Viruses – Cellular Pirates Enteric Adenovirus is an Icosahedral virus - common shape Chicken Pox – contains an envelope – membrane taken from the host – contains host glycoprotein trick the host cell into taking in the virus Adenovirus showing Varicella zoster virus icosahedral shape causes chickenpox 1

Characteristics of Viruses Obligate Intercellular Parasite - Must reproduce(replicate) inside a host Structure - Nucleic Acid – DNA or RNA - Protein coat – called a capsid Envelope – some contain a layer of membrane taken from a host cell Mutate Rapidly Host Specific - can only infect one type of cell Small – from 20nm to 250nm - most are too small to be seen with a light microscope 2

Virus Structure Helical virus – hollow tube of protein, icosahedron, phage 3

Bacteriophage Bacteriophages are viruses that infect bacteria - they are responsible for transduction in bacteria 4

Viruses have two life cycles Lytic Cycle-Viruses-immediately infect the host cell Lysogenic Cycle - lay dormant in the cell 5

Lytic Cycle 6

Small Pox- Lytic Jenner developed first vaccine 1798 Small pox virus can only live in humans. Spread person to person generally through close contact with infected person. Symptoms appear 12 –14 days after exposure. 1st symptoms are fever, tiredness, severe back pain, stomach pain and vomiting. This last 2-3 days and at this time the person is highly contagious to others.Then over the next 5 days the bumps appear. Today we have a vaccine for small pox. We have 15.5 million doses available now. A contract has been made to produce 210 million does this year!! Today the risk of the disease is less than the risk from the vaccine so people do not get vaccinated. Vaccine can be helpful if you are exposed up to 4 days after exposure. 7

Lysogenic Cycle 8

Herpes Simplex 1/Lysogenic 9

Shingles-Lysogenic/ Chicken pox virus (herpes varicella-zoster) Shingles is caused by the chicken pox virus. It can develop in anyone who has had chicken pox. The chicken pox virus remains dormant or inactive (lysogenic cycle) in nerve root cells of the body. Shingles is the second outbreak of the chicken pox virus. Usually happens in older people (65) because of weakened immune system.Typical case of shingles lasts about a month. If you get it on your face you should see a physician because it can led to blindness. 10

Lytic and Lysogenic Cycles 11

Retroviruses Contain RNA and not DNA - to be able to take over a host cell, the retrovirus must be able to convert the RNA into DNA - to accomplish the conversion, retroviruses insert an enzyme called Reverse Transcriptase into the host cell

Retroviruses

Vocabulary Obligate intercellular parasite Capsid Envelope bacteriophage Lytic Cycle Lysogenic Cycle Phage prophage Retrovirus Reverse Transcriptase 14