Germ Theory and Viruses

Where does life come from?

Biogenesis

• Life comes from pre existing cells

• Examples include: Cells come from other cells

Spontaneous Generation

• Life arising from non-living (abiotic) material

  Examples include : Toads and snakes coming from the dirt

How is disease caused?

Miasma Theory: (Past)

-The theory that disease was caused by inhaling “bad air”

-Foul smelling air or vapors

-Unsupported today

Germ Theory: (Present)

-The theory that disease is caused by pathogens

-A pathogen is anything that can make you sick:

-Examples:

Inherited: Passed from parents to offspring

Environment: Cigarette smoke or pollution

Biotic Agents: Bacteria, Fungi, Protista

Viruses: Will infect different cells

Robert Koch:

Described the steps of infectious disease

How to identify the cause of a disease

Koch’s Postulates:

Identify and isolate microbe

Grow in pure culture

Reproduce the disease by injecting into another host and observe

Re-isolate microbe and repeat

Louis Pasteur:

Helped disprove spontaneous generation with Pasteurization

By heating a liquid, any microbes like bacteria can be killed off

In his experiment, a liquid was heated in an S-shaped flask. If the top of the flask were removed, bacteria grew, but if it were kept on, no bacteria were found.

Edward Jenner:

Created the first vaccine

Used a strain of “Cowpox” to prevent the infection of “Smallpox”

How are diseases spread?

Person to Person ~ Physical Contact

Contaminated Food/Water ~ Under/Un cooked meat

Vectors ~ Animals

Fighting Diseases ~

Antibiotics ~ Kills Bacteria, Doesn’t work on viruses

Vaccines~ Alert the immune system to fight against infections

Viruses

Not considered “alive”

Contains DNA and RNA

No organelles

Cannot reproduce unless in a host cell

Submicroscopic Infectious which causes many diseases

Classification

Classified based on what they attack

Example: Bacteriophage

• A virus that only attacks bacteria

Viral Diseases

AIDS

Measles

Hepatitis

Chickenpox

Smallpox

Influenza including H1N1

The common cold (Rhinovirus)

West Nile

Polio

Herpes

Structure of a Virus

Center core of DNA or RNA

Surrounded by a capsid

Reproduction processes

Lytic Cycle

1. Virus injects DNA into host cell

2. Viral DNA destroys host cell DNA

3. Cell bursts making copies of the virus

4. Host cell is destroyed

   
   
   Lysogenic Cycle

   1. Virus injects DNA into the host cell

   2. Viral DNA merges with host cell DNA

   3. Every time the cell creates a copy of itself then it also replicates the virus

   4. Does not immediately destroy the host cell