Transcript Viruses and Bacteria

Viruses
Virus-
an infectious
agent made up of a core
of nucleic acid and a
protein coat
viruses
are NOT cells,
they are non-living
a
virus does NOT have a
nucleus, a membrane, or
cellular organelles.
viruses
do have organized
structural parts
Structure and Shape
•Viruses
are tiny particles that are not alive
•Viruses are about 50-100 times smaller than
the smallest bacterium
Bacteriophage
 Bacteriophage
- Virus
that infects a bacterium
All viruses have at least 2 parts:
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Core of nucleic acid (DNA/RNA)
Capsid - protective protein coat around
the core of nucleic acid. The capsid
protects the nucleic acid core from its
environment.
Additional parts may include:
Envelope - an
additional protective
coating usually made of
lipids, proteins, and
carbohydrates.
**These are only found in
viruses that infect
animal cells (i.e. flu
virus)!**
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Additional parts may include:
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Spiked projections that
bind to the membrane
of the cell being
infected.
Examples of Viruses
Attachment to a host cell.
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Host cell – A living cell that a virus
enters and begins to take over
(through replication)
A virus cannot live and replicate
without a host cell
**living cells host viruses!**
Viral Attachment to Host Cell
*Fits like a jigsaw puzzle or two spaceships docking.
What happens when a virus attaches to
a host?
Lytic Cycle
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The viral replication process that
immediately kills a host cell.
A virus attaches to a host cell.
The virus injects its DNA/RNA into
the cell.
Lytic Cycle Cont.
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The virus commands the host cell to
make copies of the virus.
New viruses are assembled.
The cell bursts (lyses) and the
viruses are released and ready to
attack other host cells.
Viral replication- The Lytic Cycle
Lysogenic Cycle
A
type of replication
cycle in which a virus
Does Not immediately
kill a host cell.
Lysogenic Cycle
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A virus attaches to a host cell and
injects its DNA into the cell.
The viral DNA inserts itself into a
host’s chromosome.
The host cell divides, replicating the
viral DNA along with its own DNA.
A stimulus allows the viral DNA to
separate from the cell’s chromosome
and enter the Lytic cycle (ex. stress).
Lysogenic Cycle
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Without a stimulus, the viral DNA
stays in the cell’s chromosome.
A viral DNA segment that is inserted
in a bacterial cell’s chromosome is
called a provirus
Lysogenic Cycle
Special Types of Viruses
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Retrovirus - a virus that contains an
RNA core that replicates by first
transcribing its RNA into DNA (ex. HIV).
This is the reverse of what happens
normally during replication.
Prion – somewhat like viruses, cause
disease. Instead of nucleic acid they
have a protein molecule that can cause
disease in animals (ex. mad cow disease).
Special Types of Viruses
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Viroid – made of a single strand of
pure RNA only, no protein coat.
These infect plants.
Vaccines
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Vaccination - is the process of
injecting a person with a harmless
weakened or dead form of the virus.
Your immune system builds up
antibodies for this virus and the
next time you come in contact with
it, your immune system is able to
defend itself. Ex. chicken pox, small
pox, polio, measles
Treating Viruses
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Antibiotics – DO NOT GET RID OF
VIRUSES! They only work on bacterial
infections!
Antiviral drugs – can make disease
symptoms milder but only work on
certain viruses and do NOT get rid of the
virus. They also must be taken
IMMEDIATELY after symptoms begin in
order to have a chance to work at all.
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Ex – Tamiflu for H1N1.
Treating Viruses
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Viral suppression drugs – Keep a virus
from entering the lytic cycle so it doesn’t
replicate (i.e. you don’t have an
outbreak). The virus is still in your body
but is at really low levels, so low that it
might not even show up on a test. These
medications must be taken daily and you
can still get an outbreak even while
taking them. You can still pass on the
virus whether or not you are having an
outbreak.
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Ex – Valtrex for herpes
Important Information About Viruses
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Herpes Simplex Virus – Includes
oral herpes (Type 1) and genital
herpes (Type 2). These viruses can
be passed to ANY mucous
membrane and you can pass oral
herpes to the genital/anal region,
and genital herpes to the oral and
eye regions.
Important Information About Viruses
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HIV/AIDS – HIV stands for Human
Immunodeficiency Virus; AIDS stands for
Acquired Immune Deficiency Syndrome.
AIDS is NOT a virus. HIV is the virus that
causes AIDS. HIV weakens your immune
system so that your body cannot fight off
diseases it should normally be able to.
AIDS is stage 4 of HIV infection and is
diagnosed after your immune system has
been substantially damaged. People with
HIV/AIDS do not die from it; they die
from another infection due to their
compromised immune system.
Virus Naming
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Viruses are not named in the same
way as organisms- Why?
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Some are named for the diseases they
cause
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Ex- rabies viruses, polioviruses
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Adenovirus- affects the adenoid tissue in
back of throat (common cold)
Some for the organ they infect
Virus Naming Cont.
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Viruses have a genus and species
name
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Genus name- Ends in virus
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Some are given code numbers to
distinguish between similar viruses.
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T1, T2, ect.
 T stand for type
Questions
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1. How does the viral nucleic acid enter
the bacterial host cell?
The virus attaches to the host cell and injects the nucleic
acid into the cell
2. Describe how new viruses are produced
in the host cell.
After injecting the nucleic acid into the cell, the cell’s
organelles are “tricked” into using the viral nucleic acid to
make and assemble new viruses
Questions
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3. Explain why viruses would cease to
exist if they replicated via the lytic cycle
only.
In the lytic cycle the virus kills the host cell very rapidly and
spreads to other nearby cells, killing them shortly thereafter. It is
possible for the virus to be killed off my the host organism’s
immune system and not spread to another organism.
4. What is a provirus? What cycle would
you find a provirus?
A provirus is a viral DNA segment that is inserted in a bacterial
cell’s chromosome, this occurs in the lysogenic cycle
Questions
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5. How does the lysogenic cycle
change to the lytic cycle?
The lysogenic cycle enters the lytic cycle when a stimulus,
usually stress related, triggers the provirus to enter the
lytic cycle thereby causing the organism to show
symptoms.
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The End