Download 2013 Virus PPT

Biology
Virus Notes
Are Viruses Living or
Non-living?
• Viruses are both and neither
• They have some properties of life
but not others
• For example, viruses can be killed,
even crystallized like table salt
• However, they can’t maintain a
constant internal state
(homeostasis).
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What are Viruses?
• A virus is a noncellular particle made
up of genetic material
and protein that can
invade living cells.
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Viral History
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Discovery of Viruses
•Beijerinck (1897)
coined the Latin name
“virus” meaning poison
•He studied filtered
plant juices & found
they caused healthy
plants to become sick
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Tobacco Mosaic Virus
•Wendell Stanley
(1935) crystallized
sap from sick
tobacco plants
•He discovered
viruses were made of
nucleic acid and
protein
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Smallpox
•Edward Jenner (1796)
developed a smallpox
vaccine using milder
cowpox viruses
•Deadly viruses are
said to be virulent
•Smallpox has been
eradicated in the
world today
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Viewing Viruses
•Viruses are smaller
than the smallest cell
•Measured in
nanometers
•Viruses couldn’t be
seen until the electron
microscope was
invented in the 20th
century
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Size of Viruses
copyright cmassengale
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Viruses
What Is a Virus?
What Is a Virus?
Viruses are particles of nucleic acid, protein, and in
some cases, lipids.
Viruses can reproduce only by infecting living
cells.
What Is a Virus?
T4 Bacteriophage
Head
Tail
sheath
DNA
Tobacco Mosaic
Virus
RNA
Influenza Virus
RNA
Capsid
Tail
fiber
Membrane
envelope
Capsid
proteins
Surface
proteins
What Is a Virus?
A typical virus is composed of a core of DNA or
RNA surrounded by a protein coat.
A capsid is the virus’s protein coat.
Copyright Pearson Prentice Hall
Viral Infection
Viral Infection
Once the virus is inside the host cell, two different
processes may occur.
– Some viruses replicate immediately, killing the host cell.
– Others replicate, but do not kill the host cell immediately.
Viral Infection
Bacteriophage
injects DNA into
bacterium
Bacteriophage DNA
forms a circle
Lytic Infection
Lysogenic Infection
Viral Infection
Lytic Infection
In a lytic infection, a virus enters a cell,
makes copies of itself, and causes the cell to
burst.
Lytic Cycle Review
• Attachment
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Phage attaches by tail fibers to
host cell
Entry/Penetration Phage lysozyme opens cell
wall, tail sheath contracts to
force tail core and DNA into
cell
Biosynthesis/Production Production of phage
DNA and proteins
Maturation/Assembly
Assembly of phage
particles
Release
Phage lysozyme breaks cell wall
copyright cmassengale
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Viral Infection
Viral Infection
Viral Infection
Viral Infection
Lysogenic Infection
Other viruses cause lysogenic
infections in which a host cell makes
copies of the virus indefinitely.
In a lysogenic infection, a virus
integrates its DNA into the DNA of
the host cell, and the viral genetic
information replicates along with the
host cell's DNA.
Viral Infection
Viral Infection
Viral Infection
Viral Infection
Retroviruses
Retroviruses
Retroviruses contain RNA as their genetic
information.
When retroviruses infect cells, they make a DNA copy
of their RNA.
This DNA is inserted into the DNA of the host cell.
Virus Quiz to follow
Virus Quiz
Viruses that contain RNA as their genetic
information are known as
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prions.
oncoviruses.
retroviruses.
bacteriophage.
Virus Quiz
The first type of virus to be studied was the
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bacteriophage.
tobacco mosaic virus.
influenza virus.
AIDS virus.
Virus Quiz
Which of the following statements about viruses
is true?
• Viruses appear similar to bacteria when studied with
a light microscope.
• Viruses display the essential characteristics of living
things.
• Viruses can reproduce independently if they contain
DNA.
• Viruses cannot reproduce unless they infect a living
cell.
Virus Quiz
A virus integrates its DNA into the DNA of the
host cell but remains inactive for a while in
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a lytic infection.
a lysogenic infection.
neither a lytic nor a lysogenic infection.
retroviral infection.
Virus Quiz
Retroviruses are considered unique because
• they have RNA in their capsid and not DNA.
• they have DNA in their capsid and not RNA.
• after infection of a host cell, their RNA makes
DNA.
• after infection of a host cell, their DNA makes
RNA.
END OF SECTION