correct.
7. Explain how the language of DNA directs the production of polypeptides.
8. Explain how codons are used to construct polypeptides. Explain what the authors mean
when they state “there is redundancy in the code but no ambiguity.”
9. Describe the steps of transcription and the processing of RNA before it leaves the
nucleus.
10. Compare the structures and functions of mRNA, tRNA, and rRNA.
11. Describe in detail the process of translation.
12. Distinguish between insertion, deletion, and substitution mutations. Explain how
mutations can be harmful or beneficial to organisms.
Viruses and Other Noncellular Infectious Agents
13. Compare the lytic and lysogenic cycles of bacteriophages.
14. Compare the life cycles of RNA and DNA viruses. Describe the spread, symptoms, and
prevention of viral diseases in plants and animals.
15. Describe the reproductive cycle of retroviruses such as HIV and the mechanisms by
which AZT and protease inhibitors limit AIDS.
16. Explain how viroids and prions cause disease.
Evolution Connection: Emerging Viruses
17. Describe the three processes that contribute to the emergence of viral disease.
Key Terms
adenine (A)
AIDS
bacteriophages
cap
codon
cytosine (C)
DNA
DNA polymerase
double helix
emerging viruses
exons
genetic code
guanine (G)
HIV
introns
lysogenic cycle
lytic cycle
messenger RNA
molecular biology
mutagen
mutation
nucleotide
phages
polynucleotide
prion
promoter
prophage
provirus
retrovirus
reverse transcriptase
ribosomal RNA (rRNA)
RNA polymerase
RNA splicing
start codon
stop codon
sugar-phosphate backbone
tail
terminator
thymine (T)
transcription
transfer RNA (tRNA)
translation
uracil (U)
virus
Word Roots
muta = change; gen = producing (mutagen: a physical or chemical agent that causes
mutations)
phage = eat (bacteriophages: viruses that attack bacteria)
poly = many (polynucleotide: a polymer of many nucleotides)
pro = before (prophage: phage DNA inserted into the bacterial chromosome before viral
replication)
retro = backward (retrovirus: an RNA virus that reproduces by first transcribing its RNA
into DNA then inserting the DNA molecule into a host’s DNA)
trans = across; script = write (transcription: the transfer of genetic information from DNA
into an RNA molecule)
Student Media
Activities
The Hershey-Chase Experiment
DNA and RNA Structure
DNA Double Helix
DNA Replication: An Overview
Overview of Protein Synthesis
Transcription
RNA Processing
Translation
Simplified Viral Reproductive Cycle
Phage Lytic Cycle
Phage Lysogenic and Lytic Cycles
Retrovirus (HIV) Reproductive Cycle
BioFlix
DNA Replication
Protein Synthesis
Biology Labs On-Line
TranslationLab
BLAST Animations
Hydrogen Bonds in DNA
Structure of DNA Double Helix
Transcription
Translation
Roles of RNA
HIV Structure
AIDS Treatment Strategies
MP3 Tutors
DNA to RNA to Protein
Process of Science
What Is the Correct Model for DNA Replication?
How Is a Metabolic Pathway Analyzed?
How Do You Diagnose a Genetic Disorder?
What Causes Infections in AIDS Patients?
Why Do AIDS Rates Differ Across the U.S.?
Videos
Discovery Channel Video: Vaccines
Discovery Channel Video: Emerging Diseases
Relevant Current Issues in Biology Articles
Current Issues in Biology, volume 2 (ISBN 0-8053-7108-7)
Detecting Mad Cow Disease
Tumor-Busting Viruses
Current Issues in Biology, volume 3 (ISBN 0-8053-7527-9)
Are Viruses Alive?
Current Issues in Biology, volume 4 (ISBN 0-8053-3566-8)
Preparing for a Pandemic
Founder Mutations
Current Issues in Biology, volume 5 (ISBN 0-321-54187-1)
Cancer Clues from Pet Dogs
Current Issues in Biology, volume 6 (ISBN 0-321-59849-0)
Diet Advice From DNA
Traces of a Distant Past
Relevant Songs to Play in Class
“The Jean Genie,” David Bowie
“Billy Jean,” Michael Jackson
“In Those Jeans,” Ginuwine
“Cat DNA,” Ozric Tentacles
Chapter Guide to Teaching Resources
DNA: Structure and Replication
Student Misconceptions and Concerns
1. If your class has not yet studied Chapter 3, consider assigning the Chapter 3 section on
“Nucleic Acids” before addressing the contents of Chapter 10.
