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Microbiology: VirusesLearning Outcomes:
1. Describe the basic structure of a virus.
2. Evaluate the evidence used to classify viruses as living or non-living
3. Describe the major steps in viral reproduction; compare and constrast the lytic and
lysogenic cycles.
4. Describe the body’s basic defenses against a viral attack.
5. Give examples of ways to reduce the chance of contracting a viral disease.
6. Define and five examples of viral specificity.
7. Evaluate the effects of virulence on human health.
8. Explain how viruses transfer genetic material between cells.
Text: Chapter 19. *This is required reading.
Introduction to Viruses
-Viruses are not cells, so they are not placed in any of the kingdoms of living organisms.
-They are composed of a _______________ core of either DNA or RNA, and a
_______________ coat called a capsid. They may have an envelope composed of a membrane
from their host combined with viral glycoprotein.
-Viruses are called obligate parasites because: _____________________________________
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-Viruses are very small. They are 2 to 0.2 micrometers in size. This is comparable to a large
protein molecule.
Biology 11 Enriched: Viruses Page 1
*See some creative Virus artwork at the Met.
-The diagram below is of a typical influenza virus. It belongs to a type of viruses that
are surrounded by a membrane envelope.
-Label: RNA, protein coat, membranous envelope and glycoprotein spike.
-How do enveloped viruses get
their envelopes? How are the envelopes useful?
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Biology 11 Enriched: Viruses Page 2
Are Viruses Alive?
Comparison of Virus and Bacteria Traits
Characteristics of Life Bacteria Viruses
Possesses Nucleic Acid
Consists of a Cell
Metabolism
Respond to Stimuli
Multiply
Evolve
Viral Reproduction
Viruses are specific to the cells that they attack. Why
is this?
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Biology 11 Enriched: Viruses Page 3
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Bacteriophage Life Cycles
-Bacteriophages are viruses that attack
_______________ and they have two types of life
cycles (or two parts to their life cycle).
Biology 11 Enriched: Viruses Page 4
Why have bactetriophages not exterminated all bacteria? (text 385)
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What is a latent virus?
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Retroviruses
Below is a diagram of a retrovirus life cycle. What is meant by the term “retrovirus”?
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What is the enzyme in the retrovirus
that creates a DNA molecule from the
RNA?
______________________________
Give an example of a viral disease
caused by a retrovirus?
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Biology 11 Enriched: Viruses Page 5
The History of AIDS (http://fohn.net/history-of-aids/ )
-Read the quote from an article about the history of AIDS.
“While the origin of the AIDS epidemic has been clarified, an explanation for why the
epidemic arose in the mid-20th century, and not before, remains a matter of speculation."
Chimpanzees are frequently hunted for food, especially in West-Central Africa, and we
believe that HIV-1 was introduced into the human population through exposure to blood
during hunting and field dressing of these animals," says Hahn. She further believes that
while incidental transmissions of chimpanzee viruses to humans may have occurred
throughout history, it was the socio-economic changes in post-World War II Africa that
provided the particular circumstances leading to the spread of HIV-1 and the
development of the AIDS epidemic. "Increasing urbanization, breakdown of traditional
lifestyles, population movements, civil unrest, and sexual promiscuity are all known to
increase the rates of sexually transmitted diseases and thus likely triggered the AIDS
pandemic," adds Hahn.
Prions
Prions are slow acting, virtually indestructible infectious proteins that cause brain
diseases in mammals, such as Mad Cow Disease. These misfolded proteins causes
normal proteins inside of brain cells to also misfold. In doing so, it causes the brain and
spinal cord to deteriorate and affects the cow’s behaviour and nervous system.
Plant Viruses and Viroids
Plants can also be affected by viruses. One type of plant
virus is called viroids:
-Viroids are small circular RNA molecules that use plant
cell enzymes to replicate themselves.
Biology 11 Enriched: Viruses Page 6
a) Tobacco Virus; b) Pea Mosaic Virus
-Viroids cause errors in the system controlling plant growth.
*Complete the Development of Virology Lab to learn more about plant viruses.
Biology 11 Enriched: Viruses Page 7
