Download Viruses – Cellular Pirates

Viruses – Cellular Pirates
Adenovirus showing
icosahedral shape
Varicella zoster virus
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)
Lytic and Lysogenic Cycles
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