PowerPoint Lecture Presentations prepared by Mindy Miller-Kittrell, North Carolina State University C H A P T E R 12 Characterizing and Classifying Eukaryotes Eukaryotic microorganisms Fungi Algae Water molds Slime molds Include both human pathogens and organisms vital for human life Reproduction of Eukaryotes More complicated than that in prokaryotes Eukaryotic DNA packaged as chromosomes in the nucleus Some produce asexual reproduction others reproduce sexually by forming gametes and zygotes Some both - Algae, fungi, and some protozoa reproduce both sexually and asexually 1
Reproduction in Eukaryotes Nuclear division Nucleus has one or two complete copies of genome Single copy (haploid) Most fungi, many algae, some protozoa Two copies (diploid) Remaining fungi, algae, and protozoa Two types Mitosis Meiosis Reproduction in Eukaryotes Nuclear division Mitosis Cell partitions replicated DNA equally between two nuclei Maintains ploidy of parent nucleus Four phases Prophase Metaphase Anaphase Telophase Mitosis Figure 12.1a Nuclear division: mitosis Diploid nucleus (2n) DNA replication 1 Prophase I Centromere Chromosome (two chromatids) 2 Metaphase Spindle 3 Anaphase 4 Telophase Nuclear envelope Two diploid nuclei (2n) 2
MEIOSIS II MEIOSIS I Reproduction in Eukaryotes Nuclear division Meiosis Nuclear division that partitions chromatids into four nuclei Diploid nuclei produce haploid daughter nuclei Two stages meiosis I and meiosis II Each stage has four phases Prophase Metaphase Anaphase Telophase Meiosis Figure 12.1a Nuclear division: Meiosis I Diploid nucleus (2n) DNA replication Tetrad (two homologous chromosomes, four chromatids) 1 Prophase I 2 Late prophase I Crossing over 3 Metaphase I 4 Anaphase I Chromosome (two chromatids) 5 Telophase I Figure 12.1a Nuclear division: Meiosis II Meiosis Chromosome (two chromatids) 5 Telophase I 6 Prophase II 7 Metaphase II 8 Anaphase II 9 Telophase II Nuclear envelope Four haploid nuclei (1n) 3
Diverse group defined by three characteristics Eukaryotic Unicellular Lack a cell wall Some are pathogens Nucleus Pseudopods Cilia Flagellum Motility by means of cilia, flagella, and/or pseudopods Figure 1.6 Locomotive structures of protozoa. 4
Distribution of Require moist environments Most live in ponds, streams, lakes, and oceans Critical members of plankton Animal cells without cell walls how do they survive in hypotonic solutions? Contractile vacuoles Closed vacuole Open vacuole Some have contractile vacuoles that pump water out of cells Morphology of Great morphological diversity Some have two nuclei Macronucleus Contains many copies of the genome Micronucleus 5
Many protozoans have different stages in life cycle Motile feeding stage called a trophozoite Resting stage called a cyst trophozoite cyst Reproduction of Most only reproduce asexually Binary fission or schizogony Few also have sexual reproduction Some become gametocytes that fuse to form diploid zygotes Some utilize a process called conjugation Figure 12.3 Schizogony. Merozoites Nucleus Schizont Multiple mitoses Cytokinesis 6
Figure 12.6 Sexual reproduction via conjugation in ciliates. Diploid micronuclei Compatible mates 1 Mates couple. 2 Meiosis of micronuclei produces four haploid micronuclei in each. 3 Three micronuclei in each disintegrate; the remaining two replicate by mitosis. Haploid micronuclei 4 Mates each swap one micronucleus. Haploid micronucleus (1n) Macronucleus (50n) Diploid micronucleus (2n) 5 Partners separate. 9 Three cytokineses 8 Original macronucleus partition a macronucleus disintegrates. Four 7 Three mitoses and a micronucleus into micronuclei become without each of four daughter cells. macronuclei by replicating cytokinesis chromosomes numerous produce eight times; four micronuclei micronuclei. remain micronuclei. 6 The two different micronuclei fuse to form diploid micronucleus. Nutrition of Most are chemoheterotrophic Obtain nutrients by phagocytizing bacteria, decaying organic matter, other protozoa, or the tissues of host Dinoflagellates and euglenoids are photoautotrophic Classification of based on 18s rrna sequences One current scheme groups protozoa into six groups Euglenozoa Parabasala Diplomonadida Alveolates Amoebozoa Rhizaria 7
Classification of Euglenozoa Euglenids Photoautotrophic, unicellular microbes with chloroplasts Historically classified as plants Figure 12.7 Trichonympha acuta, a parabasalid with prodigious flagella. Parabasala contain Golgi body like structure called a parabasal body Most of these organisms form a symbiotic relationship in animals; these include a variety of forms found in the intestines of termites and cockroaches, many of which have symbiotic bacteria that help them digest cellulose in woody plants. Hydrogenosomes reduced mitochondria Alveolates Ciliates Use cilia to move themselves or water All are chemoheterotrophs and have two nuclei Balantidium is the only ciliate pathogenic to humans Figure 12.10 A predatory ciliate, Didinium (on left), devouring another ciliate, Paramecium. 8
Alveolates Apicomplexans Chemoheterotrophic pathogens of animals Complex of organelles allow them to penetrate host cells Plasmodium, Cryptosporidium, and Toxoplasma cause disease in humans Alveolates Motile dinoflagellates have two flagella Dinoflagellates Unicellular microbes with photosynthetic pigments Historically classified as algae Large proportion of freshwater and marine plankton Many dinoflagellates are bioluminescent red tides Some produce neurotoxins 9
Classification of Amoebozoa Amoebae with lobe-shaped pseudopods and no shells Includes some human pathogens Entamoeba causing amoebic dysentry Slime molds are now classified as amoebozoa Two types Plasmodial slime molds Cellular slime molds Figure 12.14 Life cycles of slime molds. Haploid Myxamoebae germinate from spores. Compatible myxamoebae fuse. Spore (n) Zygote (2n) Plasmodium Haploid spores are released. Sporangium Coenocytic plasmodium (2n) Sporangia grow from plasmodial masses. Diploid Haploid Spores are released. Nucleus Sporangium Spore Myxamoeba germinates from spore. Fruiting body with sporangium Slug Slug forms stalk. Myxamoebae congregate to form pseudoplasmodium (slug), but they retain their individuality. Classification of Rhizaria Amoebae are protozoa that move and feed with pseudopods Rhizaria are amoebae with threadlike pseudopods Foraminifera Often live attached to the ocean floor Most are fossil species Radiolaria Have ornate shells of silica Live as part of the marine plankton 10
Figure 12.12 Rhizaria called foraminifera have multichambered, snail-like shells of calcium carbonate. Figure 12.13 Rhizaria called radiolarians have ornate shells of silica. 11