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Lecture 23

BIO SCI 94 Lecture Notes - Lecture 23: T Helper Cell, Lysogenic Cycle, VirusPremium

Biological Sciences
Course Code
Brad Hughes

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How Are New Virions Assembled?
Enveloped viruses use host endomembrane system→ transport envelope protein
for assembly
How Do Progeny Virions Exit an Infected Cell?
Viruses exit host cell in two ways:
Enveloped viruses bud from cell through cell membrane
Virus takes part of cell membrane and inserted envelope proteins
with them
Nonenveloped viruses burst out of cell
Viruses infect host cells with cell wall and leave by degrading wall
How Are Virions Transmitted to New Hosts?
Virions infect new cells→ new replicative cycle begins
Virus’s long term success depends on ability to spread from host to host
Natural selection prefers viral alleles which allow virus to
Replicate with a host
Spread to new host
Analyzing How Viruses Coexist with Host Cells
All viruses go through replicative growth, some virus can pause replicative
cycle→ go dormant
Bacteriophages, alternate type of infection-lysogeny
No virion produced during lysogeny
Cell divides→ Host’s DNA polymerase replicates viral DNA
Viruses infecting animal cells- dormant state called latency
HIV- latency period
Viral genes not expressed until helper T cell activated by immune
Most effective way to combat viral disease- reduce likelihood of transmission
Where Did Viruses Come From?
Nobody knows how viruses originated
Three hypothesis to explain virus’ origin
Escaped genes hypothesis
Degeneration hypothesis
Rna world origin hypothesis
Origin in Plasmids and Transposable Elements?
Escape genes hypothesis suggests
gene sets physically escaped from bacterial/eukaryotic chromosomes→
Escaped gene become mobile/parasitic; genes encoded information for
Replication at cost of host cell
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