Viroids, Prions, Viruses, and
Bacteria
Chapter 20
Thinking Question #1
(Partner Activity)
A. What is the difference between a bacteria and a virus?
B. Are both considered cells? Why or why not?
C. Of the following diseases which are caused by viruses or
bacteria?
-Measles
-Chicken pox
- Aids,
-Botulism
-Tuberculosis
-Bubonic Plague
-Syphilis
-Polio
-Flu
-Mumps
- Lyme disease
- Strep throat
- Common Cold
D. Can antibiotics cure all of these diseases, why or why not?
Viruses
• Viruses are extremely small, non-living, disease-causing
•
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pathogens that have the ability to infect any organism
including bacteria.
Viruses are composed of a protein coat (capsid) with
either viral DNA or viral RNA.
Viruses may only replicate in a living organism. They do
not have the ability to reproduce on or in a non-living
surface.
Flu virus http://science.nationalgeographic.com/science/photos/influenza/flu-virus.htm
l
Thinking Questions #2
• Thinking Question #2: What is a
pathogen?
Viruses
• Viruses are so small, that they
were not discovered until the
end of the 19th century when
they were trying to find the
pathogen that caused tobacco
mosaic disease (TMV).
• Once discovered, it was called
a virus, which is Latin for
“poison.”
• In 1935, Wendell Stanley finally
purified and crystallized the
TMV virus.
What Are Viruses?
• If you recall, Rosalind Franklin, the same one whose
•
photo 51 of crystallized DNA was “taken” by Watson &
Crick, pursued other research interests and began
working on trying to figure out the anatomy of a virus.
This is what she and others found. 1.)The virus has a protein coat or capsid.
 2.) A virus may contain either DNA or RNA, but not
both.
 3.) Some viruses have an additional membrane or
envelope.
Structure of Influenza Virus
Viral Structures
Figure
1
An array of
viruses. (a) The
helical virus of
rabies. (b) The
segmented
helical virus of
influenza. (c) A
bacteriophage
with an
icosahedral
head and helical
tail. (d) An
enveloped
icosahedral
herpes simplex
virus. (e) The
unenveloped
polio virus. (f)
The icosahedral
human
immunodeficien
cy virus with
spikes on its
envelope.
Classification of Viruses
• Viruses can be classified according to the
following characteristics.
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1.) Whether or not they contain DNA or RNA
2.) Their shape
3.) What they infect
4.) Their genetic make-up
5.) The type of disease that they may cause
The group of viruses that infect bacteria are
called bacteriophages.
Bacteriophage
Thinking Question #2
• Thinking Question #3: How does a virus
get into a cell?
Virus Movie
• Virus Animation
How Does A Virus Get Into A
Host Cell
• Viruses “know” which organisms to infect because
•
they try to attach to specific receptor sites, which are
usually proteins that are found on the cell
membranes of an organism.
Once the virus has recognized and attached to the
specific organism’s cell membrane receptor site, the
virus gains entry by one of two ways
1. Endocytosis
2. Virus injects its DNA or RNA into the cell of the
organism.
• http://www.courses.fas.harvard.edu/~bi
otext/animations/viralinfection.html
Virus Entry
Lytic vs. Lysogenic Cycle
• Once inside the cell, one of two things can happen.
 1.) The virus can lay dormant (asleep) inside the cell
and not cause the organism to get sick. This is called
the lysogenic cycle. Diseases that ‘keep showing up’
such as herpes could be considered lysogenic.
 2.) The virus hijacks the cell’s normal cellular functions
and tricks the cell into making more viruses. This will
eventually kill the cell and cause more viruses to be
released. This is called the lytic cycle. Diseases that
begin and end over a short period of time such as a
cold could be considered lytic.
