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Viruses, Bacteria, Protists, & Fungi Phylogeny •Cladistics is a way to analyze primitive and derived characters and by the construction of phylogenetic trees called a cladogram Arrange taxa into a cladogram based on shared derived characters. •A cladogram is a special type of phylogenetic tree A clade is an evolutionary branch that includes: •A common ancestor, together with •All its descendent species It traces the evolutionary history of the group being studied • Tracing Phylogeny • Fossil Traits • Fossil record is incomplete • It is often difficult to determine the phylogeny of a fossil • Homology • Refers to features that stem from a common ancestor • Homologous structures are related to each other through common descent • Analogy • Similarity due to convergent evolution • Analogous structures have the same function in different groups but do not have a common ancestry • Structures look similar due to adaptation to similar environments Viruses • Debate about whether they are “alive”…most scientists do not consider them to be alive….that is why they do not belong to a kingdom • Associated with a number of plant, animal, and human diseases • Can only reproduce using the metabolic machinery of the host cell • noncellular • May have a DNA or RNA genome. • Invention of the electron microscope allowed these infectious agents to be seen for the first time Viral Structure • 10 - 400 nm in diameter(really small!!!) • Each type has at least two parts • Capsid: Outer layer composed of protein subunits • Some are enveloped by membrane • Others “naked” • Nucleic acid core: DNA or RNA • Vary in shape Replication of Viruses •Gain entry into specific host cell •Capsid (or spikes of the envelope) adhere to specific receptor sites on the host cell surface. •Viral nucleic acid then enters a cell •Relies on host cell enzymes, ribosomes, transfer RNA (tRNA), and ATP for its own replication •Bacteriophages – Viruses that infect bacterial cells Bacteriophage • There are two types of bacteriophage life cycles The lytic cycle • Viral reproduction occurs • The host cell undergoes lysis(rupture) The lysogenic cycle • Viral reproduction does not occur immediately but may occur in the future • Becomes integrated into the host genome • Becomes latent • May later reenter the lytic cycle Special cases • Viroids • Naked strands of RNA • Many crop diseases • Prions • Protein molecules with contagious tertiary structure • Some human and other animal diseases - Mad cow disease( Krutzfeld-Jakob) Prokaryotes • Include domains Bacteria and Archaea, which are fully functioning cells • Microscopic • Range in size from 1-10 µm in length and 0.7-1.5 µm in width • Abundant in air, water, and soil and on most objects • Louis Pasteur showed that a previously sterilized broth cannot become cloudy with growth unless it is exposed directly to the air Prokaryote Structure • Lack a membrane-bounded nucleus (DNA in nucleoid region) • Outer cell wall • Some move by means of flagella • Lack membranous organelles • May have accessory rings of DNA (plasmids) Reproduction in Prokaryotes • Asexual • Prokaryotes reproduce asexually by means of binary fission • Mutations are generated rapidly and passed on to offspring quickly • Some bacteria form resistant endospores under unfavorable conditions Genetic recombination in prokaryotes: • Conjugation • Conjugation pilus forms between two cells • Donor cell passes DNA to recipient cell through the pilus Domain-Bacteria/Kingdom Eubacteria • Over 9,000 different bacteria have been named. • Most bacterial cells are protected by a cell wall • Contains peptidoglycan • Bacteria are commonly differentiated using the Gram stain procedure • Bacteria can be further classified in terms of their three basic shapes • Spiral (spirilli), • Rod (bacilli), and • Round (cocci) Cyanobacteria •Formerly called the Blue-Green algae (Cyanophyta) •Cyanobacteria are Gram-negative bacteria that are photosynthetic •Believed to be responsible for introducing oxygen into the primitive atmosphere •Lack visible means of locomotion •Can live in extreme environments •When commensalistic with fungi, form lichens Domain Archae-Kingdom Archaebacteria •Archaea were earlier considered Bacteria •Other differences: •Archaea do not have peptidoglycan in their cell walls like the Bacteria •Archaea are biochemically more like Eukarya than Bacteria •Archaea are now thought to be more closely related to Eukarya than to Bacteria Archae • Many live in harsh conditions: • Anaerobic marshes • Methanogens • Produce methane from hydrogen gas and carbon dioxide • Salty lakes • Halophiles • Require high salt concentrations for growth • Hot sulfur springs • Thermoacidophiles • Reduce sulfides and survive best at temperatures above 80ºC • Plasma membranes contain unusual lipids that confer tolerance of high temperatures Domain Eukarya •Protist: single cell, eukaryotic, some autotrophic and some heterotrophic •Fungi: multi-cellular, eukaryotic, cell walls with chitin, heterotrophic •Plantae: multi-cellular, eukaryotic, cell walls with cellulose, autotrophic •Animalia: multi-cellular, eukaryotic, no cell walls, heterotrophic Protista •Classified in the domain Eukarya and the kingdom Protista. •The endosymbiotic hypothesis •Aerobic bacteria became mitochondria •Cyanobacteria became chloroplasts •Vary in size from microscopic algae and protozoans to kelp more than 200 m in length •Although many protists are unicellular, they are