Viruses – Cellular Pirates Adenovirus showing Varicella zoster virus icosahedral shape causes chickenpox

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

Virus Structure

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

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

Lytic Cycle

Small Pox- Lytic Jenner developed first vaccine 1798

Lysogenic Cycle

Herpes Simplex 1/Lysogenic

Shingles-Lysogenic/ Chicken pox virus (herpes varicella-zoster)

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