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Chapter 7. Taxonomy and Viruses taxonomy • an artificial* system of classifying organisms according the inferred (presumed) relationships among organisms. • the premise is that the more features two organisms have in common, the closer they are related. ***artificial because it is an invention of man. This implies that its validity is open to question. the purpose: • to assist in the identifying of organisms. • to provide a basis for recognizing natural groupings of living things. Binomial nomenclature - Carolus Linnaeus (1707-1778) • the scientific name given to organisms made up of it’s genus (pl.genera) and species name. Commonly the names are Latin or Greek which in themselves provide some description of the organism…if you understand Greek and Latin that is! e.g. Castor canadiensis - beaver Acer rubrum - red maple (What do you suppose ‘canadiensis’ refers to?… …how about ‘rubrum’) 1 Genus Species Common name Ursa americanus American black bear Ursa horribilis Grizzly Ursa arctos Alaskan brown bear Ursa maritimus Polar bear Ailuropoda melanoleuca Panda Phasocolarctos cinereus Koala From the table, what would you assume about the relationships between these ‘bears’? dichotomous key - a series of two answer questions, which when followed to completion serves to determine the identity of an organism. The process is commonly referred to as ‘keying out’ an organism. (…So if you want to impress someone, you say,”Sorry I can’t go to the movies tonight. I have to spend some quality time in the lab and ‘key out’ some insects.” Usually, they become awestruck and ask if they can come too…either that or tell you that you need to get a life.) e.g. Insect key in Peterson’s Field Guide Levels of Classification 2 Taxa Kingdom dandelion Plantae housefly Animalia human Animalia Phylum Tracheophyta Arthropoda Chordata Class Angiospermae Insecta Mammalia Order Asterates Diptera Primates Family Compositae Muscidae Hominidae Genus Taraxacum Musca Homo Species officinale domestica sapiens The Five Kingdom System of Classification All living organisms can be catagorized into one of five different kingdoms. Monera - single celled prokaryotes (anything lacking nuclei). E.g. Bacteria and cyanobacteria (blue-green algae) Protista - single (and some multi-) celled eukaryotes (have nuclei) E.g. Protozoa and simple algae. Fungi - multicellular (usually) heterotrophs (get nourishment from some other source). E.g. Mushrooms, molds, yeast Plantae - multicellular autotrophs (photosynthetic) E.g. Seaweeds, mosses, ferns, conifers, flowering plants Animalia - multicellular heterotrophs E.g. You, me, kitty, puppy, and goldy (you know…the fish) The Phylogenic Tree 3 A schematic diagram representing inferred relationships between organisms…assumes macro-evolution from common ancestor. Figure 7.4 4 Viruses biological particle incapable of reproduction on its own. Once inside a living cell it reproduces. Non-living yet reproduces (maybe best thought of as somewhere between living and non-living.) Extremely small - 20 to 400 nm. Extremely simple ‘anatomy’; only a small piece of single or double stranded DNA or RNA (but not both) in a protein capsid. Capsid amounts to ~95% of the virus and gives the virus it’s particular shape. Tobacco mozaic virus Adenovirus Bacteriophage. Sometimes has an outer lipid membrane believed to be ‘inherited’ from the host cell membrane. Not all viruses are disease causing. Viruses can be quite specific (selective) to the types of cells that they infect. Some infect only plant, only animal or only bacteria. Wide ranges: swine flu virus hogs and humans rabies virus rodents,dogs, humans and others Narrow ranges: 5 human cold virus cells of upper respiratory tract AIDS virus certain types of white blood cells Some bacteriophages infect only bacteria in a very narrow range. This appears to indicate that the bacteria might be related. Viral Replication There are two strategies by which viruses replicate: ◊ Lytic - a very quick replication whereby the nucleic acid (DNA or RNA) is injected into the host cell; the host cell replication machinery is hijacked and multiple copies of virusees are produced within about 25 - 45 minutes. Host cell bursts (lysis) spreading new viruses everywhere. This is considered a virulent reproduction. ◊ Lysogenic - a very slow replication where the virus DNA/RNA is inserted into host DNA and replicated as part of the normal host life cycle. The virus remains dormant until some signal causes it to enter the lytic cycle. Lysogenic is considered a temperate reproduction. ***prophage - the term given to the viral DNA/RNA when it is in dormant stage. Figure 7.7 6 Immune Defence System The human immune system can be divided into two main components: non-specific defences - these are general means which resist all types of pathogens. (a.k.a. ‘baddies’) included are: skin - physical barrier oil/sweat glands - acidic barrier which kills many pathogens ciliated mucous membranes - physical sweepers of airborne pathogens gastric fluid - acid/chemical barrier against food-borne pathogens natural bacteria flora - act as surface competition for foreign bacteria macrophages - act like Pac-man in the blood to gobble up foreign bodies complement system - 20 plasma proteins which act like tag-alongs on foreign bodies so macrophages can find them faster. Specific Defences a very complex system in which the presence of a pathogen causes antibody production, which aids in the response. The problem is that it takes some time for this production to occur. Once it does though, the body can deal with the invader. The cool thing is that some of the antibodies are then stored in the lymphatic system so if that SAME pathogen infects a second time, the immune response will be fast, fast, fast! Look out pathogen, ‘cuz it will be Bam! Kapow! Viral Diseases 7 A few definitions: ◊ endemic - when the pathogen is with us all the time (common cold) ◊ epidemic - when disease spreads rapidly (some of the annual influenza outbreaks) ◊ pandemic- when the disease spreads so rapidly that it becomes a global problem (AIDS) ◊ oncogenic viruses - cancer caused by viruses inserting specific genes into a cell. ◊ interferons - a chemical produced by the body which INTERFERES with the viruses’ ability to infect other cells. ◊ viroids - free RNA…wipe out seed potatoes ◊ prions - protein coats with no nucleic acid…slow fatal CNS disease in humans Some other examples: ◊ polio(myelitis) ◊ small pox ◊ measles Phylogeny - in other words: if your an evolutionist, Where did they come from. Nobody knows, but there are a few ideas. Viruses: • were once unicellular parasites, but didn’t need there organelles, so they lost them. (even evolutionists have problems with this one) • were once ‘free-living pre-cells(?) that later became parasites of cellular organisms. (this one too) 8 • were fragments of DNA from some ancestral cell. (most figure this would be more likely) What is Gene Therapy? Read p.205 vector - in biology it is some sort of carrier. For example, mosquitoes are vectors for malaria. Virus Viral DNA removed Target DNA inserted Patient's immune deficient Reinjected white blood cells into patient Target DNA is replicated as cell divides & becomes part Immune defifiency is overridden of patients DNA Review Questions p 205 Chapter Review 9