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Viruses
Discover of viruses
Martinus Beijerinck: Dutch scientist who said that
disease is caused by tiny particles in juice.
Called them viruses. Latin for poison.
Wendall Stanley: isolated crystals of the tobacco
mosic virus.
Dmitri Ivanovski: for tobacco mosiac in liquids
extracted from infected plants.
VIRUSES
Virus: infectious particle that contains DNA or
RNA surrounded by a protein coat that can only
reproduce in a host cell.
Latin for “poison”.
Viruses Are viruses alive? Scientists are still arguing!!!
At the boundary of life, between the macromolecules
(which are not alive) and the prokaryotic cells (which
are), lie the viruses and bacteriophages (phages).
These twilight creatures are parasites responsible for
causing many diseases in living things (herpes and
HIV in humans, for example).
Viruses are found everywhere.
Viruses consist of a core of nucleic acid, either DNA
or RNA, and a protective coat of protein molecules and
sometimes lipids.
In isolation, viruses and
bacteriophages show none of the
expected signs of life. They do not
respond to stimuli, they do not grow,
they do not do any of the things we
normally associate with life.
Strictly speaking, they should not be
considered "living" organisms at all.
However, they are more complex than
a lifeless collection of macromolecules
and they do show one of the most
important signs of life: the ability to
reproduce at a fantastic rate
but only in a host cell.
Characteristics of Living Things
Respond to stimulus: virus respond when a cell is
near and attaches.
Cells: Not cells as we know them
Adapt: The viruses do mutate to become stronger but
only in a host cell.
Reproduces: only in a host cell
Energy: Uses energy of the host
DNA: Yes they do have their own
Grow and develops: Only in host
Viruses are parasites that can only perform certain
characteristics in host cells.
Host: The cell that the virus attaches and uses their
DNA and resources.
PARTS OF A VIRUS
Viruses consist of a core of nucleic acid,
either DNA or RNA, and a protective coat of
protein molecules and sometimes
lipids(capsid).
CAPSID: Protein coat
Surrounding the DNA.
Size and Shape of Viruses
Viruses come in all shapes sizes. You can only
see them with a microscope.
3 shapes of viruses
1.Enveloped – round with spikes( flu viruses)
2.Helical – Long narrow coiled shape( rabies)
3.Polyhedral- many sides(foot and mouth disease)
The different proteins that make up the
capsid determines the shape of the virus.
Attacking the host
The size and shape of a virus determines which
cells or host they can attack.
Attacking Host
The virus will attach itself to the host cell. It will then shoot
its DNA into the host cell. The virus is a parasite that uses
the host cell for its energy and reproduction. It is a little
different if it is a bacteria cell or eukaryotic cell.
Difference between a bacteriophage and a
virus
Bacteriophages attack bacteria (prokaryotes)
viruses attack eukaryotic cells(have a nucleus).
Viruses and bacteriophages invade cells and use the
host cell's machinery to synthesize more of their own
macromolecules.
Once inside the host the bacteriophage or virus
will either go into a Lytic Cycle destroying the host cell during
reproduction.
or
It will go into a Lysogenic Cycle - a
parasitic type of partnership with the cell
Lysogenic Cycle
The virus COMBINES its DNA with the host DNA producing a
Prophage. The cell is not destroyed. As new cells are made, it
will be the virus and not host cell. Cell not destroyed.
Both:
http://www.youtube.com/watch?v=wLoslN6d3Ec
http://www.youtube.com/watch?v=gU8XeqI7yts
LYSOGENIC CYCLE
The Lysogenic Cycle
Lytic Cycle
In the lytic cycle, the virus takes over the hosts DNA and
grows its own. It grows its own DNA and new viruses.
The virus uses the energy of the host cell. When it is full,
the host cell explodes and releases new viruses.
http://www.youtube.com/watch?v=wLoslN6d3Ec
LYTIC CYCLE
The Lytic Cycle
A provirus is a DNA virus that has been inserted into a host
cell chromosome.
A retrovirus injects the enzyme, reverse transcriptase into the cell
to copy viral RNA into DNA.
HIV is a retrovirus injecting the enzyme, reverse
transcriptase into the cell to copy viral RNA into DNA.
Viruses are host specific – a protein on the surface of the virus
has a shape that matches a molecule in the plasma membrane
of its host, allowing the virus to lock onto the host cell.
HIV doesn’t target just any cell, it goes right for the cells that
want to kill it. “Helper" T cells are HIV's primary target. These
cells help direct the immune system's response to various
pathogens.
HIV undermines the body's ability to
protect against disease by depleting T
cells thus destroying the immune system.
The virus can infect 10 billion cells a day,
yet only 1.8 billion can be replaced daily.
After many years of a constant battle, the body
has insufficient numbers of T-Cells to mount an
immune response against infections. At the point
when the body is unable to fight off infections, a
person is said to have the disease AIDS.
It is not the virus or the disease that ultimately
kills a person; it is the inability to fight off
something as minor as the common cold.
The vaccine is administered. It contains weakened or
dead forms of the disease
1.The immune system identifies these foreign substances
(viruses and bacteria), also known as antigens.
2.Once antigens are identified, the immune system
develops proteins that circulate in the blood. These
proteins are called antibodies. They fight the infection
by killing the antigens. Antibodies are made by white
blood cells called lymphocytes, also known as B cells.
The main purpose of B cells is to create antibodies to
fight infection.
3.The body stockpiles these antibodies so they are
available to fight off the disease if exposed later on.
Unfortunately, antibodies are disease-specific, so
previously acquired chickenpox antibodies will be
useless if faced with other diseases.
Jenner was operating on the now widely
accepted principle that once a person catches
a certain disease, he or she is immune to it for
the rest of their life. For example, once you've
had the chickenpox, it's extremely unlikely that
you'll ever catch it again. This is because your
body, when exposed again, will recognize the
disease and fight it off. The beauty of vaccines
is that they help the body develop diseasefighting abilities without making you sick.
Vaccines accomplish this amazing feat by
tricking the body into believing it already has
the full-blown disease. Here are the steps in
this process, known as the "immune
Vaccine-preventable Diseases
Anthrax
Cervical Cancer
Diphtheria
Hepatitis A
Hepatitis B
Haemophilus influenzae type b
Human Papillomavirus
Influenza
Japanese encephalitis
Lyme disease
Measles
Meningococcal
Monkey pox
Mumps
Pertussis
Pneumococcal
Polio
Rabies
Rotavirus
Rubella
Shingles
Smallpox
Tetanus
Typhoid
Tuberculosis
Varicella
Yellow Fever
Source: CDC
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