21.2 Viral Replication

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21.2 Viral Replication

• All viruses replicate only inside host cells, but
  the details of the process vary among viral groups

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Stepped Art
Table 21-2, p. 336
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Bacteriophage Replication

• Lytic pathway
• Under direction of viral genes, the host makes an
  enzyme that lyses and kills the cell
• Lysogenic pathway
• Virus enters a latent state
• Host replicates viral genes and passes them on to
  descendents before entering lytic pathway

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A1 Viral DNA is inserted into host chromosome by
viral enzyme action.
A Virus particle binds, injects genetic material.
A2 Chromosome and integrated viral DNA are
replicated.
E Lysis of host cell lets new virus particles
escape.
Lytic Pathway
Lysogenic Pathway
D Accessory parts are attached to viral coat.
A3 Cell divides recombinant DNA in each
daughter cell.
B Host replicates viral genetic material, builds
viral proteins.
A4 Viral enzyme excises viral DNA from
chromosome.
C Viral proteins self-assemble into a coat
around viral DNA.
Fig. 21-4, p. 337
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Replication of an Enveloped DNA Virus

• Example Herpes
• Viral envelope fuses with host membrane viral
  DNA enters host cytoplasm
• Viral DNA enters nucleus, directs synthesis of
  new viral DNA and proteins
• New viral particles are assembled and enveloped
  in host nuclear membrane
• New viral particles exit cell by exocytosis

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Prokaryotic Reproduction

• Prokaryotic chromosome
• A circular, double-stranded DNA molecule
• Prokaryotic fission
• DNA replicates parent cell divides in two

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Prokaryotic Fission
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Horizontal Gene Transfers

• Conjugation
• Transfer of a plasmid (non-chromosomal DNA)
  between prokaryotic cells via a sex pilus
• Transduction
• Transfer of prokaryotic genes via bacteriophages
• Transformation
• Prokaryotic genes acquired from the environment

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Conjugation
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