Lysogenic Cycle
Animation
• Lysogenic Cycle Animation
• http://www.courses.fas.harvard.edu/~biote
xt/animations/lysogeny.html
Lytic Cycle
http://www.web-books.com/MoBio/Free/Ch1F1.htm
Lytic Cycle
• Lytic Cycle Animation
• http://www.courses.fas.harvard.edu/~biote
xt/animations/lyticcycle.html
Thinking Question #4
• Thinking Question #4: What do you think
causes a virus that is in the lysogenic cycle
to become lytic (Example: Someone that
has not had a herpes outbreak for years
suddenly has one)
Thinking Question #3
• Thinking Question #5: How do you get a
virus? How are viruses spread?
Viral Transmission
• You cannot catch a viral disease from simply touching or
•
sitting on a surface. The only ways that you can catch a
viral disease is from direct contact, an injection,
inhalation, or spreading infected body fluids into a cut,
your mouth, your nose, or your eyes.
Many recent studies have shown that by simply washing
your hands prior to eating, rubbing your nose, or rubbing
your eyes, you can exponentially reduce your chances of
getting a viral infection.
http://www.foodlink.org.uk/factfile_c.asp?file=2&chapter=2
http://www.bma.org.uk/ap.nsf/Content/viralrespiratorydisorders~spread
http://www.cnn.com/2007/HEALTH/10/31/flu.dos.donts/index.html
http://www.sciencedaily.com/videos/2005/1212-fighting_cold_and_flu_germs.htm
http://www.southcoast.org/24/flu.html
http://www.wcu.edu/4995.asp
http://www.health.gov.sk.ca/influenza-schools-parents
Some of the diseases which
are caused by viruses:•
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AIDS
The common cold
Ebola
Hepatitis A and B
Influenza or the flu
Mumps
Polio
Rabies
Smallpox
Lab Activity
• Pass It On
Virus Prevention
• Inactivated Vaccine: made of virus particles that have
•
•
been killed and cannot replicate. The virus capsid
proteins are still intact enough to be recognized by
immune system and evoke a response
Attenuated Vaccine: Vaccine which uses “live” but
weakened/altered virus so it is less virulent. Preferred
because these vaccines last longer
Antiviral Drugs: drugs that interfere with viral nucleic
acids and viral reproduction used to treat HIV, herpes,
influenza
Thinking Question #6
• Are there other types of pathogens besides
viruses and bacteria?
Prions
• Pathogens discovered in the 1980s and have since
•
•
been shown to be involved a variety of diseases,
such as Kuru, Mad Cow, and other brain illnesses.
Prions are proteins that “have gone bad.” They find
their way into the brain and cause the proteins in the
brain to change shape.
These newly shaped proteins then create plaques or
hard parts in the brain. (The brain is not supposed to
have these plaques.).
http://jackson.ifas.ufl.edu/bse.htm
http://www.ens-newswire.com/ens/jul2006/2006-07-10-03.asp
http://scienceblogs.com/retrospectacle/2007/02/basic_concepts_prions.php
http://www.sciencemag.org/feature/data/prusiner/245.dtl
http://www.biologie.uni-duesseldorf.de/Institute/Physikalische_Biologie/Research/Topics/addinformation2
http://www.cnspathology.com/
Healthy Brain tissue - Note few ‘holes.’
Fig 1: Histopathology shows spongiform changes in brain of A sporadic
CJD, B new variant CJD, C Kuru and D BSE (pictures A-C Hans
Kretzschmar, M殤chen, D Martin Groschup, Insel Riems)
• http://highered.mcgrawhill.com/sites/dl/free/0072835125/126997/a
nimation44.html
• http://www.youtube.com/watch?v=H2Ouxl_
GNjA
Viroids
• These are newly discovered infectious agents
•
that are single pieces of RNA that lack a
capsid
Several have been identified as plant
pathogens while only one so far has been
identified as a human pathogen (hepatitis
delta).
http://www.biologie.uni-hamburg.de/bzf/mppg/agviroid.htm
Fig. 2: Symptoms of viroid diseases: A: potato spindle tuber
on tomato, B: avocado sun blotch, C: chrysanthemum stunt,
D chrysanthemum chlorotic mottle
http://www.virtualology.com/
virtualmuseumofnaturalhistory/
halloftaxonomy/viruses/viroids.org/
Bacteria
• The ancestors of these organisms are
•
considered to have been some of the first life
forms on Earth given the fossil record.
