copyright © 2003 pearson education, inc. publishing as benjamin cummings figure 10.22
TRANSCRIPT
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.22
Viruses
1.Components
2.Infection cycle
3. DNA, RNA viruses
4. Uses of viruses
VIRUSES: GENES IN PACKAGES
Components of a virus (phage)
1. Protein coat = capsid
2.genetic material DNA or RNA3. enzyme
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Components of a virus
Figure 10.18A
Membranousenvelope
RNA
Proteincoat
Glycoprotein spike
• envelope
• capsid
• genetic material
– Ex. flu viruses
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• Phage reproductive cycle
Phage attaches to bacterial cell.
Phage injects DNA.
Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble.
Cell lyses and releases new phages.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Viral DNA may become part of the host chromosome
Phage
New phage DNA andproteins are synthesized
Phage DNA inserts into the bacterialchromosome by recombination
Attachesto cell
Phage DNA
Bacterialchromosome
Phage injects DNA
Occasionally a prophagemay leave the bacterialchromosome
Many celldivisions
Lysogenic bacteriumreproduces normally,replicating the prophageat each cell division
Prophage
Phage DNAcircularizes
LYSOGENIC CYCLE
Cell lyses,releasing phages
Phagesassemble
LYTIC CYCLE
OR
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• Viruses redirect the host cell machinery to make more viruses
• Some animal viruses steal a bit of the host cell’s membrane
Figure 10.18B
VIRUS Glycoprotein spike
Protein coat
EnvelopeViral RNA(genome)
1Plasmamembraneof hostcell
Entry
2 Uncoating
Viral RNA(genome)
3 RNA synthesisby viral enzyme
4 Proteinsynthesis
5 RNA synthesis(other strand)
mRNA
Newviral proteinNewviral proteins
6 Assembly
7
Exit
Template
New viralgenome
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• Most plant viruses have RNA
– Example: tobacco mosaic disease
Plant viruses are serious agricultural pests
Figure 10.19
Protein RNA
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• The deadly Ebola virus causes hemorrhagic fever
– Each virus is an enveloped thread of protein-coated RNA
• Hantavirus is another enveloped RNA virus
• SARS - coronavirus
• Avian flu
Figure 10.20A, B
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– HIV, seen here attacking a white blood cell
Figure 10.22
• HIV is a retrovirus
Invasion of T cell by HIV
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• HIV infection
Figure 10.22x1
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• AIDS quilt
Figure 10.22x2
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Uses of Viruses
• Pest control
• Vaccines
• Anti-cancer treatment
• Gene therapy
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Anti-cancer viruses
Makes use of viral ability to enter only cells of one type
Allows targeting of therapy to tumor cells
Enables identification of small tumor sites
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Coming soon to your local pharmacy!
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Other parasitic particles
• Viroids - infectious RNA (no capsid)
• Prions - infectious protein
– Cellular PrP, prion PrP
– Spongiform encephalopathies cause neural degeneration