Download Viruses & Microorganisms

Viruses & Microorganisms
By Dr. Rick Woodward
5/23/2017
1
Today’s Agenda:
a. Journal Question: Identify three
diseases transmitted in your
saliva.
*1. Lecture III: Viruses &
Microorganisms
2. Video: The Spreading Menace
3. Homework: Read Chapter 25
(pp.486 – 500)
5/23/2017
2
Did you know?
Spotlight: Gym Equipment
5/23/2017

The threat: A 2006 study in the Clinical
Journal of Sports Medicine found
rhinoviruses (instigators of the common
cold) on 63 percent of the gym equipment
at the fitness centers they tested.

Researchers also discovered that weight
equipment was contaminated
significantly more often than aerobic
equipment (73 percent versus 51 percent).
Even worse, the study found that
disinfecting the equipment twice a day
didn't do anything to lower the virus count.

The Solution: Avoid touching your face
between sets, since most colds are
transmitted through hand-to-nose contact.
And make sure to pack an alcohol-based
hand sanitizer in your gym bag.
3
Did you know?
Spotlight: Restaurant Menu
The threat: Ever see anybody wash a
menu?
- A recent study in the Journal of Medical
Virology reports that cold and flu viruses
can survive for 18 hours on hard
surfaces. If it's a popular joint, hundreds of
people could be passing their germs on to
you.
5/23/2017
- The Solution: Never let the menu touch your
plate or silverware as you ponder the wine
list, and wash your hands after you order.
But how do you escape the bathroom
without touching the door handle? Palm a
spare paper towel after you wash up, and
then use it to grab the handle. Execute this
trick properly and nobody needs to know
4
how much you fear germs.
Did you know?
Spotlight: Flight Attendants




