biology virus notes. 2 are viruses living or non-living? viruses are both and neither they have some...
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Biology
Virus Notes
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Are Viruses Living or Are Viruses Living or Non-living?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 What are Viruses?Viruses?
•A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.
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Viral Viral HistoryHistory
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Discovery of VirusesDiscovery 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 VirusTobacco 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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SmallpoxSmallpox•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 VirusesViewing Viruses•Viruses are Viruses are smaller smaller than the smallest cellthan the smallest cell•Measured in Measured in nanometersnanometers•Viruses couldn’t be Viruses couldn’t be seen until the seen until the electron microscopeelectron microscope was invented in the was invented in the 2020thth century century
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Size of VirusesSize of Viruses
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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?
Head
Tail sheath
DNA
T4 Bacteriophage Tobacco Mosaic Virus
Influenza Virus
RNA
Membrane envelope
Tail fiber
RNA
Capsid proteins
Capsid
Surface proteins
Copyright Pearson Prentice Hall
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.
Viral Infection
Viral InfectionOnce 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 InfectionBacteriophage 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.
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• Attachment 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
Lytic Cycle ReviewLytic Cycle Review
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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
RetrovirusesRetrovirusesRetroviruses 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
• prions.• oncoviruses.• retroviruses.• bacteriophage.
Virus Quiz
The first type of virus to be studied was the • bacteriophage.• tobacco mosaic virus.• influenza virus.• AIDS virus.
Virus QuizWhich 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
• 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.
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