AP Biology 12
Concept 1 continued: Analyzing components
and reproduction cycles of viruses
Please refer to:
Chapter 19 in Campbell
pg 134-136 in
Holtzclaw
Practice Questions:
Holtzclaw: #2,10
p.143,144
Campbell: #1,2 (19.1)
p. 384
#1, 2, 3, 4 (19.2) p. 390
#1,2,3,8 p. 395
,
Learning Intentions
You must know:
The components of a virus
The differences between lytic and lysogenic
cycles
Can you find the viruses?
What are the viruses infecting?
What does this
bacteriophage virus
remind you of?
How were viruses first discovered?
Waaaaay smaller
than bacteria!
Tobacco mosaic
disease
How does this
experiment
support the idea
of viruses?
Discuss: Are viruses alive or dead?
Why? What defines a virus? What
defines life?
Try This!
 Which of the following is not a property of
life shared by prokaryotic cells,
eukaryotic cells, and viruses?
A. nucleic acids used to store hereditary
information
B. order and complexity in arrangement of
biological molecules
C. the ability to process energy through
metabolic reactions
D. the capacity to evolve
Try This!
 Which of the following is not a property of
life shared by prokaryotic cells,
eukaryotic cells, and viruses?
A. nucleic acids used to store hereditary
information
B. order and complexity in arrangement of
biological molecules
C. the ability to process energy through
metabolic reactions
D. the capacity to evolve
Try This! Viruses:“a kind of borrowed life”
 Classify each statement as TRUE or FALSE,
and identify which statement supports the view
of most biologists that viruses are nonliving.
A. Viruses are two-dimensional, rather than threedimensional.
B. The viral genome may be single- or double-stranded.
C. Viruses are obligate intracellular parasites.
D. An isolated virus is unable to replicate its genes or
regenerate ATP.
Try This! Viruses:“a kind of borrowed life”
 Classify each statement as TRUE or FALSE,
and identify which statement supports the view
of most biologists that viruses are nonliving.
A. Viruses are two-dimensional, rather than threedimensional. FALSE
B. The viral genome may be single- or double-stranded.
TRUE
C. Viruses are obligate intracellular parasites. TRUE
D. An isolated virus is unable to replicate its genes or
regenerate ATP. TRUE
What is a virus made of?
 Genetic material: single
or double stranded DNA
or single or double
stranded RNA
 Protein shell: capsid
 Some viruses also have
viral envelopes from
membrane of host cells
Compare the structure of these two
viruses:
Compare the structure of these three viruses:
Try This!
 Bacteriophages were grown in a medium
containing radioactive sulfur (35S) and
radioactive phosphorous (32P), which are
incorporated into proteins and DNA,
respectively. If these phages were used to
infect a bacterial culture, which isotope would
be detected within the infected bacteria?
A. 35S
B. 32P
C. both
D. neither
Try This!
 Bacteriophages were grown in a medium
containing radioactive sulfur (35S) and
radioactive phosphorous (32P), which are
incorporated into proteins and DNA,
respectively. If these phages were used to
infect a bacterial culture, which isotope would
be detected within the infected bacteria?
A. 35S
B. 32P
C. both
D. neither
How do viruses replicate?
Overall: Simplified
Viral Reproduction
(Campbell Online)
How do viruses replicate?
Bacteriophage: Lytic vs lysogenic cycles
(Campbell)
(Campbell)
How does a virus replicate?
Retroviruses (Campbell))
Use the enzyme
reverse
transcriptase
Example: HIV
Try This!
 AZT is a nucleoside analog used to treat HIV
infections. It is a thymine (T) nucleoside with
an azide group instead of the hydroxyl group
found in typical thymine nucleosides. Which
step does AZT hamper in the reproductive
cycle of the HIV virus?
A.
B.
C.
D.
entry into the cell
reverse transcription of DNA from RNA
transcription of RNA from proviral DNA
viral assembly within the cell
Try This!
 AZT is a nucleoside analog used to treat HIV
infections. It is a thymine (T) nucleoside with
an azide group instead of the hydroxyl group
found in typical thymine nucleosides. Which
step does AZT hamper in the reproductive
cycle of the HIV virus?
A.
B.
C.
D.
entry into the cell
reverse transcription of DNA from RNA
transcription of RNA from proviral DNA
viral assembly within the cell
Viroids and Prions: the really little guys
Viroids – circular RNA
Mostly affects plants
Prions – misfolded, infectious protein
Example: Mad Cow
Try This!
 Identify all correct statements.
A. Unlike viruses, viroids do not encode proteins.
B. Unlike viruses, the genetic material of a viroid
is RNA.
C. Unlike viruses, prions are infectious proteins.
D. Unlike viruses, prions do not include any
nucleic acids.
Try This!
 Identify all correct statements.
A. Unlike viruses, viroids do not encode proteins.
B. Unlike viruses, the genetic material of a viroid
is RNA.
C. Unlike viruses, prions are infectious proteins.
D. Unlike viruses, prions do not include any
nucleic acids.
Beautiful viral animation
Hepatitis C virus
Viral structures
Discovery Channel - Emerging Diseases
(CD-Rom)
Learning Intentions
You must know:
The components of a virus
The differences between lytic and lysogenic
cycles
Try These:
1. Explain how capsids and envelopes are
formed
2. Distinguish between the lytic and lysogenic
reproductive cycles
3. Explain why viruses are obligate intracellular
parasites
4. Describe the reproductive cycle of an HIV
retrovirus
5. Describe three processes that lead to the
emergence of new diseases
6. Describe viroids and prions