Thinking Question #7: Review
A. Are bacteria prokaryotic or eukaryotic, why?
http://www.ucmp.berkeley.edu/bacteria/cyanofr.html
Bacteria differ from
eukaryotes in at least 7 ways.
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No organelles
Cell size: (1u-5u)
Unicellular
Plasmids (single circular piece of DNA)
Binary fission
Flagella (single flagellum in bacterial cells) &
Pilli (small outer growths enable bacteria to
attach to cells or other surfaces
Metabolic diversity
Bacterial Flagella & Pilli
Metabolic Diversity
• Bacteria have the ability to metabolize either
under the following conditions:
 Anaerobic (no oxygen)
 Aerobic (with oxygen)
• They may be:
1. Photosynthetic autotrophs
2. Chemoautotrophs
3. Heterotrophs (decomposers)
Photosynthetic bacteria
• Photosynthetic Bacteria use energy
from sunlight to make food
• Four types based on the photosynthetic
pigments they contain
1. Purple non-sulfur
2. Cyanobacteria
3. Anaerobic purple sulfur
4.Anaerobic green sulfur
Chemoautotrophic Bacteria
• Chemoautotrophic Bacteria: use inorganic
molecules such as ammonia, hydrogen
sulfide, and methane to make their own
food.
• Live in soil produce chemicals such as
nitrates and phosphates, which help
fertilize plants.
Heterotrophic Bacteria
Bacteria
• Most bacteria are heterotrophs
• Bacteria, along with fungi, are
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the main decomposers for most
ecosystems.
Anaerobic fermentation (bacteria
help produce fermented food like
cheese, vinegar & sour dough
bread
.
Yogurt
Fungi
Thinking Question #8
• Thinking Question #5: Where are
bacteria found?
http://www.nsf.gov/news/special_reports/sfs/index.jsp?id=life&sid=ext
Bacteria Bacteria Everywhere
• Since they have adapted a variety of
different ways to obtain food, they can
be found almost anywhere on Earth.
• Often warm moist environments
• 80-100 F 90% water
Thinking Question #9
• Thinking Question #9 : So why do
bacteria make us feel so sick? What are
they doing inside our bodies?
So Why Do Bacteria Make us
Feel So Sick
• Some bacteria produce toxins. These
chemicals are what cause us to have
nausea, diarrhea, and/or vomiting when we
are infected with bacteria.
• Food poisoning
So Why Do Bacteria Make us
Feel So Sick
• Some can not only produce toxins, but
they can also secrete enzymes which
destroy our normal cell’s functions.
• A human’s normal inflammatory response,
which includes a fever, a human’s immune
system, vaccinations, and prescribed
antibiotics may be effective means to
control the bacterial infection.
Examples of infections caused
by bacteria are:•
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Anthrax
Bubonic plague
Cholera
Dental cavities
Lyme disease
Tuberculosis
Typhus
Acne
Food poisoning
Bacteria come in three shapes.
• Bacillus or Rodshaped
• Coccus or round
• Spirillum or
spiral
http://universe-review.ca/F11-monocell.htm
Bacterial Forms
• Some bacteria
aggregate in specific
ways.
 Strepto- bacteria group
together into long
filaments.
 Staphylo- bacteria
group together into
clusters.
 Diplo: two
 Tetrad: four
http://www.ncl.ac.uk/dental/oralbiol/oralenv/tutorials/streps.htm
http://nbsp.sonoma.edu/resources/presentations/derekpres/05Microbe%20lecture/sld003.htm
Bacterial Killers
• Thinking Question # 10: So what kills
bacterial cells other than antibiotics?
Bacterial Killers
• Ammonia: disrupts bacterial cell
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membrane
Alcohol: breaks down proteins
Chlorine: destroys chemical bonds in
bacteria
Iodine: stops proteins from working
Penicillin: stops cell wall formation