The Nature of Viruses

Chapter 27

Structure of Viruses

Types of Viruses

• DNA• RNA• Retroviruses

Main Shapes

• Helical

• Icosahedral

Sizes of Viruses

How Viruses Replicate

• 1. Attach to and Enter Host Cell• 2. Take over Protein synthesis machinery

inside of cell- Lysogenic Cycle• 3. Lytic Cycle- Lyse out of cell to go make more

Virus Babies

Retroviruses

• Use Reverse Transcriptase to make Viral RNA into DNA – HIV is a Retrovirus

Who can get a virus?

• Just about every kind of organism• Obligate intracellular parasites• Host Range and Tissue Tropism– Hep- liver– Rabies-neurons– Chickenpox…..can you ever really get rid of it?

HIV

• AIDS first reported in the US in 1981• Originated in Africa in the 1950’s based on the

rate of mutation• Closely related to a chimpanzee virus

Some people are resistant to HIVHow?

• Recent research suggests that people who were immuned to smallpox may also be immuned to AIDS

• Due to a mutation in CCR5 receptor• Makes virus unable to bind to cells and enter.

How the HIV Infection Works

Treatments

• Combination Drug Therapy– AZT and Protease inhibitors

• Vaccine Therapy• Chemokines and CAF• Blocking CCR5

Other Viruses

• Flu– Recombination vs mutation

• Emerging viruses– Ebola– Sars– Hantavirus

• Viruses can cause cancer

Prions and Viroids

• Prions- misfolded protein • TSE’s are caused by prions– Why is this controvericial?

• Viroids- infections RNA with no protein coat.