Viruses, Bacteria and Germ Theory Unit 11

Germ Theory of Disease Throughout history, people have created many explanations for disease. Germ theory led to the understanding that many diseases are caused by microorganisms (viruses and bacteria). Experiments by Pasteur and Koch led to an understanding of the presence of microorganisms and their relationship to diseases

Invented Pasteurization – heat liquids to kill bacteria. Experiment disproved Spontaneous Generation (the idea that life can arise from nothing). Pasteur  Exposed pasteurized broths to air in swan-neck flask with a tube that wouldn’t allow dust particles to pass.  Nothing grew unless flasks were broken open.  Showed that microorganisms came from outside (spores on dust), not spontaneously generated in broth. Boiled Broth Remains Sterile Micro- organisms Grow

Koch Developed Koch’s Postulates – a test to see which microorganisms cause a specific disease The disease causing organism must be –  Found in all cases of disease  Removed and cultured (grown) in laboratory  Injected into a healthy organism to cause the same disease  Match the original sample when removed from organism #2 Diseased Animal Causes disease in healthy animal Same Pathogen Re-cultured Cultured Pathogen

Germ Theory of Disease Acceptance of the germ theory has led to modern health practices. – Aseptic (sterile) techniques to keep germs out of the body – Development of vaccinations and antibiotics to prevent and fight disease – Safe handling of food and water – Sanitation Death rate for mothers during childbirth  What happened in early 1900s?

Bacteria Unit 11

Bacteria Prokaryotic Cells (small, simple, no nucleus) Most abundant life forms on Earth. They can survive in many environments. Bacterial Cell Structures: – Cell wall – Cell membrane – Cytoplasm – DNA – Ribosomes – Pili (attach to other cells) – Flagella (movement)

Bacterial Shapes Rods: Bacillus Spheres: Coccus Spirals: Spirillum

Bacterial Diseases Plague, cholera, cavities, dysentery, typhoid fever, MRSA, acne Treatment: – Antibiotics – kill bacteria by affecting things that bacteria have but humans do not. – The first antibiotic discovered was penicillin in – Some bacteria have evolved to become resistant to antibiotics.

Examples of Good Bacteria Environment: Many bacteria act as decomposers to recycle nutrients to the soil Digestion: E. coli helps us digest our food Food/drink: Bacteria help with fermentation to make cheese, vinegar and alcohol Medical: Manufacturing insulin that is used to treat Diabetes

Viruses Unit 11

Viruses Viruses are NOT alive. – Not made of cells – Need a host to reproduce Basic Structure: – Nucleic Acid Core (DNA or RNA) – Protein Coat Very small – About 100X smaller than a bacteria – Can only be seen with electron microscopes

Viral Replication Some viruses insert genetic material into the host’s DNA, then remain dormant and reproduce later. (Chicken Pox  Shingles) 1. The virus attaches to a cell and injects DNA. 3. New viruses are made. 2. Viral DNA takes over protein synthesis. 4. The cell breaks open and releases viruses. Viruses need a host cell to transcribe and translate their genetic material. They cannot reproduce without a host.

Viral Diseases Common cold, the flu, rubella, mumps and measles, smallpox, hepatitis, polio, HIV/AIDS, and rabies Prevention: – Vaccines: Weak or inactive virus injected into body – This makes your immune system create antibodies so it can recognize and fight off the virus later Treatments: – Some anti-virals – NOT antibiotics! (which only work on bacterial infections)