VirusesVirusesBiology 2Biology 2

Mr. BeyerMr. Beyer

BacteriophageBacteriophage

What is a Virus?What is a Virus?

Non-cellular Particle (not made of cells)Non-cellular Particle (not made of cells) Genetic Material will be one or the Genetic Material will be one or the

otherother– DNADNA– RNA (retrovirus) makes DNA from RNA RNA (retrovirus) makes DNA from RNA

instead of process where DNA is made instead of process where DNA is made from RNAfrom RNA

Protein Coat (covering around nucleic acid)Protein Coat (covering around nucleic acid)

No independent cellular reproductionNo independent cellular reproduction

No cellular independent cellular metabolic No cellular independent cellular metabolic capabilitiescapabilities

Two Types of Viral Two Types of Viral InfectionsInfections Lytic CycleLytic Cycle

– The virus kills the host cell immediately The virus kills the host cell immediately creating symptoms of the disease…creating symptoms of the disease…fever, pain, swelling, sores….fever, pain, swelling, sores….

Lysogenic CycleLysogenic Cycle– Virus enters the host cell and remains Virus enters the host cell and remains

dormant dormant – Formation of a provirus (the virus DNA Formation of a provirus (the virus DNA

has attached itself to the host DNA)has attached itself to the host DNA)

Lytic CycleLytic Cycle Attachment (Adsorption)Attachment (Adsorption)-Attaches to the host cell -Attaches to the host cell

receptor sitesreceptor sites EntryEntry-The virus injects is Nucleic Acid (DNA or RNA) -The virus injects is Nucleic Acid (DNA or RNA)

into the host cellinto the host cell Provirus FormationProvirus Formation-Virus nucleic acid attaches to host -Virus nucleic acid attaches to host

cell nucleic acid (formation of provirus)cell nucleic acid (formation of provirus) ReplicationReplication-Host cell replicates its DNA with virus DNA -Host cell replicates its DNA with virus DNA

attached. The host cell unwittingly makes virus parts.attached. The host cell unwittingly makes virus parts. AssemblyAssembly- Virus parts are assembled inside the host - Virus parts are assembled inside the host

cell.cell. LysisLysis-Viruses fill the host cell, -Viruses fill the host cell, releaserelease an enzyme that an enzyme that

breaks open the cell membrane and releases the breaks open the cell membrane and releases the viruses, killing the host cell…….symptoms appear in viruses, killing the host cell…….symptoms appear in organismorganism

Lysogenic CycleLysogenic Cycle Attachment (Adsorption)Attachment (Adsorption)-Attaches to the host cell -Attaches to the host cell

receptor sitesreceptor sites EntryEntry-The virus injects is Nucleic Acid (DNA or -The virus injects is Nucleic Acid (DNA or

RNA) into the host cellRNA) into the host cell Provirus FormationProvirus Formation-Virus nucleic acid attaches to -Virus nucleic acid attaches to

host cell nucleic acid (formation of provirus)host cell nucleic acid (formation of provirus) Cell Division-Cells divide, replicating viral DNA Cell Division-Cells divide, replicating viral DNA

with host cell DNA.with host cell DNA. ReplicationReplication-Host cell replicates its DNA with virus -Host cell replicates its DNA with virus

DNA attached. The host cell unwittingly DNA attached. The host cell unwittingly replicating viral nucleic acid.replicating viral nucleic acid.

DORMANCY…… few or no symptoms or the DORMANCY…… few or no symptoms or the disease….. virus remains dormant for a period of disease….. virus remains dormant for a period of time…..eventually the virus will complete its life time…..eventually the virus will complete its life cycle and continue to the lytic cycle, killing the cycle and continue to the lytic cycle, killing the host cellhost cell

Lytic CycleLytic Cycle

VirulenceVirulence

A virus’s ability to cause diseaseA virus’s ability to cause disease– Common cold (low virulence)Common cold (low virulence)– HIV (high virulence)HIV (high virulence)