Download Unit 4 – Student Guided Notes

Unit 4 – Student Guided Notes
Structure of Viruses
Discovery of the Virus
Many human epidemics were well documented and
observed in history, but
________________________________________
_________________. The following 3 discoveries shaped our knowledge of
viruses and disease
Jenner's Experiment (1700's).
_____________________________________________________________
_____. He discovered that milkmaids who contracted cowpox and recovered
________________________________________________
_________________________________________________. On the 14 May
1796, a young milkmaid called Sarah Nelmes came to see him with blister like
sores. ___________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
______________________________________________ which he would
inject later. To test his hypothesis Jenner
approached a local farmer and explained that if
his theory was correct, the man's son James
would never contract smallpox. Surprisingly, the
farmer agreed. Jenner made two small cuts on
James's left arm. He then poured the liquid from
Sarah's cowpox sores into the open wounds which
he bandaged. James got sick with cowpox but
once recovered and exposed to smallpox he did not become ill with the smallpox
disease. This was an extremely risky experiment, but James lived and Jenner had
found a way to prevent smallpox.
Jenner called his idea " _______________________" from the word vaccinia
which is latin for cowpox. Jenner also introduced the term _______________.
Tobacco Mosaic Virus (TMV)
_____________________________________
_____________________________________
_____________________. The virus caused a
blotchiness on the leaves of tobacco crops
making them unmarketable and worthless.
Solving this problem was a priority as tobacco
was an important crop in these times.
A German scientist, Adolf Meyer, suggested that Mosaic disease was contagious
and proposed that the infectious agent was an unusually small bacterium that
could not be seen with a microscope. He tested his hypothesis by successfully
transmitted the disease by spraying sap from infected plants onto the healthy
ones. Using a microscope, he examined the sap and was unable to identify a
microbe.
In 1897 a Dutch microbiologist, Martinus Beijerinck, _____________________
_____________________________________________________________
_____________________________________________________________
____________________He ruled out the theory that a filterable toxin such as
bacteria caused the disease by demonstrating that the infectious agent in
filtered sap could reproduce.
So what exactly is a Virus???
A virus is a ___________________________________________________
_____________________________________________________________
_____________________________________________________________
________________________________________.
Viruses _______________________________________________________
and because of this feature are considered _____________________. In fact,
viruses are ____________________________________________________.
Viruses affect all types of cells, ____________________________________
_____________________________. For example, bacteriophages ________
____________________________________, the tobacco mosaic virus
infects only plants and the rabies virus only infects mammals. Viruses can be
even more specific than this. Some human viruses even specialize in specific
tissue. Human immunodeficiency virus (HIV) affects specific types of white
blood cells and the polio virus _____________________________________
____________________________. Viruses are so specific because the capsid
binds with _______________________ in the host cell's plasma membrane. If
the receptors do not match then the virus cannot attach. Once attached to a
cell, the virus _____________________________________________ within
the host cell for its own purposes.
Viruses and their relationship to host cells has led to the hypothesis that the
_____________________________________________________________
_____________________________________________________________
_________. This statement suggests that viruses evolved after cells
developed. If so, this means that new viruses are developing all the time. New
viruses can develop _____________________________________________
__________________________. This means that antibodies produced by the
body can work against one type of virus, but might not recognize the new
mutated virus.
Virus Structure
There are ______________________________
_____________________________ to viruses:
1. Proteins forms a structure called the coat or
__________________. The capsid acts as the
protective covering for the nucleic acid it
contains. The proteins in the virus’ capsid must
match the protein markers on the surface of the
membrane of the cell it is trying to invade. As
previously stated this feature is responsible for
viral specificity.
2. Nucleic acids - All viruses contain either DNA
or RNA, _______________________________
______________________________________.
This means that instead of using DNA to control
the activities of the host cell ______________________________________
_____________________________________________________________
_______________________________________ which can then direct the
activities of the host cell to reproduce viral particles.