5/23/2017
The threat: Flight attendants are exposed to
dozens of sniffling and coughing passengers
and the surfaces they touch.
When attendants need a restroom break, they
head into the same latrine you use.
Now consider that when Charles Gerba, Ph.D.,
coauthor of The Germ Freak's Guide to Outwitting
Colds and Flu, tested commercial-jet bathrooms,
he found that surfaces from faucets to
doorknobs were contaminated with E. coli.
Given all that germ exposure, it's no surprise that
the Journal of Environmental Health Research
recently revealed that you're 100 times more
likely to catch a cold while flying than on the
ground.
The Solution: Pack a green-tea pill. In a 2007
University of Florida study, people who took a
450-milligram green-tea supplement twice a day
for 3 months had a third fewer days of cold
symptoms. Try Immune Guard ($30 for 60 pills,
immune-guard.), the brand used in the study.
5
Did you know?
Spotlight: Lemon Wedge in your Water
-The threat: In a 2007 study from the
Journal of Environmental Health,
nearly 70 percent of the lemon
wedges smashed into restaurant
glasses contained diseasecausing microbes.
-Researchers ordered drinks at 21
different restaurants, securing 76
lemons. Testing revealed 25 different
microorganisms lingering on the
lemons, including E. coli and other
fecal bacteria.
5/23/2017
6
What is a virus?
1. Viruses are not organisms.
2. Viruses have no cytoplasm and
no organelles.
3. Virus is the Latin word for
poison.
5/23/2017
7
What is a virus?
4. Viruses are quite small. (Smaller
than bacteria)
a. They cannot be visualized with
the light microscope.
5/23/2017
8
Size Comparison:
Bacteria versus Virus
5/23/2017
9
What is a virus?
5. Viruses are particles capable of
reproduction at the expense of
specific host cells
a. A virus needs chemicals and
ribosomes of the healthy cells it
invades in order to reproduce.
b. Virus particles are called
“virons.”
5/23/2017
10
What is a virus?
Recall: Prions are the
causative agent in
“Mad Cow” disease.
6. Viruses are capable
of invading only
specific cells.
5/23/2017
11
Prions in Mad Cow Disease
5/23/2017
12
What is a virus?
7. Viruses have a nucleic
acid component.
a. Either DNA or RNA
5/23/2017
13
Virus Structure
1. Viruses are composed of:
-An outer protein coat that
encloses a nucleic acid.
a. A capsid or protein coat.
5/23/2017
14
Virus Structure
b. Nucleic Acid (DNA or RNA)
c. In some instances, an outer
membranous envelope.
5/23/2017
15
Virus Structure
d. The viral genome can be
coated with proteins forming
different viral shapes:
(1) Spherical (AIDS virus)
(2) Polyhedral head with tail
fibers
(Bacteriophage)
5/23/2017
16
Virus Structure
(3) Polyhedral (Polio virus)
(4) Rod-Shaped (Tobacco mosaic virus)
5/23/2017
17
5/23/2017
18
Viral Cycles
1. When a virus invades
a cell, new viruses
are produced.
2. The invaded cell is
called a host because
it provides materials to
the virus.
5/23/2017
19
The Lytic Cycle
(Search & Destroy Mission)
1. A virus can identify and
infect a potential host
cell only if part of the
viral coat can match a
specific receptor site
on the membrane
surface of the host
cell.
5/23/2017
20
Lytic Cycle
(1) e.g. HIV can only attack
certain white blood cells
called T-Lymphocytes in the
immune system.
(Recall: The immune system
protects you from getting
sick by destroying pathogens,
which are disease causing
agents)
5/23/2017
21
Lytic Cycle
(1) a. T-Lymphocytes have a
specific protein receptor
site called CD4.
b. CD4 is believed to be the
site where HIV’s viral
protein GP120 attaches.
5/23/2017
22
HIV Viron
5/23/2017
23
Lytic Cycle
(2) e.g. The tobacco
mosaic virus can only
invade and attack the
leaf of the tobacco plant.
-Viruses are very specific
when it comes to finding a
host.
5/23/2017
24
Search & Destroy Mission of an
Active Virus (Using a DNA Virus)
First the virus has to find
a viable host
(Virus recognizes
appropriate receptor site)
1. Attachment to host
5/23/2017
25
Search & Destroy Mission of an
Active Virus (Using a DNA Virus)
2. Entry (Inject nucleic acid
into host cell).
3. Viral DNA takes over and
replication begins.
a. Host DNA is destroyed
and the new viral nucleic
acids and proteins are
made.
5/23/2017
26
Search & Destroy Mission of an
Active Virus (Using a DNA Virus)
4. Formation of new virus
particles.
(Virons are assembled)
5/23/2017
27
Search & Destroy Mission of an
Active Virus (Using a DNA Virus)
5. Host cell breaks open
(lysis); New virus
particles are released.
Lysis & Release
5/23/2017
28
5/23/2017
29
Search & Destroy Mission of an
Active Virus (Using a DNA Virus)
A. Facts about an “Active Virus.”
(1) This entire process (Steps 1-5) is called the
lytic cycle
(2) Lysis can occur as quickly as
20 minutes after attachment!!!
(3) During the lytic cycle, a virus takes over the
metabolic activities of its host cell, makes many
copies of itself, and destroys the cell.
(4) Antibiotics ( e.g. Penicillin) do not kill viruses.
5/23/2017
30
Some Examples of
Active Viruses:
1. Influenza (Flu) Virus
a. Avian (Bird) Flu Virus
2. HIV
3. Hanta Virus
4. Ebola Virus
5/23/2017
31
Influenza (Flu) Virus
5/23/2017
32
Avian (Bird)
Flu Virus
5/23/2017
33
5/23/2017
34
HIV Virus
5/23/2017
35
Hanta Virus
5/23/2017
36
Ebola Virus
5/23/2017
37
West Nile Virus
5/23/2017
38
Birds that carry the West Nile Virus
5/23/2017
39
Lysogenic Viruses
Provirus
1. After attachment and entry,
viral DNA may sometimes
become integrated into the
host cell’s chromosome.
a. When this occurs, the viral
DNA is known as a provirus.
b. A provirus can also be
called a latent virus.
5/23/2017
40
Lysogenic Viruses
2. When a cell that contains a provirus is
exposed to environmental factors
like:
(1) X-rays
(2) Chemicals
(3) UV light from the sun (sunburn)
(4) Stress
(5) Extreme changes in temperature
*Any of these factors can trigger
a provirus to become active.
5/23/2017
41
Lysogenic Viruses
3. Provirus triggered to become
active:
(1) The viral DNA take over the
machinery.
(2) New viruses are manufactured.
(3) The host cell lysis occurs.
(4) The new viruses are released
to invade other cells.
-The pattern of reproduction is
called the lysogenic cycle.
5/23/2017
42
Some Examples of
Lysogenic Viruses:
1. Herpes: The gift that keeps giving.
(The gift you don’t want!)
5/23/2017
43
Summary of Viral Cycles
5/23/2017
44
RNA Viruses
A. Most viruses containing
RNA go through the same
lytic and lysogenic cycles
as DNA viruses.
5/23/2017
45
RNA Viruses
1. RNA viruses that enter the
lysogenic cycle are unusual.
2. They contain RNA, but their
host cell’s genetic material
is DNA.
5/23/2017
46
RNA Viruses
3. How can viral RNA attach
to the host’s DNA to
become a provirus?
-Answer: These viruses
contain a unique enzyme
called reverse
transcriptase, which
reverses the normal
transcription process.
5/23/2017
47
Using Reverse
Transcriptase
1. Instead of transcribing DNA to RNA,
reverse transcriptase transcribes
RNA to DNA.
2. Once the DNA has been transcribed, it
can be double stranded by replication
and join the host’s chromosome.
3. Because the viruses perform
transcription backwards, these
viruses are called retroviruses. (retro
means backward)
4. The virus that causes AIDS is an
example of a retrovirus.
5/23/2017
48
Next Topic: Bacteria
5/23/2017
49