Transcript 254166_Virus_powerpoint.PPT

VIRUSES
HISTORY
• *The word “virus” from
Greek ois meaning
“poison”
• -were suspected as agents
of disease in the late
1800’s
• -1545- viral hemorragic
fever. 15 million dead
• influenza pandemic of
1918-19 killed 20 million
worldwide
• Ebola 2013 West Africa
• 11,300 dead
How big are
viruses?
• The nanometer;
• 1nm =1/1000th um,
or
• 1/1millionth of a mm
• Polio virus = 20nm
smallpox = 250nm
All viruses have 2 essential
features and 1 optional feature
• **1. A nucleic acid;
either DNA or RNA
(but not both)
• The nucleic acid may
be helical, a closed
loop, or a long strand
2nd feature
• 2. A capsid: a protein
coat called which
surrounds the nucleic
acid.
• The HIV capsid is
composed of 2000
interlocking proteins
Envelope
An envelope:A lipid
layer surrounding the
capsid.
It is derived from host
cell membranes.
May help in avoiding
host cells immune
system.
Envelopes are perforated
w/Glycoroteins that
assist in binding to
receptor sites
Wendell Stanley 1935
• First to see a virus using an electron microscope
• Tobacco Mosaic Virus
• Stanley realized it was not a cell so assumed
viruses were chemicals
Shapes viruses may be
Icosahedron
helix
Hairpin;loop
Bricks
spheres
Viruses –
Living or
Nonliving??
• Viruses are:
NOT cellular in origin;
DO NOT have a membrane
DO NOT have organelles
DO NOT have cytoplasm.
DO NOT use energy (eat)
DO NOT grow or develop
DO NOT produce wastes
DO replicate(reproduce),
but it requires the host cells
energy and materials (stuff)
to make new viral particles
LYTIC CYCLE: Means of viral
replication
• A. virus attaches to host cell (attachment)
• B. virus injects its DNA/RNA into host cell
(infection)
• C. viral DNA/RNA spliced into host DNA
(integration)
• D. copies of viral DNA/RNA produced by the host
cell (replication)
• E. new viral particles leave the host cell (lysing
and budding)
Step 1. Attachment
(by endocytosis)
Virus attaches to host via proteins on its surface (receptor
site)
nd
2
Infection:
Viral RNA or DNA is injected into the host cell.
3rd Integration:
DNA “spliced” into host DNA via enzymes.
4th Replication:
Cell makes copies of the viral DNA.
DNA synthesis
Lysing and budding:
virus releases enzymes that rupture the cell membrane
allowing new viral particles into the blood
Lytic Cycle
• Results in the death of
the host Cell
• Attachment/Adsorption
• Injection/Entry
• Replication
• Assembly
• Release (lysis)
Lysogenic cycle
• Virus incorporates its DNA into the host
The host replicates viral DNA during normal
cell division.
At some point the virus becomes lytic
Lysogenic cycle
Virus incorporates its DNA into the host
The host replicates viral DNA during normal cell division.
At some point the virus becomes lytic
Lysogenic
Cycle
• Virus DNA is
replicated when
the cell divides
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Attachment
Injection
Integration
Cell Multiplication
Each new cell
contains a copy of
the viral DNA
Lytic vs. Lysogenic Cycle
• If lytic cycle destroys host too soon, the
virus will not be completely assembled
• Lysogenic cycle is “silent killer” and body
does not realize infected
• In either case, if there are no hosts, there
are no viruses
Viruses That Infect Bacteria
• Bacteriophages
• Extensively studied
because its replication
cycle is similar to
other human viruses;
HIV and influenza
Small Pox
• Group Poxviruses
• DNA
• Complex brick-shaped
• Enveloped
Retroviruses$$
HIV the retrovirus
• Spherical in shape
• Double strand RNA core
• Surrounded by a lipid
envelope perforated with
proteins.
• Uses the enzyme reverse
transcriptase to convert
RNA to viral DNA
• Must accomplish 5 steps
to successful replication.