2. The text describes but does not specifically point out that DNA replication is
semiconservative. Tell your students about an experiment in which a DNA molecule is
labeled, then replicated. How will the two DNA molecules compare with regard to the
location/distribution of the original DNA molecule? Will one DNA molecule be the
original and the other the new copy? Or is there another possibility? Half of each of the
two DNA molecules is new and half is the original, thus it used semiconservative
replication. Analogies for semiconservative replication can be a challenge. But in a
sense, DNA replication is similar to parents getting divorced and then each parent
remarrying someone else. The two new couples represent “half old parent and half new
person.”
3. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps just to
note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides, and
nucleotides include bases as part of their structure.
Teaching Tips
1. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are
like a train of various lengths and combinations of four types of train cars (monomers).
Proteins are also “trains” of various lengths but made of a combination of 20 types of train
cars.
2. The descriptions of the discovery of DNA’s structure are a good time to point out
that science is a collaborative effort. You might remind your class of all the prior
research (identifying DNA as the genetic material and clues to its structure) that brought
Watson and Crick to their historic conclusions.
3. The authors note that the structure of DNA is analogous to a twisted rope ladder. In
class, challenge your students to explain what the parts of the ladder represent. The
wooden rungs represent a base pair and each rope the sugar-phosphate backbone.
4. Demonstrate the complementary base pairing within DNA. Present students with
the base sequence to one side of a DNA molecule and have them work quickly at their
seats to determine the sequence of the complementary strand. For some students, these
sorts of quick practice are necessary to reinforce a concept and break up a lecture.
5. To explain the adaptive advantage of multiple replication sites over a single site of
replication, ask your students to imagine copying, by hand, the first ten chapters of your
biology textbook. The task would certainly go faster if ten students each copied a
different chapter!
6. There are about 2 million characters (letters or numbers) in the Campbell Essential
Biology with Physiology textbook. The accuracy of DNA replication would be like copying
every letter and number in this textbook by hand 500 times and writing just one letter or
number incorrectly, making one error in every 1 billion characters!
The Flow of Genetic Information from DNA to RNA to Protein
Student Misconceptions and Concerns
1. Less experienced students are often intensely focused on writing detailed notes. The risk
is that they miss the overall patterns and the broader significance of the topics discussed.
Consider a gradual approach to the subjects of transcription and translation, beginning quite
generally and testing comprehension, before venturing into the finer mechanics of each
process.
2. Consider placing on the board the basic content from Figure 10.9, noting the
sequence, products, and locations of transcription and translation in eukaryotic cells.
This reminder can create a quick concept check for students as they learn additional
detail.
3. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations
may be considered a part of a positive creative process. The dual nature of mutations,
potentially deadly yet potentially innovative, should be clarified.
Teaching Tips
1. It has been said that, “Everything about an organism is an interaction between the
genome and the environment.” You might wish to challenge your students to explain the
significance and validity of this statement.
2. The authors note that the sequential information in DNA and RNA is analogous to
the sequential information in the letters of a sentence. This analogy is also helpful when
explaining the impact of insertion or deletion mutations that cause a shift in the reading
frame.
3. The transcription of DNA into RNA is like a reporter who transcribes a political
speech. In both situations, the language remains the same, although in the case of the
reporter, it changes its form from spoken to written.
4. A parallel can be drawn between the discovery in 1799 of the Rosetta stone, which
provided the key that enabled scholars to crack the previously indecipherable
hieroglyphic code, and the cracking of the genetic code in 1961. Consider challenging
your students to explain what part of the genetic code is similar to the Rosetta stone.
This could be a short in-class activity for small groups.
5. Another advantage to the use of RNA to direct protein synthesis is that the original
code (DNA) remains safely within the nucleus, away from the many potentially
damaging chemicals in the cytoplasm. This is like making photocopies of important
documents for study, keeping the originals safely stored away.
6. The production of proteins is like a machine requiring fuel. The molecular
machinery (ribosomes and tRNA) used in many cellular processes also requires an input
of energy in the form of ATP.
7. If you were using a train analogy for the assembly of monomers into polymers, at
this point the DNA and RNA “trains” are traded in 3 for 1 for the polypeptide “train.”
Thus, in general, polypeptides have about 1/3 as many monomers as the mRNA that
coded for them.
