Transcript Virus Structure & Functionnew

Virusus
Non-living
infectious agents
Require host (parasites)
Found everywhere.
Infect organisms in every
kingdom
Edward Jenner-first vaccine
for smallpox 1796
Viral Diseases
Viral
diseases:
– Smallpox, Polio, Measles,
Influenza, AIDS, Common
Cold
Viruses are Infectious Agents
But are Host Specific
and tissue specific
For Example:
Cold Virus only infects the cells of
the human upper respiratory tract.
Virus Structure
All
contain these 2 structures :
–1. Nucleic Acid (either RNA or
DNA)
–2. Protein Coat (capsid)Made of protein
Encloses Genetic material

Viral Body Plans
Complex virus
(bacteriophage)
Helical virus Poylhedral virus
Some
are Enveloped:
have an added
phospholipid membrane
on outside.
Examples:
HIV, Rhinoviruses ,
Coronovirus
Influenza
HIV is an Enveloped
Retrovirus
Has RNA
Retrovirus=RNA—to DNA---To
RNA---To protein
Mutates quickly.
HIV replication. 1.
HIV Replication
 1.
Binds to specific cell-Helper T cell (white
blood cell).
 2. Virus attaches, & viral RNA enters.
 3. Production -uses host materials to make DNA
 4. DNA enters nucleus; RNA made via
transcription.
 5. RNA leaves nucleus, translation occurs.
 6. Assembly of new viruses.
 7. Exits by budding and/or lysis of cell.
viral RNA
DNA
protein coat
protein
subunits
of coat
sheath
base plate
18 nm
diameter,
250 nm
length
tail fiber
viral coat
(proteins)
viral
RNA
80-nm diameter
65-nm diameter head,
225-nm total length
reverse transcriptase
100-120 nm
diameter
lipid envelope; proteins span
the envelope, line its inner
surface, spike out above it
Fig. 20.11, p. 317
Virus ReproductionTakes
~20 min to make hundredsto-thousands of new viruses
Various
methods--but 5 basic steps—as
follows:
 1.
Virus Reproduction-5 basic steps.
Lytic Cycle
Attach to host cell surface.
 2. Entry: whole virus OR just
DNA
 3.Replication-takes over & direct
replication of viral DNA &
Proteins
 4. Assembly-new viruses
 5. Release. By either Budding or
Lysis which results in cell death.
Defense Against Viruses
1. ??Antibiotics—INEFFECTIVE—
because they target cellular processes
(viruses are not alive—no cell/processes)
2. Vaccinations—Made of viruses which have
been treated so they are harmless
Create our own self-defense-build internal
antibodies against specific viruses.
2.
Defense Against Viruses
 3. Virus-Destroying
Drugs. They
destroy the virus BUT ALSO
DESTROY HOST CELL
– Example: AZT-slows down
AID’s; it’s toxic therefore side
effects
Why Don’t Vaccines Always
Protect?
Mutations –
Unrecognizable
ЖФξ
HIV, Cold Virus, Influenza change
often
Viral surface proteins mutate; some
VERY OFTEN
Of all the changeable viruses, HIV
changes the most!
Become
Emerging Viral Diseases
Filovirus: A virus harbored in animals
without harming them; then passed on to
another animal who is harmed
FOR EXAMPLE: Ebola :30-90%
mortality
hemorrhagic fever.
PrionDisease
Fig. 20.6, p. 314
Other Infectious Agent--Prions
Small abnormal forms of proteins necessary for
operation of neuronsproteins
Proteins coagulate as large deposits in brainLinked to human diseases
– Kuru
– Creutzfeldt-Jakob disease (CJD)
Animal diseases
– Scrapie in sheep
– Bovine spongiform encephalopathy(mad cow
disease)
PrionDisease
Fig. 20.6, p. 314