17 Bacteria and Viruses
ENCOUNTER THE PHENOMENON
Write the Encounter the Phenomenon question for this module.
What is alive in this photo?
Use the “What I Know” column to list the things you know about the Encounter the Phenomenon
question. Then list the questions you have about the Encounter the Phenomenon question in the
“What I Want to Find Out” column. As you read the module, fill in the “What I Learned” column.
W
What I Want to Find Out
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K
What I Know
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L
What I Learned
Bacteria and Viruses
1 Bacteria
REVIEW
VOCABULARY
prokaryotic cell
Recall the definition of the Review Vocabulary term.
prokaryotic cell
cell that does not contain any membrane-bound
organelles
NEW VOCABULARY
Use your book to define each term.
bacteria
bacteria
prokaryote that has peptidoglycan in its cell wall
nucleoid
circular area of a prokaryotic cell that holds the chromosome
capsule
layer of secreted polysaccharides around a prokaryotic cell wall
nucleoid
capsule
pilus
binary fission
pilus
conjugation
the outer surface of some prokaryotes; used in attachment
endospore
binary fission
submicroscopic, hairlike structure made of protein that is found on
conjugation
division of a cell into two genetically identical cells
method of reproduction in which two prokaryotes attach
to each other and exchange genetic information
endospore
structure produced by some bacteria during harsh
environmental conditions that contains genetic information and can
germinate into a new bacterial cell when conditions improve
1.
hot, acidic: sulfur hot springs, thermal vents, volcanoes
2.
high concentrations of salt: Great Salt Lake, Dead Sea
3.
oxygen-free: swamps, bogs, volcanic vents
Model a prokaryotic cell and label its structures.
Drawings should include all labels shown in Figure 3. Accept all
reasonable variations.
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Summarize three general environments where archaea live, and give
one example of each environment.
1 Bacteria (continued)
Get It?
flagella.
Explain the difference between prokaryotic and eukaryotic
Prokaryotic flagella are made of filaments, unlike the flagella of
eukaryotes, which are made of microtubules.
Identify each prokaryote shape below with its scientific name.
Cocci
Bacilli
Spirilla
Compare prokaryote reproduction by completing the table below.
Reproduction
Method
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Process
Binary Fission
Conjugation
chromosome replicates,
two individuals use
cell elongates, new
pili to attach to each
piece of plasma
other and exchange
membrane and cell wall
genetic material
forms and separates cell
Result
two genetically
new gene combination
identical cells
Compare prokaryotes by describing how each group below obtains
energy for cellular respiration.
Saprotrophs: decompose dead organisms or organic waste
Photoautotrophs: use light for photosynthesis
Chemoautotrophs: break down inorganic compounds that contain
nitrogen or sulfur; process is called chemosynthesis
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1 Bacteria (continued)
Get It? Summarize the importance of photosynthesis and cellular
metabolism in bacterial metabolism.
Photosynthesis and cellular metabolism are the basis for bacterial
metabolism. However, some bacteria are also chemoautotrophic. They
synthesize organic molecules without photosynthesis.
Identify two bacterial survival mechanisms and describe the
advantages of each mechanism.
Mechanism
Endospores
Survival Advantages
can survive extreme conditions that kill the
bacteria; germinate when conditions improve
produce new gene forms and combinations;
Mutations
increase chances that some can survive
environmental changes and repopulate
Get It?
Explain how mutations can help a population of bacteria
develop new adaptations in response to a change in the environment.
Mutations lead to new forms of genes, new gene combinations, new
characteristics, new adaptations, and genetic diversity. When the
distribution of traits in the population of bacteria changes, the bacteria
List five ways that bacteria are helpful to humans.
decompose dead organisms and recycle nutrients
Bacteria
are
helpful
nitrogen fixation
normal flora protect against disease and produce
vitamin K
used in producing foods and vitamin pills
used in producing antibiotics
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have adapted to the new environment.
1 Bacteria (continued)
CHECK YOUR PROGRESS
1. Diagram a bacterium.
Diagrams should include representations of the cell
wall, chromosome, pili, and capsule.
2. Discuss possible rationales that taxonomists might have used when deciding to
group prokaryotes into two distinct domains instead of in one group.
The two groups have different biochemical and genetic components and they live in different
environments.
3. Explain survival mechanisms of bacteria at both the individual and population levels.
Individually, bacteria form endospores that are resistant to harsh environments. Random genetic
mutations allow bacteria as a population to adapt to new conditions.
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4. List three ways bacteria are beneficial to humans.
Bacteria recycle nutrients in an ecosystem. E. coli produces vitamin K. Some bacteria are used to
make antibiotics or other medicines.
5. Analyze why it is more difficult for biologists to understand the diversity in
prokaryotes as compared to plants or animals.
