Lecture VIII Protistans Dr. Kopeny Delivered 2/8, 2/11 Lecture VIII Protistans Lecture Themes structure and function; recurring evolutionary themes and unifying features the origin of mitochondria and chloroplasts Impact of Protists on Human Health and Welfare The key to understanding the protists is to recognize that a series of important innovations occurred, often repeatedly, as eukaryoites diversified. (Freeman 2002)
Source: Freeman (2002) surface waters teem with microscopic protists In some near-shore areas, gigantic protists from underwater forests Protists are particularly abundant in tidal habitats Morphologies and lifestyles found among protists. Protists are abundant in a wide variety of aquatic habitats. In marine environments, they are found in open ocean as well as in near-shore intertidal habitats (Freeman 2002) Euglena Eugleazoa includes both photosynthetic and heterotrophic flagellates. Most are autotrophic, but the lineage includes Trypanosoma
Ciliates dinoflagellates Alvoelata are unicellular, and bear a cavity called and alveoli. Diverse in body form. Apicompla water molds diatoms brown algae Stramenopilan are a diverse lineage of heterotrophs and phothynthetic forms (algae). The name refers to fine hairs on the flagella of members of this lineage
Rhodophyta are red algae unlike other eukaryotic algae, they lack flagella at any stage in their life history. They are the most abundant algae in tropical coastal areas Dulce, a large, edible red algae Volvox colonies Sea lettuce Green Algae and Plants evolved from a common photoautotrophic ancestor. Over 7000 species, mostly fresh water. Desmid
Choanoflagellida Flagellate protists. Possible ancestor to Sponges to Animals.
Size and Structure of Eukaryotic Cells compartmentalization and differentiation makes large size possible. Problem: transport and exchange limitations with increasing size Solution: compartmentalization Example: Paramecium Eukayotic compartments; nucleus, peroxisomes, mitochondria, chloroplasts, central vacuole, golgi, rough ER, smooth ER Paramecium, a predaceous protist that feeds on prokaryotes and other protists Nutritional and Metabolic Diversity in Protists Ingestive Lifestyles: Predation and Scavengers Absorbtive Lifestyles; Decomposers and Parasites Photosynthetic Lifestyles; Producers, many of which are symbionts Photosynthetic unicellular dinoflagellates Paramecium giant kelp Giardia, a unicellular human parasite
Predation and Scavenging Parasitism pseudopodia engulf food Ciliary currents sweepd food into gullet host parasite the parasite is a red algae with nonpigmented cells Symbiosis Photosynthetic pigments host symbionts Green cells are dinoflagellates inside a heliozoan Red: chlorophyll a and phycobilins Brown: chlorophyll a and chlorophyll c Green: chlorophyll a and chlorophyll b Many photosynthetic groups of algae are distinguished by the accessory pigments they contain, in addition to chlorophyll a. Each of these accessory pigments interecpts different wavelengths of light Consider the diversity of feeding modes in the lineage Alveolata Ciliates -many predators and herbivores -some parasite/basorbers (eg cattle guts, fish gills) -some feed via symbiotic photosynthesizers Dinoflagellates -half or so are photosynthetic, many others are parasitic Apicomplexans -most apicomplexans are parasitic Feeding diversity in protists, like electron donor and electron acceptor diversity in prokaryotes, no doubt drove phylogenetic diversification
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)
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
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
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.
Reproduction, Life Cycles and Alternation of Generations Meiosis and Sexual reproduction were important Protistan innovations
Life Cycle of Chlamydomonas http://megasun.bch.umontreal.ca/protists/chlamy/introduction.html http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html
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
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 www.bio.umass.edu/faculty/biog/margulis.html
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.
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. http://www.malaria.org/lifecycle.html 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
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