1) Attachment; via
surface proteins
2) Infection;Penetration
and shedding of
protein coat
3) Sabotage; viral nucleic
acid is incorporated
into cells nucleic acid.
4) Transcription;
proviral DNA is made
by the cell.
5) Lysing/budding;new
infectious viral
particles are released.
5 Steps to
Successful to
Replication
• HIV attaches via
gp 120 to
T-cells that
posses surface
CD4 protein
molecules .
• A secondary
binding
protein(gp41) on
the virus locks to
a secondary
protein(CCR5)
on the cell
membrane.
1. HIV Attachment
Step 2: Infection
• HIV’s RNA,
enzymes, and proteins
are released into the
cell.
• The enzyme Reverse
Transcriptase
converts viral RNA
into proviral DNA.
• This process is called
reverse transcription
Step 3: Sabotage
• Integration:newly
made HIV DNA
moves to the cells
nucleus where it is
“spliced” into the host
DNA.
• HIV integrase helps
this process occur.
• The cell now contains
“proviral” DNA.
Step 4:Transcription
• Copies of proviral
DNA are
complemented into
mRNA via
transcription using the
cells own enzymes.
• HIV mRNA moves to
the cytoplasm ready
for assembly
5. Lysing and budding
• HIV RNA, proteins and
enzymes gather inside cell
membrane
• Viral envelope proteins
aggregate w/in the cell
membrane
• The enzyme Protease
cleaves RNA,viral
proteins & enzymes into
infectious viral particles.
• New viral particles bud off
to infect new CD4 cells
Drugs disrupt HIV enzymes at different stages
of infection
Fusion inhibitors
• Fusion inhibitors prevent
HIV from fusing or
docking with the host cell.
They may bind to HIV’s
gp41 protein and prevent
the virus from docking
with a T-cells CCR5
receptors
• If HIV cannot get into the
host cell, it cannot
replicate and cause disease
Nucleoside analogues
• A class of drugs that
fight HIV by
interfering with the
virus's ability to
make the key
enzyme "reverse
transcriptase”
• AZT
Vaccines
Antibodies
• Proteins found on the
surface of blood cells
and used by the
immune system to
identify viruses and
bacteria
Antigens
• The molecule found
on the surface of
viruses and bacteria
that is recognized by
immune cell
antibodies (an immune
response)
Attenuated
vaccines
• A vaccine created by
reducing the virulence of a
pathogen but still keeping
it viable
• (or “live”)
• Made by passing a virus
through a foreign host- it
mutates, then introduced
back to the original host.
• Advantage- Complete
immune response
• Disadvantage- Secondary
mutation may cause
reversion to virulence
Shingles
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Group Herpesvirus
DNA core
Icosahedral Shape
Enveloped
HIV (AIDS)
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Group Retroviruses
RNA
Icosahedral
Enveloped
Rabies
• Group Rhabdoviruses
• RNA
• Helical Shaped
• Enveloped
Polio
• Group Picornaviruses
• RNA
• Icosahedral Shaped
• Non-enveloped
Vaccines
• First Vaccine developed by Edward Jenner in
1776
• Observed that milkmaids did not acquire small
pox but did get a milder form that cows had
(cowpox)
• Took scabs from victims and inoculated it in his
son and others, then injected them with virus
Attenuated viruses
• Viruses are irradiated and
placed in a vaccine
• Their DNA is irradiated
and destroyed.
• Surface proteins are left
intact and gives the
immune system a chance
to recognize, and respond
with antibodies
Viroids
• Smallest known
particles to be able to
replicate
• Composed only of a
short strand of RNA
• Cause some plant
diseases
Prions
• Composed entirely of
amino acids (no
nucleic acid)
• Bad proteins-proteins
clump together inside
cells that lead to cell
death
Prions
• Mad Cow
• Scrapie
• Human form is CJD
(Creutzfeld Jakob
Disease)
• Turns brain to “mush”