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

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. Viral Reproduction Lysogenic Cycle: Lysogeny in prokaryotes (bacteria cells) is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome. A virus is not capable of reproducing on its own. It requires A host cell for reproduction.

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 DiseaseUSMRIID 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?