highly complex. •Amoeboids and ciliates possess unique organelles, such as contractile vacuoles. •Some protists are colonial or filamentous • Nutrition: • Some are photosynthetic • Many are heterotrophic • Some ingest food by endocytosis • Some are parasitic • Some are mixotrophic • Combine autotrophic and heterotrophic nutritional modes • Life cycles: • Asexual reproduction is common • Sexual reproduction may occur when conditions deteriorate • Formation of spores allows protists to survive hostile environments. • A cyst is a dormant cell with a resistant outer covering • In parasites, a cyst may serve as a means of transfer to a new host •Protists are of enormous ecological importance •Photoautotrophic forms: •Produce oxygen •Function as producers in both freshwater and saltwater ecosystems •Major component of plankton •Organisms that are suspended in the water •Serve as food for heterotrophic protists and animals • Algae refers to many phyla of protists that carry out photosynthesis • green algae (approximately 17,000 species) • Inhabit a variety of environments including oceans, freshwater, snowbanks, tree bark, and turtles’ backs • Volvox (a colonial chlorophyte) • A colony is a loose association of independent cells • A Volvox colony: • A hollow sphere • Thousands of cells arranged in a single layer surrounding a watery interior Diatoms • are the most numerous unicellular algae in the oceans • Significant portion of plankton are diatoms • Ornate silica shell Dinoflagellates •About 4,000 species of unicellular aquatic and marine organisms •Typically have two flagella •Symbiotic dinoflagellates called zooxanthellae are found in corals •Dinoflagellates provide their host with organic nutrients •Corals provide wastes that fertilize the algae •Some lack chloroplasts and are parasitic Ciliates • Hundreds of cilia beat in coordinated rhythm • Most swallow food whole • Divide by transverse binary fission during asexual reproduction • Two nuclei of differing types • Micronucleus – Reproduction • Macronucleus – Metabolism • Sexual reproduction involves conjugation and exchange of haploid nuclei Euglenids •Small freshwater unicellular organisms •Difficult to classify •Animal and plant-like •Have two flagella and an eyespot (shades a photoreceptor) •Cell is bounded by flexible pellicle •Chloroplasts/Eyespot Amoebozoans •Pseudopods form when cytoplasm streams forward in a particular direction •Amoeboids are protists that move and ingest their food with pseudopods(false foot) •Undergo phagocytosis for food Fungi • Saprotrophs - Cells release digestive enzymes and then absorb resultant nutrient molecules •Animals and fungi are more closely related to each other than either is to plants. •A flagellated unicellular protist was most likely the common ancestor of fungi and animals •Fungal anatomy doesn’t lend itself to becoming fossilized •Probably evolved a lot earlier than the earliest known fungal fossil dated 450 MYA. Structure of Fungi •Body (thallus) of most fungi is multicellular mycelium (yeasts are unicellular) •Consists of a vast network of thread-like hyphae •Septate fungi have hyphae with cross walls •Hyphae grow at their tips •Give the mycelium a large surface area per unit volume •Cell walls of chitin, like insect exoskeletons •Excess food is stored as glycogen as in animals Reproduction of Fungi •Both sexual and asexual reproduction •During sexual reproduction, hyphae from two different mating types fuse •Hyphae that contain paired haploid nuclei are said to be dikaryotic •Nuclear fusion produces a diploid nucleus, which produces haploid spores by meiosis •Spores germinate directly into haploid hyphae without embryological development Life cycle of Sac fungi •Asexual reproduction is the norm •Yeast usually reproduce by budding •A small bulge forms on side of cell •Receives a nucleus and gets pinched off and becomes full size •The other ascomycetes produce spores •Ascus refers to the fingerlike sac that develops during sexual reproduction •Ascus may be surrounded and protected by sterile hyphae within a fruiting body called an ascocarp •Haploid hyphae fuse to make a diploid nucleus •Meiosis followed by mitosis produces 8 ascospores Yeasts Yeasts can be both beneficial and harmful to humans. Only single cell fungus • Saccharomyces cerevisiae are used to make beer and wine • Candida albicans is a yeast that causes fungal infections. •Oral thrush is a Candida infection of the mouth, common in newborns and AIDS patients. Molds •Can be helpful to humans. • Aspergillus is a group of green molds used to produce soy sauce by fermentation of soybeans. • Aspergillus is used to produce citric and gallic acids •Can be harmful to humans • Trichophyton causes athletes foot (a type of tineas) same fungus causes jock itch & ringworm • Histoplasma capsulatum leads to the “fungal flu” and causes systemic illness Symbiotic Relationships of Fungi •Lichens •Symbiotic association between a fungus and a cyanobacterium or green alga •Specialized fungal hyphae penetrate the photosynthetic symbiont •Nutrients are transferred directly to the fungus •Possibly mutualistic, but the fungal symbiont is probably a parasite of photosynthetic symbiont •Can live in areas of extreme conditions(bare rock/wood) •Contribute to soil formation •Sensitive indicators of air pollution Mycorrhizae •Mutualistic relationships between soil fungi and the roots of most plants •Give plant greater absorptive surface •Help plants acquire mineral nutrients in poor soil