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Transcript
CHAPTER 29 LECTURE SLIDES Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protists Chapter 29 Chapter 29 Eukaryotic Origins • Eukaryotic cells differ from prokaryotes – Presence of a cytoskeleton – Compartmentalization (nucleus and organelles) • Appearance of eukaryotes in microfossils occurred about 1.5 BYA 3 • The nucleus and endoplasmic reticulum arose from infoldings of prokaryotic cell membrane 4 • Many organelles evolved via endosymbiosis between an ancestral eukaryote and a bacterial cell – Mitochondria • Aerobic bacteria engulfed by larger bacteria 5 • Chloroplasts – Larger bacteria engulfed smaller photosynthetic bacteria – Chloroplasts come from single line of cyanobacteria – Hosts are not monophyletic • Brown algae engulfed red algae that already had chloroplasts – Secondary endosymbiosis 6 • Endosymbiosis supported by – DNA inside mitochondria and chloroplasts • DNA similar to bacteria DNA in size and character – Ribosomes inside mitochondria similar to bacterial ribosomes – Chloroplasts and mitochondria replicate by binary fission – not mitosis 7 Defining Protists • Most diverse of the four eukaryotic kingdoms • United on the basis that they are not fungi, plants, or animals • Vary considerably in every other aspect – Unicellular, colonial, and multicellular groups – Most are microscopic but some are huge – All symmetries – All types of nutrition 8 • Protista is not monophyletic – Paraphyletic – Does not represent any evolutionary relationships • Grouping 15 major protist phyla into 7 monophyletic groups – 60 lineages are still not placed 9 Working model for protists classification 10 11 • Cell surface – Plasma membrane – Extracellular material (ECM) in some • Diatoms – Silica shells • Cysts – Dormant cell with resistant outer covering – Used for disease transmission 12 • Locomotion – Flagella • One or more – Cilia • Shorter and more numerous than flagella – Pseudopodia (“false feet”) • Lobopods – large, blunt • Filopods – thin, branching • Axopods – thin, long 13 • Nutrition – Phototrophs – Heterotrophs • Phagotrophs – Ingest particulate food matter • Osmotrophs – Soluble food matter – Mixotrophs are both phototrophic and heterotrophic 14 • Asexual reproduction – Typical mode of reproduction – Some species have an unusual mitosis • Mitosis – equal size daughter cells • Budding – one daughter cell smaller • Schizogony – cell division preceded by several nuclear divisions; produces several individuals • Sexual reproduction – May be obligate, or only under stress – Meiosis is a major eukaryote innovation – Union of haploid gametes which are produced by meiosis – Advantage in allowing frequent genetic recombination 15 • Multicellularity – From single cells to colonies to true multicellularity – Arisen multiple times – Fosters specialization – Few innovations have had as great an influence on the history of life 16 Diplomonads • • • • • Unicellular Move with flagella 2 nuclei Giardia Degenerate mitochondria 17 Parabasalids • Live in termite guts – Host cellulose degrading bacteria • • • • Trichomonas vaginalis – STD Undulating membrane for locomotion Use flagella Lack mitochondria – derived trait 18 Euglenozoa • Among the earliest eukaryotes to possess mitochondria • 1/3rd have chloroplasts and are autotrophic – May become heterotrophic in the dark • Others lack chloroplasts and are heterotrophic • All have a flexible pellicle • No sexual reproduction 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Euglena – Two anterior (and unequal) flagella a. 6.5 µm © Andrew Syred/Photo Researchers, Inc. • Attached at reservoir – Contractile vacuoles – collect excess water – Stigma – movement towards light – Numerous small chloroplasts • From ingestion of green algae – Concept of a single Euglena genus is now being debated 20 21 • Kinetoplastids – 2nd major group in Euglenozoa – Unique, single mitochondrion • DNA maxicircles and minicircles – Trypanosomes cause human diseases • African sleeping sickness – tsetse fly • Leishmaniasis – sand fly • Chagas disease – skin contact with urine or blood of infected wild animal 22 • Difficult to control because organisms repeatedly change their protective coat – Release of sterilized flies – Traps scented like cows but treated