Presentation on theme: "Chapter 18 Viruses and Bacteria. Viruses, bacteria, viroids, and prions can all cause infection or disease Eukaryotic cells 10,000-100,000 nm Prokaryotic."— Presentation transcript:
Viruses, bacteria, viroids, and prions can all cause infection or disease Eukaryotic cells 10,000-100,000 nm Prokaryotic cells 200-10,000 nm Virus 50-200 nm Viroid 5-150 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 http://my.hrw.com/content/hmof/science/hig h_school_sci/tx/gr9- 12/hmd_bio_9780544073890_/dlo/biologyvid eoclips/index.html?vid=72
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 http://my.hrw.com/content/hmof/science/hig h_school_sci/tx/gr9- 12/hmd_bio_9780544073890_/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 http://my.hrw.com/content/hmof/science/hig h_school_sci/tx/gr9- 12/hmd_bio_9780544073890_/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
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