Viruses
Definition = Latin for POISON NON – Living because Do not grow Do not reproduce on their own Do not metabolize Living Because Evolve/Adapt Mutate and recombine
Discovery of the Virus Adolph Meyer (1833) a German Scientist studied the Tobacco Mosaic Virus. Thought it was caused by a very small bacterium because it could not be viewed through the microscope.
Infection by tobacco mosaic virus (TMV)
VIRUSES: GENES IN PACKAGES Viruses sit on the fence between life and nonlife VIRION = a virus particle Our body sees viruses as non living antigens and makes antibodies to fight them.
Viruses are parasites of cells. A virus takes over its cellular metabolism (think cellular factory) and makes hundreds, if not thousands of copies.
Viruses are specific for the kinds of cells they infect. For example: Influenza attacks only cells of the lungs. Hepatitis C attacks only liver cells. HIV attacks T4 white blood cells.
Examples of Different Types of Human Viruses Influenza (Flu)
HIV
Herpes Virus
Measles
Ebola Virus
Polio
2 MAIN PARTS OF A VIRUS: 1. Protein coat (capsid): Protects the nucleic acid core 2. Nucleic acid core – can be DNA or RNA An envelope is found in some viruses (usually those that infect animal cells). It is an additional protective coating.
Membranous envelope RNA Protein coat Protein spike
EXAMPLE OF A BACTERIOPHAGE (attacks bacteria) PROTEIN COAT (CAPSID) VIRAL DNA SHEATH TAIL FIBERS
Compare the size of a Eukaryotic cell, Bacterial Cell and a Virus
Viruses come in many shapes and sizes Measured in nanometers (nm) There are 109 nm in a meter (1 nm = 10-9 m) Cannot be seen with a light microscope
HOW ARE VIRUSES CLASSIFIED? TYPE OF NUCLEIC ACID (DNA or RNA) SHAPE B. HOST C. FUNCTION
Bacteriophages Bacteriophage is a virus that attacks bacteria Injects its DNA and takes over the bacteria cell. Phage: means to eat or destroy
0.5 m
Head Tail Tail fiber DNA of virus Bacterial cell
HOW DO VIRUSES MULTIPLY? Viruses perform replication in other cells called hosts. The two replication cycles that viruses go through are the LYTIC and the LYSOGENIC cycles.
The two cycles differ because in the lytic cycle a virus immediately replicates after entering the cell and in the lysogenic cycle the viral DNA replicates itself in a way that doesn’t kill the host cell immediately.
LYTIC CYCLE
LYSOGENIC CYCLE
TREATMENT OF VIRAL DISEASES Viral diseases cannot be cured by antibiotics. Generally with viral infections you are limited to relieving symptoms while your immune system battles the virus.
Prevention of Viral Infections – VACINES When you inject a person with a harmless (weakened or dead) form of a virus This stimulates the immune system to produce cells and proteins that will recognize and destroy that type of virus, if it enters the body again
This helped to end epidemics of smallpox, polio and measles
HUMAN USES FOR VIRUSES GENETIC ENGINEERING Viruses can help correct genetic defects by carrying desirable genes from one cell to another
AGRICULTURE Help control pests that destroy human food crops They eliminate harmful insects without creating pollution