8. After translation is addressed, consider asking your students (working singly or in
small groups) to list all of the places where base pairing is used (in the construction of a
DNA molecule during DNA replication, in transcription, and during translation when
the tRNA attaches).
9. Students might want to think of the A and P sites as stages in an assembly line. The
A site is where a new amino acid is brought in, according to the blueprint of the codon
on the mRNA. The P site is where the growing product/polypeptide is anchored as it is
being built. To help them better remember details of translation, students might think of
the letters for the two sites to mean “A” for addition, where an amino acid is added, and
“P” for polypeptide, where the growing polypeptide is located.
10. A simple way to demonstrate the effect of a reading frame shift is to have students
compare the following three sentences. The first is a simple sentence. But look what
happens when a letter is added (2) or deleted (3). The “reading frame,” or triplet
groupings, are re-formed into nonsense.
(1) The big red pig ate the red rag.
(2) The big res dpi gat eth ere dra g.
(3) The big rep iga tet her edr ag.
11. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It
is not likely to improve a genome any more than shooting a bullet through the hood of a car
is likely to improve engine performance!”
Viruses and Other Noncellular Infectious Agents
Student Misconceptions and Concerns
1. Students and many parents with young children expect a treatment of antibiotics for
many respiratory infections, even though such infections may result from a virus. Students
will benefit by a thorough explanation of the inappropriate use of antibiotics for viral
infections and the risks of overuse of antibiotics leading to increased numbers of antibioticresistant bacteria.
2. The success of modern medicine has perhaps led to an overconfidence in our ability to
treat disease. Students often do not understand that there are few successful treatments for
viral infections. Instead, the best defense against viruses is prevention by reducing the
chances of contacting the virus and the use of vaccines.
Teaching Tips
1. Students (and instructors) might enjoy thinking of a prophage as a smudge mark on the
master copy of a class handout. The smudge is replicated every time the original is copied!
2. Viruses can spread throughout a plant by moving through plasmodesmata (not
specifically discussed in this chapter). This is like smoke spreading throughout a
building by moving through air ducts.
3. There is an interesting relationship between the speed at which a virus kills or
debilitates a host and the extent to which it spreads from one organism to another. This
is something to consider for a class discussion. Compare two viral infections. Infection
A multiplies within the host, is spread by the host to other people through casual
contact, but does not cause its lethal symptoms until 5–10 years after infection. Virus B
kills the host within 1–2 days of infection, is easily transmitted, and causes severe
symptoms within hours of contact. Which virus is likely to spread the fastest through
the human population on Earth? Which might be considered the most dangerous to
humans?
4. Students often do not understand the disproportionate distribution of HIV infections and
AIDS in our world. Consider an Internet assignment, asking students to identify the regions
of the world most affected by HIV-AIDS. The Centers for Disease Control and Prevention
has extensive information about AIDS at www.cdc.gov/hiv/.
Answers to End-of-Chapter Questions
The Process of Science
12. Suggested answer: In this case, two of the daughter cells will have a double helix in
which both strands are radioactive. The other two daughter cells will have a double helix in
which one strand is radioactive and the other is nonradioactive.
13. Suggested answer: In this experiment one would expect to find the proteins (tagged with
radioactive sulfur) outside of the bacterial cells, whereas the viral DNA (tagged with
radioactive phosphorous) would be found inside the bacterial cells. This experiment
indicates that the viral DNA is the infectious particle as it was the only thing to enter the
bacterial cells.
Biology and Society
14. Some issues and questions to consider: Is it fair to issue a patent for a gene or gene
product that occurs naturally in every human being? Or, should a patent be issued only for
something new that is invented rather than found? Suppose another scientist slightly
modifies the gene or protein. How different does the gene or protein have to be so that the
patent is not infringed? Might patents encourage secrecy and interfere with the free flow of
scientific information? What are the benefits to the holder of a patent? When research
discoveries cannot be patented, what are the scientists’ incentives for doing the research?
What are the incentives for the institution or company that is providing financial support?
15. Tanning by exposure to ultraviolet light causes mutations in skin cells exposed to the
light. These mutations increase the risks of developing skin cancer.
