Chapter 18 Viruses and Bacteria

Viruses, bacteria, viroids, and prions can all cause infection or disease Eukaryotic cells 10, ,000 nm Prokaryotic cells ,000 nm Virus nm Viroid nm Prion 2-10 nm Any disease causing agent is called a pathogen

A virus is made of DNA or RNA and a protein coat –non-living pathogen –Can infect many organisms

Types of Viruses 1.A viroid is made of a single strand of RNA and causes disease in plants and is passed through seeds or pollen

2.A prion is made of only proteins it causes a misfolding of proteins and diseases in the brain.

Structure of a Virus 1.Capsid- protein coat that surrounds genetic material 2.Nuclear Envelope –Made of lipids or proteins 3.Genetic Material –DNA –RNA DNA or

Structure of a virus video clip h_school_sci/tx/gr9- 12/hmd_bio_ _/dlo/biologyvid eoclips/index.html?vid=72

Shapes of Viruses 1.Enveloped  Influenza 2.Helical  Rabies 3.Polyhedral  Foot and Mouth capsid lipid envelope proteins nucleic acid capsid lipid envelope proteins nucleic acid

Viruses that infect bacteria Bacteriophages infect bacteria. capsid DNA tail sheath tail fiber colored SEM; magnifications: large photo 25,000; inset 38,000x

V- virus I- injection R- replicate A- assembly L- lyse Viruses cannot reproduce on their own so they are NOT considered alive

Viruses cause two type of infections A lytic infection causes the host cell to burst host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle.

A lysogenic infection does no immediate harm. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle.

Virus entering cell video h_school_sci/tx/gr9- 12/hmd_bio_ _/dlo/biologyvid eoclips/index.html?vid=71

Viruses cause many infectious diseases There are many examples of viral infections. –common cold –influenza

Retrovirus is a virus that contains RNA and makes a copy of DNA, can remain dormant for years ex) cold sores (herpes),and HIV HIV-infected white blood cell

How are vaccines made?? Vaccines are made from weakened pathogens. – A vaccine stimulates the body’s own immune response. –Vaccines prepare the immune system for a future attack Vaccines are the only way to control the spread of viral disease.

Prokaryotes can be grouped by their need for oxygen obligate anaerobes are poisoned by oxygen obligate aerobes need oxygen facultative aerobes can live with or without oxygen

Bacteria video clip h_school_sci/tx/gr9- 12/hmd_bio_ _/dlo/biologyvid eoclips/index.html?vid=73

Bacteria commonly come in three forms 1.rod-shaped, called bacilli 2. spiral, called spirilla or spirochetes Lactobacilli: rod-shaped Spirochaeta: spiral

3. spherical, called cocci Strepto Staphlo Bacteria and archaea have similar structures. –plasmid –flagellum –pili Enterococci: spherical

Bacterial Structure flagellum pili plasmid cell wall chromosome plasma membrane This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences.

Gram Staining helps indentify bacteria –gram-positive stains purple, more peptidoglycan –gram-negative stains pink, less peptidoglycan Gram-negative bacteria have a thin layer of peptidoglycan and stain red. Gram-positive bacteria have a thicker peptidoglycan layer and stain purple.

Bacteria strategies for survival Bacteria can produce an endospore in harsh conditions

Reproduction Binary fission: Bacteria reproduce asexually one process is conjugation it allows them to exchange genetic material through a bridge

Obtaining energy aerobic vs. anaerobic - 1. Autotrophs 1. photosynthesis- EX: Cyanobacteria (blue-green algae) 2. chemosynthesis (chemo autotrophs)- EX: Archaeabacteria

Disease causing bacteria Bacteria cause disease by invading tissues or making toxins. –A toxin is a poison released by an organism. –Ex) staph

1.Bubonic plague- 2. Tuberculosis – 3. Strep throat – 4. E. coli poisoning – 5. Cholera –

Treatment of Bacterial Diseases Antibiotics: chemicals that kill the growth of bacteria do NOT work on viruses Some antibiotics are produced naturally by bacteria and fungi (molds) Penicillium mold

Antibiotic Resistance Bacteria are gaining resistance to antibiotics –overuse –underuse –misuse Antibiotics must be used properly.

Resistant Bacteria h_school_sci/tx/gr9- 12/hmd_bio_ _/dlo/biologyvid eoclips/index.html?vid=76

Important uses of Bacteria 1.Prokaryotes live in digestive systems of animals. –make vitamins –break down food 2. Bacteria help ferment many foods. –yogurt, cheese –pickles, sauerkraut –soy sauce, vinegar

3. Bacteria have many functions in ecosystems. –photosynthesize –recycle carbon, nitrogen, hydrogen, sulfur 4. Bioremediation uses bacteria to break down pollutants. -oil spills - biogradedable materials

Helpful Bacteria h_school_sci/tx/gr9- 12/hmd_bio_ _/dlo/biologyvid eoclips/index.html?vid=74