The document provides an overview of viruses, describing their structure, replication cycles, and various types, including RNA and DNA viruses. It discusses immune responses to viral infections and recent discoveries in virology, highlighting the existence of large viruses and their uses in genetic research. Additionally, it covers influenza, its causes, symptoms, transmission, and treatment options.

1. Ezkare
Presentation
Viruses are much smaller than bacteria. They were not visible until the
invention of the electron microscope. A virus has a simple structure. It
has no internal cellular structure, no cell wall or cell membrane, just
the protein coat that holds the string of nucleic acid.
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2. Definition of Virus
A virus is a tiny parasite which can infect the living
organisms. Can copy itself inside their cells. Made
only of a nucleic acid + a protein coat. Usually the
nucleic acid is RNA; sometimes it is DNA.
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3. Characteristic of Virus
Infectious particles, causing many types of disease;
Contain nucleic acid core RNA or DNA;
Surrounded by a protective protein coat;
Viruses have the following characteristics:
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4. Genom
There are a many genomic structures in viruses. As a group they have more structural genomic
diversity than plants, animals, archaea, or bacteria. There are millions of different types of
viruses, but only about 5,000 of them have been described in detail.
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5. Replication Cycle
Viral populationsdo not grow through cell division, because they do
not have cells. Instead, they use the machinery and metabolism of a
host cell to produce many copies of themselves, and they assemble
(put together) in the cell.
Genetic Materials and Replication
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6. Attachment is a specific binding between viral capsid proteins and
specific receptors on the host cellular surface.
Penetration follows attachment: Virions (single virus particles) enter the
host cell through receptor-mediated endocytosis or membrane fusion.
Uncoating is a process in which the viral capsid is removed: Thismay be by
degradation by viral enzymes or host enzymes or by simple dissociation.
Replication of viruses involves multiplication of the genome.
Following the structure-mediated self-assembly of the virus particles, some
modification of the proteins often occurs.
Viruses can be released from the host cell by lysis, a process that kills the
cell by bursting its membrane and cell wall.
6 Basic Stages
in The Life
Cycle of Virus

7. RNA Viruses
DNA Viruses
Reverse
Transcribing Viruses
Genetic
Material and
Replication
The genetic material within virus particles,
and the method by which the material is
replicated, varies considerably between
different types of viruses.
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8. RNA Viruses
Replication usually takes place in the cytoplasm. RNA viruses can be placed into four different groupsdepending on their
modes of replication. All RNA viruses use their own RNA replicase enzymes to create copies of their genomes.
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9. DNA Viruses
The genome replication of most DNA viruses takes place in the cell's nucleus.
Most DNA viruses are entirely dependent on the host cell's DNA and RNA
synthesising machinery, and RNA processing machinery. Viruseswith larger
genomes may encode much of this machinery themselves.
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10. Reverse
Transcribing Viruses
Reverse transcribing viruses with RNA genomes
(retroviruses) use a DNA intermediate to replicate.
Those with DNA genomes (pararetroviruses) use an
RNA intermediate during genome replication.

11. Innate Immune System Adaptive Immune System Evading Immune System
HostDefence
Mechanisms
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12. Innate Immune System
The body's first line of defence against viruses is the innate immune system. This has cells and other mechanisms which defend the host
from any infection. The cells of the innate system recognise, and respond to, pathogensin a general way.

13. Adaptive
Immune System
Vertebrates have a second, more specific,
immune system. It is called the adaptive
immune system. When it meets a virus, it
produces specific antibodies that bind to
the virus and render it non-infectious. Two
types of antibodies are important.

14. Evading
Immune System
Not all virus infections produce a protective immune to the
response. These persistent viruses evade immune control by
sequestration (hiding away); blocking antigen presentation;
cytokine resistance; evading natural killer cell activity; escape
from apoptosis (cell death), and antigenic shift (changing
surface proteins).

15. Evolution
Viruses donot belong to any of the six kingdoms. They do not meet all the
requirements for being classified as a living organism because they are not
active until the point of infection. However, that is just a verbal point. The
origins of viruses in the evolutionary history of life are unclear: some may
have evolved from plasmids – piecesof DNA that can move between cells –
while others may have evolved from bacteria.

16. Break
Time!
Break for 30 minutes
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17. Recent Discoveries
A recent project discovered nearly 1500 new RNA viruses
by sampling over the 200 invertebrate species. "The
research team... extracted their RNA and, using next
generation sequencing, deciphered the sequence of a
staggering 6 trillion letters present in
the invertebrate RNA libraries".
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18. LargestViruses
Pithovirus
Megavirus
Pandoravirus
Mimivirus
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19. Pithovirus
Pithovirus is a genus of giant virus
which infects amoebae. It is a double-
stranded DNA virus, and is a member
of the clade of large DNA viruses.
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20. Pandoravirus
Pandoravirus is a genus of very large
viruses, with the largest genomes of any
viral genus. Its genome, with 1.9 to 2.5
megabases of DNA, is twice as large as
that of Megavirus.
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21. Megavirus
Megavirus is a virus with a single identif
species, Megavirus chilensis (MGVC). It was
is phylogenetically related to or the name
Mimivirus (APMV).

22. Mimivirus
Mimivirus is a new extra-large virus. It is either a viral genus with a single
species, Acanthamoeba polyphaga mimivirus (APMV), or it is a group
of phylogenetically-related large viruses (MimiN).

23. Uses of Virus
Viruses are used widely in cell biology. Geneticists often use viruses as vectors to introduce
genes into cells that they are studying. This is useful for making the cell produce a foreign
substance, or to study the effect of introducing a new gene into the genome.
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24. Definition of Influenza
It is caused by several different viruses (see: RNA virus), which is why
people can have the flu more than once.. The name influenza comes
from Italian: influenza, meaning "influence".
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25. Flu Transmissions
and Symptoms
Symptoms include cough, sore throat, muscle aches and pains, fever,
headache, and rarely vomiting and diarrhoea. Influenza can also lead to
other diseases, such as pneumonia. This makes it especially dangerous
to young children and elderly people.
Human Influenza can pass from one person to another very easily. It is
most commonly spread by the microscopic droplets of mucus and fluid
that are sent intothe air when the sick person coughsor sneezes.

26. Changes in the Influenza Virus
Small changes that happen as flu is passed from one person to another is the most common way flu
viruses change. This is the main reason that people can catch the flu every year. Another way that the flu
can change is when a person or animal catches two different flu viruses. The two viruses can exchange
some of their genetic information, which can create a brand new flu that nobody has ever caught before.

27. Fever and chills
Symptoms
Cough
Nasal Congestion
Runny Nose
Sneezing
Sore Throat
Hoarseness
Ear Pressure
Earache
Muscle Aches

28. Treatment
People with the flu are advised to get plentyof rest,
drink plentyof liquids, avoid using alcohol and
tobacco and, if necessary, take medications such as
acetaminophen (paracetamol) to relieve the fever
and muscle aches associated with the flu. Children
and teenagers with flu symptoms (particularly
fever) should avoid taking aspirin during an
influenza infection (especially influenza type B),
because doing so can lead to Reye's syndrome, a
rare but potentially fatal disease of the liver.

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30. ThanksFor Watching
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