Virus!Not Alive,

But Still Deadly…

Bacteriophages or Virus?

Bacteriophages or Virus?• Bacteriophages attack bacteria

(prokaryotes)

• viruses attack eukaryotic cells.

• Viruses and bacteriophages invade cells and use the host cell's machinery to synthesize more of their own macromolecules.

Virus Versus CellLife Characteristic

Virus Cell

Growth No YesHomeostasis No YesMetabolism No YesMutation Yes YesNucleic acid DNA or RNA DNAReproduction Only within host

cellIndependently by cell division

Structure Nucleic acid core, protein covering, some have envelope

Cytoplasm, cell membrane, etc..

Viral Size and Structure

Viral Size and Structure• Virus shape is determined by the

genome and protein coat covering its genome

• Basic structure:– Capsid: Protein coat– Nucleic acid core: RNA or DNA

• Genome can be single or double stranded• Helps determine shape of virus

– Lipoprotein coat• Envelopes capsid in some viruses

Virus CategoriesViral Group Nucleic

AcidShape and Structure

Example

Papovaviruses

DNA Icosahedral, non-env.

Warts, cancer

Adenoviruses DNA Icosahedral, non-env.

Resp. & intestinal infections

Herpesviruses

DNA Icosahedral, enveloped

Herpes simplex, chicken pox, mono, shingles

Poxviruses DNA Complex brick, enveloped

Small pox, cow pox

Picornaviruses

RNA Icosahedral, non-env.

Polio, hepatitis, cancer

Myxoviruses RNA Helical, enveloped Influenza A, B, CRhabdoviruses

RNA Helical, enveloped Rabies

Retroviruses RNA Icosahedral, enveloped

AIDS, cancer

Virus Categories• DNA viruses – stable, do not mutate

rapidly– Single-stranded or double-stranded– Includes Smallpox and Hepatitis B

• RNA viruses – mutate rapidly, unstable– Single-stranded or double-stranded– Includes HIV and Rhinovirus

Lytic and Lysogenic Cycles

The Lytic Cycle• Virus attaches to host cell’s

membrane and injects its nucleic acid into the host cell.

• The viral nucleic acid takes over protein synthesis, creating new viruses.

• The host cell bursts, lyses, releasing the newly formed viruses.

The Lysogenic Cycle• Nucleic acid of virus becomes

part of the host cell’s chromosome

• Nucleic acid remains in the cell in this form for many generations

AIDS

HIV and AIDS• HIV is a retrovirus that leads to AIDS• The virus kills or damages cells of the body's

immune system, progressively destroying the body's ability to fight infections

• 25 million people worldwide have died from AIDS

• A combination of at least three drugs is recommended to suppress the virus from replicating and boost the immune system

• There is no cure for HIV and AIDS

Chickenpox

Chickenpox• Caused by the varicella-zoster virus (VZV)

and common in children under 12 • Highly contagious, itch rash• Children can be vaccinated against the

disease– Some children may still get chickenpox

though– Those that have had chickenpox have a

natural immunity to the disease• VZV can lie dormant within the body and

cause shingles later in life

Influenza

Influenza• Two common types: Influenza A and Influenza B• Flu Symptoms include:

– fever (usually high), headache, extreme tiredness, dry cough, sore throat, runny/stuffy nose, muscle aches

– Nausea, vomiting, and diarrhea can occur but are more common in children

• 5% to 20% of U.S. residents will get influenza each year– 36000 people on average die from influenza-related

causes– 200,000+ will admitted to the hospital as a result of

influenza-related causes.

Smallpox and Vaccination

Smallpox and Vaccination• Edward Jenner is credited with the first

vaccination against smallpox• Country-lore suggested that people who caught

cowpox from their cows did not get smallpox– Jenner transferred material from the pocks of a

dairymaid to James Phipps, the 8 year old son of his gardener

– James became mildly ill from cowpow• Weeks later, Jenner infected James with

smallpox– No infection now or during future trials

• The first vaccination published was a success!