VIRUSES Viruses are non-living organisms. Technically they are not considered living organisms, since they cannot self replicate (they’re not a kingdom) Remember that living organisms: 1.Are highly organized 2.Stable chemical composition 3.Take energy & use it 4.Respond to stimuli 5.Grow & develop 6.Able to self reproduce (sexually or asexually) 7.Show genetic variation 8.Adapt to their environments
Virus structure Viruses: Just a protein coat for protection (capsid) and a nucleic acid (RNA or DNA) for information on how to make more copies of the same virus Cannot replicate/reproduce on its own! Needs a host…
Virus is a cellular parasite Uses cell machinery of a host cell to replicate and to produce more viruses They come in many varieties, sizes & shapes
Viruses cause diseases Viruses cause numerous diseases in Plants, animals, bacteria & fungi… Examples of human viruses: Herpes virus Hepatitis virus Rabies Ebola – emerging epidemics Influenza (“flu”) – respiratory infection (fever, headache, chills, cough, stuffy nose, sore throat) caused by a variety of viruses. Flu season: Nov. – March. Passed on by sneezing, coughing – air, hand-to-mouth, etc. Vaccine helps prevent outbreaks.
Human Viruses Human Immunodeficiency Virus (HIV) – causes AIDS. Transmitted through sexual contact, sharing infected needles, blood transfusions, mother to baby. Severe Acute Respiratory Syndrome (SARS) – brand new deadly virus, started in China, causes atypical pneumonia. Spreads quickly.
Plant Viruses Tobacco Mosaic Virus (TMV) causes mottling symptoms Rose mosaic virus Spots on fruit Wheat stunt virus
Kingdoms We learned last week that living organisms are divided into kingdoms… Kingdom Division Class Order Family Genus Species Taxonomic hierarchy for classifying organisms Scientific name = Genus + Species
Five Kingdoms Living organisms are classified in five kingdoms: Monera: bacteria, originally classified as plants because they have cell walls Protista: algae, slime molds, protozoa (have a cell wall, not cellulose) Fungi: mold, mildew, mushrooms. In past were class. as plants because they have cell walls and are ‘rooted’ in ground Plantae: Complex multicellular eukaryotes, obtain nutrients by photosynthesis Animalia: Complex multicellular eukaryotes, obtain food by ingestion
Living organisms PROKARYOTIC – Lack membrane-bound organelles –Kingdom Monera EUKARYOTIC – have membrane bound organelles. –Kingdoms Protista, Plantae, Fungi, Animalia
PROKARYOTES Bacteria are small and unicellular They have no internal organelles (no chloroplasts, nucleus, ER, mitochondria) Haploid (n) only
Bacteria Replication is asexual – clonal, rapid simple division (no mitosis) Pseudo-sexual reproduction, has means for Genetic exchange Called conjugation
Bacteria Bacterial forms: cocci, bacilli, spirilli Some forms are photosynthetic: cyanobacteria
Bacterial pathogens Animal pathogens: Typhoid, tuberculosis Bubonic plague or “Black Death”, transmitted by fleas (caused 25 million deaths in Medieval Europe) Syphilis, gonorrea (venereal diseases) E. coli, Salmonella (food poisoning) 76 million illnesses worldwide
Bacterial control There are ways of controlling bacterial growth: Disinfectants Antibiotics Low temperatures High temperatures, Low oxygen
Beneficial Bacteria Nitrogen-fixation – convert atmospheric N into useful Nitrogen (N gas plants animals) Decomposition in the biosphere – get rid of dead organisms, nature’s recyclers Intestinal Bacteria – supply vitamins (K) Commercial use: yogurt, sour cream, fermentation Genetically-engineered bacteria produce insulin and other important chemicals. Can also help clean up oil spills: oil ‘eating’ bacteria!
Eukaryotes Four Kingdoms: Fungi, Protista, Plantae, Animalia Have organelles (nucleus, mitochondria, etc.) Arose from endosymbiosis Endosymbiont Theory
Looking at the differences between prokaryotes and eukaryotes… How did eukaryotic organisms evolve? How did chloroplasts and mitochondria evolve? Chloroplasts and mitochondria: Same size as bacteria Have their own DNA Divide similarly
Endosymbiont Theory ( p.26, box 2.2 ) Chloroplasts and Mitochondria are descendants of once free-living prokaryotes that were engulfed by larger cells… establishing a symbiotic (mutually beneficial) relationship.
