viruses,viroids and prions-part 1 au10-1
TRANSCRIPT
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VIRUSES, V IR O IDS A ND
PRIONS
Chapter 13
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L iving Cells or Nonliving Entities?
A . Inert outside the Host
B . Nucleic acids become active onceinside the host
C . Obligate Intracellular Parasites
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Vir ion Structure
1. Non-enveloped or Naked viruses
Nucleocapsid
2.
Enveloped virusesIn addition to Nucleocapsid,some virusescontain lipid
envelope,spikes
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Vir ion Structure
1.
Nucleocapsid
A . Nucleic acid:
DN A/RN A , ds/ss,
ci rcular/linear/fragmented
B . Capsid: protein coat
Capsomere arrangement
and shape
2. Envelope: lipid
3. Spikes
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Bacteriophages: Complex Viruses
Tail fibers,
involved in
attachment.
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Figure 13.1
Virus Sizes
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General Characteristics of V iruses
Obligatory intracellular parasites Contain DNA or RNA
Contain a protein coat
Some are enclosed by an envelope
Some viruses have spikes
Most viruses infect only specific types ofcells in one host
Host range is determined by specific hostattachment sites and cellular factors
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General Characteristics of V iruses
MultiplicationInsidelivingcells using host cell
machinery
Regulation of vi ral synthesis
Very few viral enzymes
Viruses are in charge
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How do Viruses differ from bacteria?
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Virus Interactions with Host Cells
1. Productive Infection
Lysis of Host cel l : V irulent phage T4
2. Latent Infection
Te
mpe
rate
phage
Lambda
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The Lytic Cycle
Attachment: Phage attaches by tail fibers tohost cell
Penetration: Phage lysozyme opens cell
wall; tail sheath contracts to force tail coreand DNA into cell
Biosynthesis: Production of phage DNA and
proteins Maturation: Assembly of phage particles
Release: Phage lysozyme breaks cell wall
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Lytic Cycle of a T-Even Bacteriophage1
2
3
Figure 13.11
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4
Figure 13.11
Lytic Cycle of a T-Even Bacteriophage
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Figure 13.10
A Viral One-Step Growth Curve
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The Lysogenic Cycle
1.
Temperate Phage Lambda causesLatent Infection/Lysogeny
2. Host = Lysogen
3. Replication of Lambda: Lytic or Lysogenic
1. Attachment
2. Penetration
3. Prophage
4. Gett ing out of lysogeny
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Figure 13.12
The Lysogenic Cycle
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Advantages of Lysogeny to the
Host
1. No direct lysis of the host
2.
Immunity3. Lysogenic Conversion: Lysogenic host
acquires new properties
4.
Transduction