The diversity in prokaryotes exists on the cellular level and is not visible to the naked eye.
6. Imagine that today at 1 P.M., a single Salmonella bacterial cell landed on potato
salad sitting on your kitchen counter. Assuming optimal conditions for bacterial
growth, how many bacterial cells will be present at 3 P.M. today?
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Bacteria and Viruses
2 Viruses and Prions
REVIEW
VOCABULARY
protein
NEW VOCABULARY
virus
capsid
lytic cycle
lysogenic cycle
retrovirus
prion
Recall the definition of the Review Vocabulary term.
protein
large, complex polymer composed of carbon, hydrogen,
oxygen, nitrogen, and sometimes sulfur
Use the new vocabulary terms in the left column to complete the
following paragraph.
virus
A
is genetic material within a protein coat, but
it has no organelles or other characteristics of life. The genetic
capsid
material lies inside its
, or outer layer of protein. In
the
lytic cycle
viral genes instruct the host cell to make
many copies of the viral RNA or DNA. Some viruses replicate in a
lysogenic cycle , in which the viral DNA integrates into a host
chromosome and lies dormant for some time. A
retrovirus
,
such as the HIV virus, contains RNA instead of DNA. Mutation in
the genes of a normal protein called a
prion
is responsible
for diseases such as “mad cow.”
ACADEMIC
VOCABULARY
widespread
Define widespread to show its scientific meaning.
widely diffused or prevalent
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238
2 Viruses and Prions (continued)
Sketch t he general structure of a virus.
Sketches should show nucleic acids, DNA, or RNA in
its core, and an outer protein coat.
Synthesize why many viruses cannot pass from one species to
another.
The virus attaches to the host cell using specific receptors on the
plasma membrane of the host. Different types of organisms have
receptors for different types of viruses, limiting transmission
between species.
Label steps A, B, C, D, and E of a lytic cycle in the figure below. Use
the following terms.
• Assembly
•Attachment
• Lysis and Release
• Replication
Bacteriophage
Nucleic
acid
• Entry
Bacterial DNA
Bacterial
host cell
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A
Attachment
B
Entry
The bacteriophage
injects its nucleic acid
into the bacterial cell.
E
Lysis and Release
The host cell breaks open and
releases new virus particles.
C
D
Assembly
New virus
particles are
assembled.
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C18-05C-873043-BO-A
Replication
The host’s
metabolic
machinery makes
viral nucleic acid
and proteins.
2 Viruses and Prions (continued)
Sequence the steps of a lysogenic cycle.
Viral DNA integrates into a chromosome of a host cell.
There the viral genes remain dormant for months or years.
Activation triggers the lytic cycle to begin.
New viruses leave the cell by exocytosis or by bursting the cell.
Evaluate and discuss the role of reverse transcriptase in the
replication cycle of HIV.
After HIV attaches to a cell and releases its RNA, the reverse
transcriptase enzyme synthesizes DNA using the viral RNA as
a template.
Summarize information about prions by completing the table.
What causes a prion to become
harmful?
It mutates.
How might humans contract a
prion-caused disease?
by eating beef from an infected
cow
What is the result of prion
infection?
Prions infect nerve cells in the
brain, causing them to burst.
SUMMARIZE
Conclude whether viruses that replicate by the lytic cycle or the lysogenic cycle are more
dangerous. Explain your reasoning. Accept all reasonable responses.
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What is a prion?
a protein that normally exists in
cells but can cause infection or
disease
2 Viruses and Prions (continued)
CHECK YOUR PROGRESS
1. Describe how viruses and prions can alter cell functions.
Viruses cause an infected cell to make more viruses; prions cause proteins inside cells to mutate and
change shape and function incorrectly.
2. Compare and contrast similarities and differences in the replication of a herpes
simplex virus with a human immunodeficiency virus.
Herpes viruses have DNA; HIV has RNA. HIV contains reverse transcriptase. Replication is similar in
that genetic material from both enters the host cell nucleus.
3. Draw a diagram of a virus and label the parts.
Students should provide a diagram similar to Figure 11.
4. Sequence the steps in the process of how prions might be transmitted from cattle
to humans.
Possible answer: (1) The cattle-butchering process releases prions into the meat. (2) Humans
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consume the infected meat. (3) Prions travel to the brain.
5. Propose ideas for the development of drugs that could stop viral replication cycles.
prevent a virus from attaching to host cells; disrupt the viral replication process; prevent the final
assembly of new viral particles
6. Write a paragraph explaining why it is difficult to make drugs or vaccines that
effectively fight against HIV, given the fact that each time reverse transcriptase
works, it makes a slight miscopy.
Paragraphs should indicate that each time HIV replicates, a slightly different type of the virus
forms, so drugs or vaccines might be ineffective.
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