Transcript Viral Reproduction

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Read Viral Replication
We will take notes on this today!
Take jot notes on Viruses and Human Health
 Three important points or more!
 Define Antibiotic and Vaccines
Answer 5 questions on Influenza
Viruses and Human Health
Most viral infections are difficult to treat, they are not
destroyed by antibiotics.
ANTIBIOTICS - inhibits the growth of or destroys
microorganisms.
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Some viruses can remain dormant for years before
symptoms appear
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Certain viruses cause cancer by adding specific genes
to an infected cell.
VACCINES - liquid preparations of dead or weakened
viral or bacterial cells that stimulate the body’s immune
system to fight back.
Influenza (FLU)
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Usually considered to be more annoying than dangerous
Spread by direct contact and can live for hours in dry mucus
First host: cells in the upper respiratory tract
Soar throat, congested lungs, chills, fever, pain, sweating…
Contagious 1 day before symptoms appear, up to seven
days after.
Incubation 1 – 4 days
Last up to 2 weeks
Influenza vaccine can be 90% effective
Viral Reproduction
February 5, 2008
Viral Reproduction
Viruses can reproduce only within a host cell because:
a) lack specific enzymes and ribosomes
(necessary to make new cores & capsids)
b) have no energy of their own
(needed to synthesize their parts)
There are 2 modes of viral reproduction
Lytic Cycle: all DNA viruses reproduce this way
Lysogenic Cycle: mostly RNA viruses use this cycle
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Difference between
RNA and DNA viruses
RNA viruses
 common cold
 Unstable they change their
protein coat and “fool” the
immune system
DNA viruses
 Chickenpox
 Stable and are the same
throughout
Why do we need a Flu shot once a year?
The Lytic Cycle
February 5, 2008
SBI3U - A.Y. Jackson S.S.
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1. Attachment
1a. Attaches to host cell by its receptor sites
1b. Injects
its core
(DNA)
into the
host cell
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2. Synthesis
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Viral DNA stops host protein synthesis
Viral protein coats are made
Viral DNA is also replicated 100’s of times using cell
machinery
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3. Assembly
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Capsids surround the viral DNA cores
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100's of virus particles are assembled in the
cytoplasm of the host cell
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4. Release
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Host cell is destroyed (bursts) as 100’s of
viruses are released
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Each virus now infects a neighbouring cell
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The Lytic Cycle
•All DNA viruses reproduce with the lytic cycle and are called
virulent (capable of causing disease & extremely infectious)
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The Lysogenic Cycle
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RNA viruses cannot take over the host cell machinery
directly
They must first change their RNA to DNA.
To do this they have a special enzyme called reverse
transcriptase.
Because this is a reverse process RNA viruses are
called retroviruses.
Retroviruses are especially lethal to their hosts because
the viral DNA produced by this enzyme can splice into
the host chromosome and stay dormant or latent for
months or years.
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The Lysogenic Cycle
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When each host cell divides, it also copies the viral DNA
'hiding' within its own chromosome.
During this dormant period, the host's immune system
does not 'see' the viral DNA and produces no antibodies
against it.
The host feels no symptoms, but carries the disease and
may infect others.
Examples of diseases caused by retroviruses are AIDS,
genital Herpes and cold sores.
Some unknown stimulus will 'trigger' the viral genes to
become active, take over the cell's protein synthesis and
continue as in the lytic cycle.
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Steps Of The Lysogenic Cycle
viral RNA
lysogenic
cycle
reverse transcriptase
viral DNA
viral DNA splices into host chromosome & becomes dormant
dormancy period of variable length
viral DNA activated and takes over host protein synthesis
lytic cycle
viral DNA is copied 100's of times
host ribosomes are used to make viral protein coats
newly made viruses are assembled and released by destroying their host cell
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(DO NOT WRITE)
The Lysogenic Cycle
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Still unclear what "triggers“ the dormant viral DNA to
enter lytic cycle.
Hormones and high stress levels (adrenaline) often
associated with activation
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The Lysogenic Cycle
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Homework
Read “Sex Slaves for Science” article
Answer questions # 1 – 11
April 8, 2016
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