What is a virus? • Made of two parts • Capsid—Nucleic acid • Different shapes (477)
Viruses: composed of nucleic acids enclosed in a protein coat (Capsid)
Only infect certain things • Bacteriophage
Viral Replication CyclesLytic cycle • A virus invades a cell. Takes over the host cell’s genes to make new viruses. • This causes the cell to burst and more viruses are released.
Viruses that go through lytic cycle • Common cold • Flu • Measles • Chicken pox • Ebola • Smallpox • Polio
Lysogenic cycle • This is a replication cycle in which the DNA is integrated into the host cell’s chromosomes. Cells replicate with viral genes. • Each new cell has viral genes. • Virus can sit idle for many years before becoming active. Example: hepatitis, HIV
Viruses that go through the lysogenic cycle (Provirus) pg 481 • Chicken pox • Herpes • Hepatitis
Symptoms of Provirus • Herpes simplex 1 – Cold sore; virus continues to live in body on nerve. • Stress could cause the activation of lytic cycle • Cold sores are not genital herpes
Chicken pox Genital Herpes Cold sores are different strains
HIV / AIDS • Retrovirus—made of RNA (pg 481, Fig 18.5) • Infects white blood cells and destroys them • Lysogenic life cycle
Viruses are Specific • Viruses can usually attach to only a few kinds of cells. • Example: Polio viruses infect only intestinal and nerve cells.
Origin of Viruses • Cells came first • Nucleic acids broke from an original host • First virus identified: Tobacco Mosaic Virus This virus caused poor tobacco plant growth. Affected profit
Are Viruses Living? • Not made of cells • Can reproduce, but only inside a host • Adapt / evolve • Do not utilize energy
Wash hands (hand sanitizer if you can’t wash), cover mouth, don’t touch face (nose, eyes, mouth)