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Viruses
What is a virus?
• a non-cellular
particle
• Invades living
cells
• discovered in
1935
Polio virus
Viral Structure
• Composition: 2 Parts
– A core of Nucleic
Acid (DNA or RNA)
– Capsid: protein coat
Retroviruses: contain RNA
Influenza
(Flu) Virus
HIV Structure
Viral RNA
Core Proteins
Protein Coat
Lipid Envelope
Spikes
Shape: Large variety
• Rod, sphere, cube, helix,
dodecahedron
Rabies
Herpes
Tobacco
Mosaic
Bacteriophage
Measles
Size: .05 – 2 micrometers
1µm
Staphylococcus
E. coli
Eukaryotic Cells Prokaryotic Cells Viruses
(10-100 µm)
(0.2-10 µm)
(0.05-0.2 µm)
Virus Specificity
• viruses infect only
specific host cells
– http://www.youtube.co
m/watch?v=Rpj0emEGS
hQ
• act as parasites
• H1N1
– http://www.youtube.co
m/watch?v=lFl3FRNpU4
E&NR=1
Viral Infection
• viruses are completely
dependent on a living
host cell
• 2 methods of infection:
– Lytic
– Lysogenic
Rabies
Lytic Infection
•
Attachment to host cell
Lytic Infection
• Injection of viral
DNA into host cell
Lytic Infection
• Synthesis of
more viral DNA
and protein
• Assembly of new
viruses
Lytic Infection
• Lysis (destruction)
of the host cell;
release new
viruses.
Lysogenic Infection
similar to lytic infection, except virus does not
reproduce and lyse host cell right away
Lysogenic Infection
•
Attachment and
injection
Lysogenic Infection
• Prophage: viral
DNA becomes
part of the
host cell's DNA
Lysogenic Infection
• Replication: viral DNA is
replicated when the host cell
divides
Lysogenic Infection
• Activation of prophage: caused by
environment factors (illness, stress, etc.)
HIV Replication
Virus attaches to receptor
Viral RNA enters the cytoplasm
Viral RNA moves
to cytoplasm
Virus makes DNA
using viral RNA
DNA enters nucleus
& chromosomes
HIV Replication
Viruses bud from
plasma membrane
Viral proteins &
RNA assembled
Viral proteins made
Herpes Replication
Viral envelope merges
with nuclear membrane
Virus enters cell
Viral DNA released
& enters nucleus
Herpes Replication
New viruses assembled get
envelope from nuclear membrane
Viral proteins
enter nucleus
New viruses
leave the cell
Origin of Viruses
• Probably a piece of
nucleic acid escaped
from its host cell but
can replicate
parasitically within it
• Viruses resemble their
host cells more than
other viruses
Prions
• Misfolded proteins that cause infection
• Cause Normal proteins to mutate
• Infect nerve cells in brain causing them to
burst
CreutzfeldtJacobs
Transmissible Spongiform
Encephalopathies
Scrapie
Mad Cow
Kuru