There are many different shapes and types of viruses but, because of the
similarities between bacteriophages and animal cell viruses, the bacteriophage
can be viewed as a model for animal cell viruses. The diagram above is of a
typical bacteriophage.
Head Region - _________________________________________________.
The Tail - The Plug is a ___________________________________________
_____________________________________________________________
- The ______________________________________________________ to
a bacterial host cell.
Viral Replication
_________________ do not reproduce, they _________________________
_____________________________________________________________
____. Host cells ________________________________________________
__________________________________________________. Viruses are
specific to a particular host cell because part of the capsid binds to the
receptor on the host cell's plasma membrane in a lock and key fashion. The
virus then will inject its viral nucleic acid into the host cell and ____________
_____________________________________________________________
_____________________________________________________________
________________________________________.
Replication of Bacteriophages
Bacteriophages are viruses that are parasitic to bacteria. These phages must
use bacteria to replicate. Phages have two types of cycles. In _____________
____________________________ the virus is replicated within the host cell
resulting in ____________________________________________________
releasing all of the newly formed virus particles. In _____________________
the __________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
____________________________________________________ sometime
in the future.
Reproductive Cycles
Lytic Cycle
There are five key stages to the lytic cycle.
1. _________________________ - Capsid combines with the bacteria's
receptor in a lock and key fashion.
2. _________________________ - Enzymes from the virus start to eat away
the bacterial cell wall and will inject its viral DNA into the bacterial cell.
3. _________________________ - At this stage the virus inactivates the
bacterial genes and takes over the metabolic functions to produce copies
of DNA and produce the capsid.
4. _________________________ - During this stage, the viral DNA and
capsids are put together.
5. ________________________ - Lysosomes are made and produce hydrolytic
enzymes to eat a hole in the cell wall of the bacteria. At this time, the
cell will lyse and the newly formed viruses will leave the host cell.
Lysogenic Cycle
_________________________________________________________, the
_________________________________________________________, but
____________________________________________________________.
During the lysogenic cycle, the phage becomes a prophage that is integrated
into the host genome (DNA). At a later time, the phage may start the lytic
cycle. When a virus is latent i.e.
_______________________________________, it is called a prophage.
_____________________________________________________________
_____________________________________________________________
_________________________________________________.
Examples of lysogenic Viruses: Herpes, Hepatitis, HIV
Retroviruses
Retroviruses are viruses that have the
_____________________________.
These viruses contains an enzyme
called ________________________
___________________. This enzyme
_____________________________
_____________________________
(in other words, it allows the RNA to
make DNA).
____________________________________________________________
__________________________________, which can hide in the host's DNA.
_____________________________________________________________
_____________________________________________________________
_________________________________. An example of a retrovirus is HIV
and some that cause cancers.
Are Viruses Alive?
What are the characteristics of life? How do we define whether something is
living or not? Living things….
1. _______________________________________________.
2. _______________________________________________.
3. Require a constant energy supply.
4. ________________.
5. ____________________________________.
6. _______________________________________________.
7. Contain enzymes.
8. Can move.
So, are viruses living or nonliving? The following table gives evidence to support
each theory.
Living
Non-living
Viruses have DNA or RNA and protein.
No non living thing carries nucleic
acid
_____________________________
_____________________________
(slightly different variations)
___________________________
___________________________
Viruses display continuity
Viruses do not grow
Viruses have the ability to reproduce
One generation follows another
Viruses contain enzymes
_____________________________
_____________________________
Viruses do not eat
___________________________
___________________________
Viruses do not reproduce on their
own. Viruses are parasitic
Viruses do not move
Viruses _________________________________________________things
as they do not exhibit many of the characteristics of life.
Viruses are not classified in the classification system because they are ______
___________________ and should not be classified with organisms that are
cellular. Viruses are generally smaller than 200 nm in diameter and can be
crystalized.
Viral Diseases
We now know that viruses are considered pathogens that cause disease. We
know that many of these diseases are specific to a particular type of host cell
and that viruses are not considered living as they require this host cell to
reproduce. We also know that viruses cause a large variety of diseases.
Some __________________________________________ while _________
_____________________________________________________________
_____________________________________________________________
_________________________________________________. Some new
antiviral medications are being developed but are only used in special
circumstances at this time.
Viral pathogens are newsworthy.
You may recognize the ones in the
list below. You will notice that
there is a lot of variety in the
structure and function of these
viruses. This variety is not a surprise
as viruses have been evolving for a
very long time along with the cells
they infect.
The photo above is a micrograph of an Adenovirus that causes the common
cold. You know the symptoms.
Photos below are of Smallpox which causes high fever and the formation of
small blisters on the skin. _______________________________
_____________________________________________________________
(1970's). Let's hope it stays that way as vaccinations ceased in the 1980's.
Photos below are of the Polio virus which is transmitted through direct contact
and feces and the IRON LUNG. Polio destroys nerve cells and causes paralysis. It
may well be the next viral disease eliminated by a vaccine.
Hanta Virus
Hanta virus _____________________________
______________________________________
_______________. The result is ___________
______________________________________
_____________________________________.
There is no vaccine so avoid contact with mice!
West Nile Virus
West Nile virus is transmitted_____________________
___________________________________________.
The virus ___________________________________
(encephalitis). There is no vaccine so avoid contact with
mosquitoes. _________________________________
___________________________________________.
HIV (Human Immunodeficiency Virus)
_____________________________________________________________
_____________________________________________________________
___________________________________________.
Transmission of the virus is _______________________
_________________________. It is estimated that 50
million people are infected worldwide. There is no
vaccine but there are effective drugs that can slow the
disease but not cure it.
Ebola
Ebola was first recognized in 1976. It is
______________________________
_________________________________________
_________________________________________
_________________________________________
________________________. There is no vaccine
but outbreaks have been controllable (so far). This
virus is often the source of inspiration for movies such
as "Outbreak"
Preventing Viral Diseases
Antibiotics are _________________________________________________.
Antibiotics are designed to disrupt the metabolism of organisms. They work on
bacteria but ___________________________________________________
__________________________________________________. The best way
to stop viral infections is to prevent them from getting into the body to find a
host cell.
The term ________________________ is often used to describe the degree
to which a particular pathogen is infectious.
The human body has 3 major lines of defense against disease caused by
viruses and bacteria.
The Primary line of defense is made up ___________________________.
These barriers include: skin, hair, earwax, boogers, saliva, stomach acid, cilia
in the throat, mucus, tears, oil, etc.
The first line of defense is almost always enough to stop invaders. However,
_____________________________________________________________
_________________________________________ and the pathogens are
able to move inside the body.
When this happens _____________________________________________
_____________________________________________________________
_____________________________________. These are the secondary and
tertiary lines of defense.
Secondary line of defense is made up of Phagocytic white blood cells that
deactivate and then engulf the viruses destroying them. When the secondary
line of defense cannot destroy the invaders the
Tertiary line of defense is activated. The tertiary line of defense is made up
of ___________________________________________________________
_____________________________________________________________
_____________________. The antibodies find the chemical signal the
antigen is excreting and latches on to it. Different pathogens have different
markers. Antibodies are made specific to each marker. B-Cells (____________
________________________________) release antibodies. (They tag the
incoming virus for destruction). ____________________________________
_____________________________________________________________
_________________________________________________. Viruses are
destroyed later by phagocytic white blood cells.
Additional defense against viruses
____________ are produced by virus _______________________________
_____________________________________________________________
_____________________________________________________________
_____________. Interferons slow viral infection and allow WBCs and
antibodies to respond.
And
__________________________ are chemicals that ____________________
(cell-eating WBCs) in the blood. Pathogens are engulfed and digested by the
phagocytes.
Achieving Immunity
_______________________________ are used to produce immunity against
pathogens. It is the process of infecting a person with a __________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
_______________________________________________.