BIO SCI 94 Lecture Notes - Lecture 23: T Helper Cell, Lysogenic Cycle, VirusPremium
Course CodeBIO SCI 94
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How Are New Virions Assembled?
● Enveloped viruses use host endomembrane system→ transport envelope protein
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
○ 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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