Viruses

1. Viruses Chapter 18.1

2. What is a virus? • A virus is nucleic acid wrapped in a protein coat • Can be DNA or RNA • Viruses are considering nonliving because they can’t reproduce on their own • The cell that a virus uses to reproduce is called a host cell • Viruses are named after the disease they cause or the organ they affect • Viruses that affect bacteria are bacteriophages

3. Viral Structure • The inner core is made of DNA or RNA • The outer coat of protein is called a capsid • If a virus has another layer of protection this is called the envelope • Viruses can be composed to 4 genes or 100’s of genes • 4 shapes • Polyhedral • Spherical • Helical • Phage

4. Attachment to host cell • Viruses must attach to the host cell to enter • Viruses attach using receptor sites • Once a virus attaches it injects it’s DNA or RNA into the host cells • Viruses tend to be species specific

5. Viral Replication • Lytic cycle • Virus attaches • Virus injects nucleic acid into host cell • Host cell replicated viral DNA • Virus particles are assembled • The host cell breaks open (dies) and releases new virus particles • Lysogenic cycle • Virus attaches • Virus injects nucleic acid into host cell • Viral nucleic acid is incorporated into host cell genome, called a provirus • Host cell divides, replicating genome with viral provirus, creating new cells that have the viral DNA • Proviruses can be dormant for many years. When triggered, they enter the lytic cycle

6. Retroviruses • Retroviruses use a more complex reproduction cycle • Use reverse transcriptase to make DNA from an RNA template Cancer and viruses • Several cancers are causes by viruses • HPV • Prions are proteins with no nucleic acid that are folded incorrectly • Can cause mad cow disease • Viroids are just a single strand of RNA with no protein coat