Kingdom Fungi Characteristics of fungi: Eukaryotic Non-photosynthetic, must obtain nutrients by absorption (produce digestive enzymes) Have a cell wall! Fungi cell wall is made of chitin and/or cellulose Occur in haploid (n) and diploid (2n) stages Reproduce sexually and asexually
Fungal morphology Most fungi come in thread-like strands, called hyphae (collectively called mycelium) Other fungi are single-celled, called yeasts. Form spores that can spread by wind, air or soil (give us allergies!) Fungi are so successful because they can reproduce both sexually and asexually –Sexual spores – (by meiosis) mushroom is spore- producing structure, formed by many hyphae –Asexual spores (by mitosis)
Fungal structure and reproduction Club fungi (mushrooms): Genetically compatible fungi fuse, combining cytoplasm and nuclei Nuclei in the same cell do not fuse, producing a heterokaryotic (n+n) hyphae – which in turn forms the fruiting body (mushroom) Underneath the cap, in the gills, n+n cells are called basidia Nuclei combine, form a zygote which undergoes meiosis and produces haploid spores of diverse genotypes for dispersal. See animation
Fungal fruiting bodies Coalescence of many hyphae. Role of spore production. Mushrooms Have cap and stalk. Spores are produced in the gills, under the cap.
Significance of Fungi Many fungi are beneficial As decomposers: fungi obtain nutrition from organic matter, so they recycle nutrients
Mycorrhizae Mycorrhizae (“fungus roots”) -- certain fungi grow into roots of most plants to supply water, P and N. 90% of plants need mycorrhyzae to survive An example of coevolution: symbiotic relationship. Fungus gets sugars from plants, and fungus provides P and water to plant
Fungi act as antibiotics Penicillin is produced by species of the fungus Penicillium, which kills bacteria. Discovered by Alexander Fleming in 1928. Left some unwashed plates with bacteria, went on vacation, and saw that a mold was growing, inhibiting the growth of the bacterial colony (Nobel Prize 1945).
Pathogenic fungi Pathogenic fungi grow within a host, using the host as food for replication Human Diseases: Athlete’s foot Yeast infections Ring worm Candidiasis
Pathogenic fungi: Mycotoxins Mycotoxins are harmful, toxic chemicals produced by fungi and which accumulate in infected food Aflatoxins contaminate corn and peanuts. The Aspergillus fungi grows on corn/peanuts and makes one of the most potent carcinogens known (aflatoxins)
Pathogenic fungi: Mycotoxins Ergot of rye – a fungus that infects the flowers of the rye plant. Produces fungal structures on the seed head, which are harvested with the rye seed bread Eating the Ergot-infected rye produces poisoning bye the compounds produced by the fungus (Ergotism or St. Anthony’s Fire) Causes nervous spasms, convulsions, delirium, tingling, gangrene. (40K deaths in yr. 944)
Plant Diseases caused by fungi Fungus can infect plant also Examples of fungal plant pathogens: Lawn diseases Apple scab Fire blight
Fungal plant pathogens Epidemics: Dutch Elm disease Wiped out American elms in U.S.
Irish potato famine Irish Potato Famine (1845) 1 million deaths, massive migration Caused by potato blight fungus Phytophthora infestans
Commercial uses of fungi Yeast for fermentation. Yeast breaks down sugars to produce ethyl alcohol and CO 2 Brewing of alcoholic beverages: beer, wine – yeast turns sugars of grains, grapes into alcohol and carbon dioxide (bubbles)
Commercial uses of fungi Bread making – carbon dioxide bubbles help dough rise
Commercial uses of fungi Cheese production – blue cheeses such as Roquefort Stilton Camembert
Commercial uses of fungi Edible fungi are the sexual structures of fungi, the mycelium remains Mushrooms Morels Truffles
Edible fungi Corn smut – a parasite of corn, is actually eaten in Mexico, a delicacy (huitlacoche)
Other types of fungus Poisonous – some very dangerous intoxicants Hallucinogenic fungi