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The World of Microbes: Viruses & Bacteria AP Biology Chapter 23 Microbes are… Viruses Bacteria Protists Microbiology is the study of microbes! Small is Relative! 1µm Staphylococcus Cyanobacterium Escheria coli Eukaryotic Cells (10-100 µm) Prokaryotic Cells (0.2-10 µm) Viruses (0.05-0.2 µm) Viruses Viruses Viruses • DNA or RNA surrounded by a protein coat • Parasitic - require a host cell (like cells of your body) to replicate • Infect all kinds of organisms: Bacteria Plant cells Animal cells • Some viruses only affect certain parts of their hosts ex. Rabies affects nervous system Are Viruses Alive? Viruses are not regarded as living organisms; lack some attributes of life. • Are infectious particles, incapable of replicating independently. • Lack cellular organization and metabolism. Viruses Replication • Viruses reproduce only inside living cells. • Viruses replicate by infecting susceptible cells and using the cell to make more viruses. Viruses Various illnesses: flu, AIDS, common cold Some antiviral medicines Evolve very, very, rapidly Makes effective treatment difficult Each virus has a host range A limited number of host cells that it can infect Virus Shape Viral shape is determined by the nature of the virus’s protein coat. Viruses such as the rabies and herpes viruses are surrounded by an extra envelope derived from membranes of the host cell. Viruses Come in Many Shapes Herpes Rabies Bacteriophage Measles Tobacco Mosaic Viruses infect bacteria Bacteriophages Viruses called bacteriophages • Can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli Bacteriophages Infect Bacteria Bacterium Newly forming bacteriophages In this electron micrograph, bacteriophages are seen attacking a bacterium. They have injected their genetic material inside, leaving their protein coats clinging to the bacterial cell wall. The black objects inside the bacterium are newly forming viruses. Viral Structure - HIV Envelope (lipid bilayer) Core Proteins Receptor Genetic Material 2 RNA molecules Reverse Protein Transcriptase Coat Cross section of the virus that causes AIDS Inside is genetic material surrounded by a protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template after the virus enters the host cell. HIV is among those that also have an outer envelope that is formed from the host cell’s plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the envelope and help the virus attach to its host cell. Herpes Virus Envelope (lipid bilayer) Herpes Viruses Viral DNA in protein coat Protein Coat How Viruses Replicate: Herpes 2a. Viral envelope merges with nuclear membrane 2b. Protein coat disintegrates; viral DNA copied & enters nucleus nucleus envelope coat DNA DNA mRNA (cytoplasm) 1. Virus enters cell by endocytosis 3. Viral DNA transcribed to mRNA, which moves to cytoplasm How Viruses Replicate: Herpes envelope coat 5. New viruses assembled & bud from nucleus, get envelope from inner nuclear membrane nucleus DNA DNA mRNA (cytoplasm) 4. MRNA makes proteins, which enter nucleus 6. Newly formed viruses leave the cell by exocytosis Herpes Virus Viruses such as the herpes virus can remain hidden in the cell for a long time without reproducing. • Ex. Herpes virus that causes cold sores No symptoms appear until something causes the virus to be active, • such as a fever or sunburn. As long as the virus does not reproduce, there are no symptoms. When the virus reproduces again, the cold sores reappear. Viruses Diseases caused by viruses are hard to treat or cure. There are no known drugs to destroy viruses, although some may be effective in temporarily treating them. The white blood cells of the Immune System may surround a destroy a virus. Antibodies may help destroy viruses. • Antibodies only act on one specific kind of virus. Viruses Vaccines • Harmless substances made from weakened or dead viruses • Stimulate the immune system to create defenses (antibodies) against the actual pathogen • Can prevent certain viral illnesses Examples: chicken pox, flu, measles, mumps, rubella, hepatitis Prokaryotes: Archaea & Bacteria The Tree of Life All living things classified in three domains: • Bacteria • Archaea • Eukarya Amazing Living Things Microbes indispensable to life: Produce much of Earth’s: Oxygen Decomposition Over half of Earth’s biomass More bacterial cells than human cells in your body! Prokaryotes Prokaryotes have: • Circular DNA, RNA, ribosomes, cytoplasm, plasma membrane • Most prokaryotes have a cell wall, a capsule (around the cell wall) and a flagellum Prokaryotes don’t have: • Organelles such as nucleus, chloroplasts, mitochondria. Generalized Prokaryote Nucleoid DNA Plasmid DNA Cytosol Flagellum Capsule Plasma Membrane Cell Wall Prokaryotic DNA The area that contains the genetic material is referred to as the nucleoid. The genes are usually in one continuous circular loop of DNA. There may be other small circles of DNA outside the nulceoid called plasmids. Bacteria/Archaea Habitats (name a place, and they live there!) • They are specialists human skin, mouth, respiratory tract, large intestine, urogenital tract, etc. salty Dead Sea extreme pH archea in deep sea vents: 90-106o C • Aerobes and anaerobes Some Prokaryotes Thrive in Extreme Conditions Cyanobacteria in Yellowstone Hot Springs Archaea Unique lipid membranes, cell walls, and rRNA Methanogens • Convert CO2 to methane • Swamps, hot springs, vent communities, cow stomachs Halophiles - survive concentrated salt environment Thermoacidophiles - thrive in hot, acidic environment Generally in EXTREME environments Bacteria Evolve Rapidly Most of the time are asexual Classified by shape, locomotion, pigments, nutrients, colonies Bacteria Shape: • Cocci - round • Bacilli - rod • Spirilla - spirals Three Common Bacterial Shapes (b) (a) (c) bacillus cocci spirillus The Prokaryote Flagellum Flagella Bacterium Bacteria Reproduction Reproduction is asexual, by simple splitting (binary fission) Daughter cells are genetic clones of the parent cell Binary Fission DNA Bacteria - Reproduction Binary fission: • Very fast, up to once every 20 minutes • One bacterium-> 1021 in 24 hours. Conjugation: (sexual reproduction) • Used only occasionally. Bacteria – Sexual Reproduction Conjugation: • Genetic variation through pili (structures similar to flagella) and plasmid DNA • DNA is exchanged between bacterial cells • Occurs through a special large, hollow pilus • One bacterium acts as a donor, transferring DNA to the recipient. Conjugation Donor Recipient Sex Pilus Benefits of Bacteria Symbiosis (mutualism) • Ruminants’ digestive tracts • Nitrogen fixing in soil, nodules on certain legumes • Bacteria on/in the human body: intestines and vitamin K and B12 Biodegradation - oil Food production - cheese, yogurt, sauerkraut Decomposers Our Relationship With Bacteria Bacterial Pathogens Some cause disease = pathogenic In humans: • Strep throat • Toxins - tetanus, botulism • Pneumonia • "Flesh-eating" bacteria • Plague • Tuberculosis • Cholera • Lyme disease ANTIBIOTICS= anti bacterial!!! The Causes of Tooth Decay Transmission of Bacterial Pathogens Airborne Water Food Direct (skin contact, blood, and other body fluids) Insect vectors and other hosts such as deer tick (Lyme) or mosquito. Germ Theory of Disease Theory that microorganisms are the cause of disease. 1859 – Louis Pasteur • Credited with the idea that human diseases were caused by bacteria and viruses (germ theory) • Very important discovery in the field of medicine • Also created vaccinations to prevent disease Infectious Diseases Average age of death, in first world countries, jumped 30+ years in last century due to antibiotics, and enhanced hygiene and nutrition. Antibiotic-resistant infections on the rise in hospitals in the U.S. • This is due to bacterial evolution in response to widespread use of antibiotics!