Download Viruses

Figure 10.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
VIRUSES: GENES IN PACKAGES
Viruses
1. Components
2. Infection cycle
3. DNA, RNA viruses
4. Uses of viruses
Components of a
virus
(phage)
1. Protein coat =
capsid
2.genetic material
DNA or RNA
3. enzyme
Components of a virus
• envelope
Membranous
envelope
• capsid
• genetic material
RNA
– Ex. flu viruses
Protein
coat
Glycoprotein spike
Figure 10.18A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Attaches
to cell
Bacterial
chromosome
Phage DNA
Cell lyses,
releasing phages
Phage injects DNA
Many cell
divisions
Occasionally a prophage
may leave the bacterial
chromosome
LYTIC CYCLE
Phages
assemble
Phage DNA
circularizes
LYSOGENIC
CYCLE
Prophage
Lysogenic bacterium
reproduces normally,
replicating the prophage
at each cell division
OR
New phage DNA and
proteins are synthesized
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Phage DNA inserts into the bacterial
chromosome by recombination
Glycoprotein spike
VIRUS
• Viruses redirect
the host cell
machinery to
make more
viruses
• Some animal
viruses steal a bit
of the host cell’s
membrane
Protein coat
Viral RNA
(genome)
Plasma
membrane
of host
cell
Envelope
1
Entry
2
Uncoating
3
RNA synthesis
by viral enzyme
Viral RNA
(genome)
4
Protein
synthesis
5 RNA synthesis
(other strand)
Template
mRNA
New
viral proteins
protein
6
New viral
genome
Assembly
Exit
7
Figure 10.18B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Plant viruses are serious agricultural pests
• Most plant viruses have RNA
– Example: tobacco mosaic disease
Protein
Figure 10.19
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
RNA
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
– HIV, seen here
attacking a white blood
cell
Figure 10.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• HIV is a retrovirus
Invasion of T cell by HIV
• HIV infection
Figure 10.22x1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• AIDS quilt
Figure 10.22x2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Uses of Viruses
• Pest control
• Vaccines
• Anti-cancer treatment
• Gene therapy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings