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

2 Characteristics of Viruses Must reproduce(replicate) inside a host - The cell in which the virus replicates is called the host cell 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

3 Why are viruses considered non-living? Viruses don’t exhibit all the criteria for life: - they don’t grow or develop - they do not respire - they require a host for reproduction

4 Virus Structure

5 Bacteriophage Bacteriophages are viruses that infect bacteria - they are responsible for transduction in bacteria The virus has an inner core of nucleic acid and an outer coat made of proteins

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

7 Lytic Cycle

8 Steps of Infection in the Lytic Cycle 1. Attachment 2. Entry/Infection 3. Replication 4. Assembly 5. Lysis (cell ruptures) and releases new viruses

9 Small Pox- Lytic Jenner developed first vaccine 1798

10 Lysogenic Cycle

11 Herpes Simplex 1/Lysogenic

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

13 Lytic and Lysogenic Cycles

14 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

15 Retroviruses

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