Viruses – Cellular Pirates

Adenovirus showing Varicella zoster virus icosahedral shape causes chickenpox

Chicken Pox – contains an envelope – membrane taken from the host – contains host glycoprotein trick the host cell into taking in the virus

Characteristics of VirusesObligate Intercellular Parasite

- Must reproduce(replicate) inside a hostStructure

- Nucleic Acid – DNA or RNA- Protein coat – called a capsid- Envelope – some contain a layer of membrane taken from a host cell

Mutate RapidlyHost Specific

- can only infect one type of cell

Small – from 20nm to 250nm - most are too small to be seen with a light

microscope

Virus Structure

BacteriophageBacteriophages are viruses that infect bacteria - they are responsible for transduction in

bacteria

Viruses have two life cyclesLytic Cycle-Viruses-immediately infect the

host cellLysogenic Cycle - lay dormant in the cell

Lytic Cycle

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. 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.

Lysogenic Cycle

Herpes Simplex 1/Lysogenic

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.

Lytic and Lysogenic Cycles

RetrovirusesContain 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

1. Virus attaches to the host2. Viral DNA is injected into the cell.3. New viruses are made4. Viruses are released

Identification of a new VirusTo identify a new virus, scientists would

look at the DNA sequence of this virus and compare it to others to see which it is most similar to.

The virus the new virus is most similar to is likely the one it mutated from.

Why are viruses considered non-living?Let’s first define life. Life = “an organismic

state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction.”

Viruses can’t do any of these things on their own. They must have a cell to metabolize nutrients, grow and reproduce.

Products like these help to keep your immune system healthy, but do not kill viruses themselves.

VocabularyObligate intercellular parasiteCapsidEnvelopebacteriophageLytic CycleLysogenic CyclePhageprophageRetrovirusReverse Transcriptase