Transcript Document

How are viruses transmitted?
What is a virus?
What are the characteristics of
living organisms?
What about viruses?
Viruses composed of nucleic acid
surrounded by capsid
• Nucleic acid can be DNA or RNA
– Can be single stranded or double
stranded
– RNA viruses have a higher rate of
mutation
Viruses composed of nucleic acid
surrounded by capsid
• Capsid = protein coat that surrounds the nucleic acid core
• The tiniest viruses are
20 nm in diameter.
(smaller than a
ribosome)
• Smallest viruses have
only 4 genes.
• Largest viruses have
several hundred.
• Capsid – a protein shell that covers the
viral genome. They may be
– Rod-shaped
– Polyhedral
– More complex
Capsids are built from large numbers of protein
subunits called CAPSOMERES
Anatomy of a Virus
• They consist of nucleic acids enclosed in a protein coat
and sometimes a membranous envelop.
Bacteria Viruses
• Bacteriophage = viruses that infect bacteria
• For research
T4 Phage
Plant Viruses
• Stunt plant growth
– This is a problem because use plants for food
Plant Viruses
• Enters through weakened or damaged plant
epidermis
• Spread from one cell to another cell through
the channels that connect adjacent cells
(plasmodesmata)
Animal Viruses
• Many have RNA nucleic
acid
– Common cold
– Measles
– Mumps
– Polio
– AIDS
• Some DNA animal viruses
– Hepatitis
– Chicken pox
– Herpes
Animal Viruses
• Nucleic acid core
• Outer envelope made
of phospholipids with
protein spikes
• Looks like a regular
cell membrane
The Influenza Virus
Herpes Virus
Ebola Virus
Viral Reproduction
A virus is not capable of reproducing on its own. It requires
A host cell for reproduction.
Lytic Cycle: Usually considered as the main method of
viral reproduction because it ends in the lysis of the
infected cell releasing the progeny viruses that will
in turn spread and infect other cells.
Lysogenic Cycle: Lysogeny in prokaryotes (bacteria cells)
is characterized by integration of the bacteriophage nucleic
acid into the host bacterium's genome.
Viruses can reproduce by the lytic
cycle
Bacteriophage - lytic cycle
Assembly & lysis (release)
Are released viruses
genetically the same as
the original virus?
Viruses can also reproduce by the
lysogenic cycle
lysogenic
ticking time
bomb
2 possible results ?
1)
after cell divisions,
lytic cycle kicks in or
2)
viruses escape via
budding, using host’s
cell membrane;
leaving host intact,
but weakened.
Envelope viruses (such as animal viruses) can
reproduce by budding
Methods of Transmission
Method of transmission depends upon the type of
virus.
•Direct contact skin-skin
•Air
•Body fluids
•Ingestion - food/water
Vaccination
Dead or weakened form of the virus builds immunity to specific
pathogens. Vaccines are a method of prevention. They do
not cure disease.
The benefit of a temperate virus
• A single infected cell can give rise to a
large population of cell carrying the virus in
prophage form
• This enables viruses to propagate without
killing the host.
What causes the switch?
• Usually an environmental trigger, such as
radiation or the presence of certain
chemical signals , that switches the virus
from the lysogenic to the lytic mode.
Viral Reproduction
• Can only reproduce within a host cell (obligate
intracellular parasite)
• They lack the enzymes for metabolism and
have no ribosomes or other equipment for
making their own proteins.
Are viruses alive?
•
•
•
•
•
•
Viruses do not
Grow
Metabolize
Viruses do
Infect and use the cell to make more viruses
Cause disease in many organisms
Government Agencies
• CDC- Center for Disease Control
• USMRIID- United State Medical Research
Institute of Infectious Disease
• BL1
• BL2
• BL3
• BL4
Outbreak Questions
1.
What are the 4 different BioHazard levels, describe each one.
2. Describe the 3 modes of transmission for Mutaba and which scenes depicted each.
3. Which structure of the virus mutated?
4. What was the consequence of the virus mutating?
5. What are biohazard levels? What level is Mutaba?
6. What is the function of the Center for Disease Control?
7. List 3 scientific realities concerning viruses in this movie.
8. Discuss 2 scientific non-realities concerning viruses in this movie.
9. Define the term host reservoir and explain why it was important to find the host reservoir for the Mutaba virus.
10. What are the differences between an antiserum and a vaccine.
11. Could an outbreak be a reality in the U.S.? Defend your position.
Thought question
12. Why are viruses specific to certain species?
13. How has commerce and global travel increased the spread of viruses?
14. Should the government force mandatory isolation of infected individuals?
15. Could viruses cause the extinction of humans?
16. Why are viruses good agents for bioterrorism?