biology virus notes. 2 are viruses living or non-living? viruses are both and neither they have some...

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

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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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