Viruses What is the structure and function of viruses? How Germs Spread

What is a virus? Tiny, nonliving particles Need a host cell to reproduce Named based on disease or tissue – NO Latin names Ex. bacteriophage, rabies virus, adenovirus

Viral Structure Core - nucleic acid DNA/RNA Protein coat - capsid Some larger viruses have an outer viral envelope

Capsid Nucleic acid Envelope

Viral Shapes Importance - recognize specific host cell Cell-type specific or species specific Ex: polio virus – human nerve cells Ebola virus

Common virus shapes Polyhedral Cylindrical Spherical Polyhedral w/a tail

Attachment and Entry

Lytic Cycle Attachment Entry Replication Assembly Lysis and Release Ex. flu or Influenza

Bacteriophage Bacterial DNA Nucleic acid Bacterial host cell B. Entry The bacteriophage injects its nucleic acid into the bacterial cell. A. Attachment C. Replication D. Assembly E. Lysis and Release The host’s metabolic machinery makes viral nucleic acid and proteins. New virus particles are assembled. The host cell breaks open and releases new virus particles.

Lytic Cycle Animation

Lysogenic Cycle Attachment & Entry Provirus forms Cell Division Provirus leaves host DNA – why? Lytic cycle

Lysogenic Cycle Animation

Lytic and Lysogenic cycles

B. Provirus Formation A. Attachment and Entry C. Cell Division LYSOGENIC CYCLE LYTIC CYCLE The provirus leaves the chromosome. Viral nucleic acid and proteins are made. The cell breaks open releasing viruses. A lysogenic virus injects its nucleic acid into a bacterium. Bacterial host chromosome A. Attachment and Entry B. Provirus Formation Provirus The viral nucleic acid is called a provirus when it becomes part of the host’s chromosome. C. Cell Division Although the provirus is inactive, it replicates along with the host cell’s chromosome.

HIV virus  AIDS Lysogenic cycle Retrovirus – RNADNA HIV bud off w/out killing white blood cells

Other Viral Diseases Common Colds & Influenza Smallpox Human papillomavirus  warts Herpes simplex  Cold sores fever blisters

Defenses & Treatments Phagocytes white blood cells Antibodies Vaccine –before exposure Antibiotics do NOT work Treat symptoms Wash hands – remember the video clip