Lecture #10 2/11 Dr. Kopeny

Transcription

1 Lecture #10 2/11 Dr. Kopeny Locomotion and Structures for Support and Protection Modes of Locomotion in Protists Pseudopodia An Amoeboid Protist flagella cilia Structure of microtubules in cilia and flagella A ciliatedprotist 2 single microtubules (red) surrounded by nine paired microtubules (yellow)

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3 A ciliated protist reference: chapter 4 in textbook Paramecium can swim in either direction relative to its long axis by beating its cilia in rhythmic, coordinated fashion that progresses from one end of the cell to the other. Amoeba extends a pseudopodium toward a Pandorina colony. At right, the amoeba surrounds colony before engulfing it

4 Source: Hickman et al 2001 Proposed mechanism of psuedopodial movement. In endoplasm, actin subunits are bound to regulatory proteins that keep them from assembling. External Structures for Support and Protection Sources: Purves et al (2002), Freeman (2002) Forams; shells are made from protein hardened with calcium carbonate Radiolarians; glassy skeletons allow light penetration for photosynthetic endosymbionts Amoeba; shell made of cemented sand grains foraminiferan with calcium carbonate tests diatomshave glasslike silicon containg sructures Diatoms Dinoflaggelates surrounded by cellulose plates

5 Multicellularity Source: Freeman 2002 True multicellarity is defined functionally Differentiation of cell function (specialization, division of labor) Differential gene expression Multicellularity has evolved independently multiple times in Protistan lineages Multicelluarity confers advantages by allowing for increased size, specialization, and complexity The initial evolution towards multicellularity begins with differentiation of gamete-producing cells, the consequence of the uniquely eukaryotic reduction division process; meiosis Multicellular Green Alga (Coleochaete orbiculairs) Clamydomonas Gonum Pandorina Volvox Morphological continuum in Volvocales from unicellular to multicelluar.

6 Reproduction, Life Cycles and Alternation of Generations Meiosis and Sexual reproduction were important Protistan innovations

7 Life Cycle of Chlamydomonas

8 Sporophytes (2n) Gametophytes (n) Life cycle of Laminaryia: an example of alternation of generations Sporophytes of this seasweed are usually found in water just below the line of the lowest tides, attached to the rocks by branching holdfasts In early spring, at end of the main growing season, cells on the surface of the blade develop into sporangia sporangia produce zoosporres by meiosis Zoospores are all structurally alike, but about half of them are capable of developing into a male gametophyte and half into a femlel gametophye. Gametophytes look nothing like the sporophytes, being short, branched filaments that grow on the surface of subtidal rocks Male gametohytes release sperm, and female gametophytes produce eggs, which remain attached tot eh gametophyte. Eggs secrete a chemical signal that attracts sperm of the same species, thereby increasing the probability of gametic union in the ocean. Sperm fertilize the eggs The zygotes grow into new sprorophytes, starting life attached to the remains of the old female gametophyte

9 Lines of evidence indicating mitochondria and chloroplasts arose as prokaryotic symbionts -membranous enzymes and transport systems -replication process -genome -protein translation machinery, including ribosomes, t-rna -similarities of mitochondrial and chloroplast ribosomes to prokaryote ribosomes Endosymbiotic Theory Lynn Margulis U. Mass., Distinguished Professor and Member of the National Academy of Science developed endosymbiotic theory 2.5 um 80 um Proteobacteria Cyanobacteria Margulis webpage

10 Phylogenetic analyses using small subunit RNA Ribosomes are comprised of one small and one large subunit. The single rrna molecule of the small subunit Ribosomes are Gene for small subunit r-rna is present in all organism good gene for determining deep branching in tree of life Sequence comparisons show that closest prokaryote relatieves of mitochondria are altpha proteobacteria. Sequence comparisons of plastids from various photosynthetic eukaryotes cluster with prokaryotic cyanobacteria (photosyntheitc machinery and metabolic pathways are shared as well.

11 Protists and Human Health: Plasmodium and Malaria P. falciparum is the most widespread and dangerous of the four: untreated it can lead to fatal cerebral malaria. The distribution of malaria varies greatly from country to country and within the countries themselves. In 1990, 75% of all recorded cases outside of Africa were concentrated in nine countries Infected Red Blood Cells Infected mosquito bites and infects person; sporozoites and enter liver cells After several days, undergo multiple divisions to become merozoites (specialized spore) that uses apical complex to penetrate RBC Merozite Apex Red blood cell 0.5 um Merozoites reproduce asexually in RBC s and lyse cells at 48 or 72 hr intervals (species specific); coordinated lysing of cells causes periodic chills and fever. Some merozoite infect new RBC s, some divide to form gametocytes; gametocytes that infect a biting female mosquite compete the life cycle in her body. Gametocytes form gametes and fertilization occurs in mosquito digestive tract; zygote is the only dipolid stage in the life cycle Oocyst develops in wall of mosquito gut. Thousands of sporozoites develop in the oocyst and then migrate to mosquites salivary gland

12 Source: Freeman 2002 HUMAN IMMUNE-DEFENSE AGAINST PLASMODIUM Plasmodium Infection Interpretation Strain Rate cp26 cp29 cp26 and cp29 strains together cp27 cp28 Low Low High High Average HLA-B53 binds to these proteins. Immune resonse is effective Immune response fails when these strains infect the same person HLA-B53 does not bind to these proteins. Immune response is not as effective Co-evolutonary Arm Race Strong association between HLA-B53 allele and protection against malaria found in West Africa HLA-B53 in infected liver cells bind to particular sporozoite protein and display protein-protein complex before they produce merozoites Recognition breaks down in people coinfected by certain strains NS leads to iimmune system adaptations for protection and to pathogen adaptations to overcome them Evolution of Land Plants Prior to the origin and diversitication of green plants in the mid-silurian (~450 mya), multicellular life was virtually entirely apapted to, and confined to, aquatic lifestyles Contintnenal Land Masses virtually unoccupied by multicellular organism multicellular-based ecosystems constituted tremendous potential for adaptive radiation Terrestrial life in a gaseous medium required evolutionary solutions to structural, physiological and ecological challenges; Many of these innovations can be regarded as exaptations of pre-existing traits of green algae from which green plants diverged Artist s rendering of Carboniferous forest in a tropical river delta. Most of the plants depicted here were nonseed tracheophytes 10 to 20 meters tall. In the distance, earl seed plants up to 40 meters tall towered over the forest.

13 Green algae of phylum Chlorophyta, such as Chara sp., are most likely ancestors of plants. Copyright BPS. Kingdom Plantae is monophyletic assemblage, descended from Green algae Chlorophyll a and b are homogous in Chlorophyta, Charaphyta and Plantae Currently includes over 250,000 described species classified in 12 monophyletic phyla Most are terrestrial, some are secondarily aquatic Diversification in plants involved successive adaptive radiations following evolution of key innovations that increased efficiency in an gaseous (air) and solid (Earth) environment Major problems were posed by gravity and by water loss/availability -maintain body structure resist gravity -obtain, transport and retain water -fertilize eggs and produce and protect embryos Major evolutionary innovations included -dimorphic body -waxy cuticle and stomata -vascular tissue; -jacketed sex organs; antheridia and - archegonia -life history dominated by sporophyte generation -seeds embryo with nutritive tissue in protective covering -flowers; vehicles for pollination strategies