Viruses, Bacteria and Germ Theory Unit 11 Viruses, Bacteria and Germ Theory

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

Boiled Broth Remains Sterile Pasteur Invented Pasteurization – heat liquids to kill bacteria. Experiment showed that life cannot arise from nothing (disproving Spontaneous Generation) Boiled Broth Remains Sterile 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. Curved Neck Removed Micro-organisms Grow

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

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?

Unit 11 Viruses

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

Viral Replication 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. Some viruses insert genetic material into the host’s DNA, then remain dormant and reproduce later. (Chicken Pox  Shingles)

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 if you are exposed to a full version later Treatments: Some anti-virals NOT antibiotics! (which only work on bacterial infections)

Unit 11 Bacteria

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 Bacillus Rods Coccus Spheres Spirullum Spirals

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 called penicillin in 1929. 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

How Bacteria Obtain Energy Two major categories: Autotrophs - Make their own energy - 2 types Phototrophic autotrophs - Get energy from sunlight Chemotrophic autotrophs - Get energy from inorganic molecules (eg. Sulfides) 2. Heterotrophs - Energy obtained from other organisms Chemotrophic heterotrophs - obtain energy by dissolving/absorbing organic material Phototrophic heterotrophs - meet some energy needs from photosynthesis, but must absorb organic compounds.

Bacterial Reproduction Bacteria reproduce through binary fission. Can engage in primitive sexual reproduction called conjugation. A bridge is formed between 2 bacteria (pili) Plasmids are shared across bridge, thus exchanging genetic information. In times of harsh conditions, bacteria can form endospores, to encapsulate themselves in a dormant state, until conditions improve.