Additional Critical Thinking Questions
The Process of Science
1. What would be the effect of the following mutations on the production of the protein for
which a gene codes?
a. a mutation in the promoter of a gene, so that RNA polymerase cannot bind to it
b. a mutation in an intron of a gene
c. a mutation of codon CGA to codon AGA in an exon
d. a mutation of a stop codon to one coding for an amino acid
Suggested answers:
a. A mutation in the promoter, preventing RNA polymerase binding, would mean that
the gene is never transcribed, and the protein is never made.
b. Since an intron is cut out of mRNA before it is translated, a mutation in an intron of
a gene would have no effect on the protein or its production.
c. Both of these codons correspond to the amino acid arginine, so there would be no
effect on the protein or its production.
d. The translation of the protein would not terminate properly but would continue until
a stop codon is reached. This would likely produce a protein with an altered
function or no function.
2. The base sequence of the gene coding for a short polypeptide is T A C G C T A G
G C G A T T G A C T. What would be the base sequence of the mRNA transcribed
from this gene? Using the genetic code in Figure 10.10, state the amino acid sequence
of the polypeptide translated from this mRNA.
Suggested answer: mRNA: AUGCGAUCCGCUAACUGA. Amino acids: Met-ArgSer-Ala-Asn.
3. In the early 1950s, scientists considered several different hypotheses about how
DNA is replicated. One hypothesis, called conservative replication, was that the doublestranded parental DNA molecule is conserved intact but somehow directs the synthesis
of a daughter DNA molecule consisting of two entirely new strands. Another
hypothesis, semiconservative replication, was that the two strands of the parental DNA
separate and each acts as a template for the construction of a new strand, yielding two
daughter molecules, that each have one old and one new strand. This hypothesis turned
out to be correct. Assume you grow bacteria in a medium containing radioactive
phosphorus, so all their DNA is labeled, and then you transfer them to a medium
containing only nonradioactive phosphorus. After precisely one cell division in the
nonradioactive medium, you test the bacterial DNA for radioactivity.
a. The results that would support the conservative replication hypothesis would be
that:
b. The results that would support the semiconservative replication hypothesis would
be that:
(For the two questions above, select one of the answers below, state why you chose it,
and state why you rejected each of the other choices.)
a. none of the DNA would be radioactive; all the DNA would be radioactive
b. all the DNA would be radioactive; half the DNA would be radioactive
c. half the DNA would be radioactive; all the DNA would be radioactive
d. None of these. This experiment would not be able to distinguish between the two
hypotheses.
Suggested answers:
a. No. The conservative replication theory would predict that after one cell division,
the DNA of half the cells would be entirely radioactive, and the DNA of the other
half of the cells would be all new and completely nonradioactive.
b. No. This is the reverse of the correct answer; see answer c.
c. Correct. The conservative replication hypothesis predicts that after one cell division,
half the cells will contain entirely new, nonradioactive DNA, and half the cells will
contain entirely old, radioactive DNA. The semiconservative replication hypothesis
predicts that each cell will have DNA consisting of one old strand (radioactive) and
one new strand (nonradioactive) and therefore that all the DNA molecules in all the
cells will contain some radioactivity.
d. No. This experiment could distinguish very well between the hypotheses.
Biology and Society
4. Our civilization generates many potentially mutagenic chemicals (pesticides, for
example) and modifies the environment in ways that increase exposure to other mutagens,
notably ultraviolet (UV) radiation. What role should government play in identifying
mutagens and regulating their release to the environment?
Some issues and questions to consider: Does the government have an obligation to protect
the health of its citizens? Can too much government regulation stifle the economy? What is
the proper balance between protection from harm and government regulation? Is it possible
to identify and monitor every possible mutagen? Should we try?
5. There are many environmental mutagens whose effects have been clearly noted in
humans. Some examples include the chemicals in cigarette smoke and UV exposure.
Knowing that the risks of exposure carry such high odds of a dangerous outcome such as
cancer, many people still voluntarily expose themselves to these mutagens. Should people
be responsible for regulating their own activities, or should there be more legislation to
prevent this? If people choose to smoke and then develop lung cancer or choose to
overexpose themselves to the sun and develop malignant melanoma, should they be held
accountable for their actions? If so, should they foot the bill for health care? Should their
insurance cover the expense? Should these people be able to sue others for financial gain
when they were fully aware of the dangers associated with the exposure?
Some issues and questions to consider: How responsible is a person for his or her own
actions? If the dangers are clearly indicated and the person makes their own choice, should
they suffer the consequences? Should insurance companies be responsible for paying for
claims that were derived in this manner? Should they be allowed to deny coverage for these
people? If so, where do they draw the line? Are you willing to pay higher insurance
premiums to cover these costs? Should the government do more to deter people from habits
such as smoking?