with insecticides – Sequencing of genomes revealed core of common genes in all 3 – hope for single drug target 23 Alveolata • Flattened vesicles called alveoli • Dinoflagellates • Apicomplexans • Ciliates • Common lineage despite diverse modes of locomotion 24 Dinoflagellates • • • • Photosynthetic, unicellular with flagella Live in aquatic environments Some are luminescent Do not appear to be directly related to any other phylum • “Red tide” are “blooms” – fish, birds, and marine mammals may die from toxins • DNA not complexed with histones 25 Apicomplexans • Spore-forming animal parasites • Apical complex is a unique arrangement of organelles at one end of the cell – Enables the cell to invade its host • Plasmodium causes malaria – Complex life cycle – sexual, asexual, different hosts – Eradication focused on eliminating mosquito vector, drug development, vaccines • DDT-resistant mosquitoes 26 27 Other apicomplexans • Gregarines – Found in the intestines of arthropods, annelids, and mollusks • Toxoplasma gondii – Causes infections in humans with immunosuppression – Can cross placental barrier to harm fetus 28 Ciliates • 3rd group of apicomplexans • Feature large numbers of cilia arranged in longitudinal rows or spirals around the cell • Pellicle – tough but flexible outer covering • 2 types of nuclei – Micronucleus – without will reproduce asexually – Macronucleus – essential for function • Have two types of vacuoles – Food vacuoles – digestion of food – Contractile vacuoles – regulation of water balance 29 30 • Conjugation – Only different mating types can conjugate 31 Stramenopila • Brown algae, diatoms, and oomycetes • Very fine hairs on their flagella – A few species have lost their hairs during evolution 32 Brown algae • Conspicuous seaweeds of northern regions • Life cycle involves alternation of generations – Sporophyte – multicellular and diploid – Gametophyte – multicellular and haploid • Not plants 33 34 • Diatoms – Phylum Chrysophyta – Photosynthetic, unicellular organisms – Unique double shells made of silica – Some move using raphes • Two long grooves lined with vibrating fibrils 35 Oomycetes • • • • “Water molds” Either parasites or saprobes Were once considered fungi Motile zoospores with two unequal flagella – Produced asexually • Undergo sexual reproduction • Found in water or on land • Phytophthora infestans – Irish potato famine (1845–1847) – 400,000 people died 36 Rhodophyta • Red algae range from microscopic to very large • Lack flagella and centrioles • Have accessory photosynthetic pigments within phycobilisomes • Origin has been a source of controversy – Tentatively, treated as a sister clade of Chlorophyta (green algae) 37 38 Choanoflagellida • Most like common ancestor of all animals • Single emergent flagellum, surrounded by funnel-shaped contractile collar – Structure matched in sponges • Use collar to feed on bacteria • Have a surface tyrosine kinase receptor found in sponges 39 Protists Without a Clade • Amoebas are paraphyletic – Rhizopoda (True amoebas) • Move by means of cytoplasmic projections called pseudopods 40 – Actinopoda (Radiolarians) • Glassy exoskeletons made of silica • Needlelike pseudopods 41 • Foraminifera – Heterotrophic marine protists – Pore-studded shells called tests, through which thin podia emerge – Use podia for swimming and feeding – Complex life cycles with haploid and diploid generations – Limestones are rich in forams • White Cliffs of Dover 42 43 • Slime molds – Were once considered fungi – Include two lineages – Plasmodial slime molds • Huge, single-celled, multinucleate, oozing masses – Cellular slime molds • Single cells combine and differentiate, creating an early model of multicellularity 44 • Plasmodial slime molds – Stream along as a plasmodium • Nonwalled, multinucleate mass of cytoplasm • Form called feeding phase – Ingests bacteria and other organic material – When food or moisture is scarce, organism forms sporangia, where spores are produced 45 • Cellular slime molds – Important group for the study of cell differentiation because of their relatively simple developmental systems – Individual organisms behave as separate amoebas – Move through soil ingesting bacteria – When food is scarce, organisms aggregate to form a slug – Slug differentiates into a sorocarp 46 47
