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Lecture VIII Protistans. 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.
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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 Trypanosoma Eugleazoa includes both photosynthetic and heterotrophic flagellates. Most are autotrophic, but the lineage includes
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.
Lecture Themes structure and function; ecurring 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)
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 Giardia, a unicellular human parasite giant kelp
Parasitism Predation and Scavenging 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 Brown: chlorophyll a and chlorophyll c Red: chlorophyll a and phycobilins 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
Modes of Locomotion in Protists Pseudopodia An Amoeboid Protist flagella cilia Structure of microtubules in cilia and flagella 2 single microtubules (red) surrounded by nine paired microtubules (yellow) A ciliatedProtist
Interrelated cytoskeletal functions -maintain cell shape -provide for cell movement -serve as tracks for motor proteins
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 Actin subunits in endoplasm are bound to regulatory proteins to prevent assembly On stimulation, hydrostatic force carries subunits to hyaline cap where lipids in membrane free actin subunits from regulatory proteins subunits quickly assemble into filament sand on intearction with actin-binding protein, form gel-like ectoplasm calcium ions at trailing edge activate actin-severing proteins, loosening network enough to that myosin molecules can pull on it Proposed mechanism of psuedopodial movement
Sources: Purves et al (2002), Freeman (2002) External Structures for Support and Protection Radiolarians; glassy skeletons allow light penetration for photosynthetic endosymbionts Amoeba; shell made of cemented sand grains diatoms have glass-like silicon containg sructures Dinoflagelates surrounded by cellulose plates White Cliffs of Dover are limestone composed almost entirely of protistan fossil shells, including forams and coccolithophores (an alga) foraminiferan with protein-hardened, calcium carbonate tests Diatoms
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 The three basic eukaryotic life cycles are shown here – all occur among Protists, and other variations on these as well Life cycle of a diploid species in which the multicellular organism is diploid Life cycle of a diploid species in which there is an alternation of generations of multicelluar form – 1n gametophye and 2n sporophyte Life cycle of a diploid species in which the multicellular organism is haploid
http://megasun.bch.umontreal.ca/protists/chlamy/introduction.htmlhttp://megasun.bch.umontreal.ca/protists/chlamy/introduction.html http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html
Stages of Sexual and Asexual Lifc Cycles Mature cell is haplid Mature cell reproduces asexaully; is resorbs its flagella and then divides twice by mitosis Daughter cells devlop flagella and cell walls, then emrge as swimming zoospores from wall of parcnt cell. Zoospores grow to mature haploic cells, completing asexual lfie cycle. Sexual reproduction is triggered by shrotage of nturients,dryong of the pond, or some other stress. Within the wall of the parent cell, mitosis produces many haploid gametes. After their release, gametes from opposiste mating types (desginated + and -) pair off and cling together. Fusion (syngamy) of the gametes froms a diploid zygote. Zygote secrests a durable coat that protects cell against harsh conditions When zygote breaks from dormancy, meiosisi produces four haploid individuals (two of each mating type that emerge from the coat and grow into mature cells. Life Cycle of Chlamydomonas Inset shows mature cells before reproduction
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 Sporophytes (2n) Gametophytes (n) Life cycle of Laminaryia: an example of alternation of generations
Endosymbiotic Theory 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 Lynn Margulis U. Mass., Distinguished Professor and Member of the National Academy of Science – developed endosymbiotic theory 2.5 um 80 um Margulis webpage www.bio.umass.edu/faculty/biog/margulis.html Proteobacteria Cyanobacteria
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. 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 http://www.malaria.org/lifecycle.html 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 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 co-infected by certain strains NS leads to iimmune system adaptations for protection – and to pathogen adaptations to overcome them Plasmodium Infection InterpretationStrain Rate cp26 Low cp29 Low HLA-B53 binds to these proteins. Immune resonse is effective Immune response fails when these strains infect the same person cp26 and cp29 strains together High cp27 Highcp28 Average HLA-B53 does not bind to these proteins. Immune response is not as effective
Chlamydomonas Genome Project and the Origins of Green Plants http://megasun.bch.umontreal.ca/protists/chlamy/introduction.html http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html Postulated phylogenetic position of Chlamydomonas, inferred from molecular and morphological data. Branch lengths are arbitrary and do not reflect phylogenetic distance. Postulated global eukaryote phylogeny based on presence or (ancestral) absence of mitochondria, and shape of mitochondrial cristae. Chlamydomonas belongs to the flattened clade.
Encysted zoospores land on a substrate and germinate, growing into the tufted byody of hypae Several days later, organism begins to form sexual structures meosito produces eggs in oogonia on separate brances fo the same or different idndividuals, meiosis produces several haploid sperm nuclie contained within compartments called antheridial hyphae hypae grow like hooks around the oogonium and depsoit their nuclei through fertiliaation tubes that lead to eggs. The resulting zygotres )oospores) may degvelop resistant walls but are also protected within the walls of the old oogonia dormant perido followd, duuring which oogonium wall usually disintegrates Zygotes germinate and form short hyphae tipped by zoosporangia, and the cycle is completed Ends of hyphae form tubular zoosporangia Each zoosporangium produces about 30 biflaagellated zoosppres asexually Life Cycle of a cellular slime mold (Dictyostelium)
