lecture viii – protistans – dr - university of...
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Lecture VIII – Protistans – Dr. Kopeny Delivered 2/8, 2/11
Lecture VIII Protistans
Lecture Themesstructure 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)
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)
Source: Freeman (2002)
Eugleazoa includes both photosynthetic and heterotrophic flagellates. Most are autotrophic, but the lineage includes
Trypanosoma
Euglena
Alvoelata are unicellular, and bear a cavity called and “alveoli”. Diverse in body form.
Apicompla
dinoflagellates
Ciliates
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
water molds
diatoms
brown algae
Rhodophyta are red algae – unlike other eukaryotic algae, they lack flagella at any stage in their life history. They arethe most abundant algae in tropical coastal areas
Dulce, a large, edible red algae
Green Algae and Plants evolved from a common photoautotrophic ancestor. Over 7000 species, mostly fresh water.
Volvox colonies
Sea lettuce
Desmid
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
Giardia, a unicellular human parasitegiant kelp
Paramecium
Predation and Scavenging Parasitism
pseudopodia engulf food Ciliary currents sweepd food into gullet
host parasite
the parasite is a red algae – with nonpigmented cells
host symbionts
Green cells are dinoflagellates inside a heliozoan
Red: chlorophyll aand phycobilins
Brown: chlorophyll aand chlorophyll c Green: chlorophyll
a and chlorophyll b
Photosynthetic pigmentsSymbiosis
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
Apicomplexans-most apicomplexans are parasitic
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
Feeding diversity in protists, like electron donor and electron acceptor diversity in prokaryotes, no doubt drove phylogeneticdiversification
Consider the diversity of feeding modes in the lineage Alveolata
Locomotion and Structures for Support and Protection
Pseudopodia
flagella
cilia
Structure of microtubules in cilia and flagella
Modes of Locomotion in Protists
2 single microtubules (red) surrounded by
nine paired microtubules (yellow)A ciliatedProtist
An Amoeboid Protist
reference: chapter 4 in textbook
A ciliated protist
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
Proposed mechanism of psuedopodial movement. In endoplasm, actin subunits are bound to regulatory proteins that keep them from assembling.
Source: Hickman et al 2001
External Structures for Support and Protection
Forams; shells are made from protein hardened with calcium carbonate
Amoeba; shell made of cemented sand grains
Radiolarians; glassy skeletons allow light penetration for photosynthetic endosymbionts
Diatoms
foraminiferan with calcium carbonate tests
diatomshave glass-like silicon containg sructures
Dinoflaggelates surrounded by cellulose plates
Sources: Purves et al (2002), Freeman (2002)
Multicellularity
Clamydomonas Gonum Pandorina Volvox
Multicellular Green Alga (Coleochaete orbiculairs)
Morphological continuum in Volvocales from unicellular to multicelluar.
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
Source: Freeman 2002
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
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
Gametophytes (n)
Sporophytes (2n)
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
2.5 um 80 um
Margulis webpagewww.bio.umass.edu/faculty/biog/margulis.html
Lynn MargulisU. Mass., Distinguished Professor and Member of the National Academy of Science – developed endosymbiotic theory
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
http://www.malaria.org/lifecycle.html
P. falciparum is the most widespread and dangerous of the four: untreated it can lead to fatal cerebral malaria.
Infected Red Blood Cells
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 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
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 fertilizationoccurs 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
Merozite
Apex
Red blood cell0.5 um
Plasmodium Infection InterpretationStrain Rate
cp26 Low
cp29 LowHLA-B53 binds to these proteins. Immune resonse is effective
cp26 and cp29 strains together
HighImmune response fails when these strains infect the same person
cp27 Highcp28 Average HLA-B53 does not bind to these
proteins. Immune response is not as effective
Co-evolutonary Arm RaceStrong 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
HUMAN IMMUNE-DEFENSE AGAINST PLASMODIUM
Source: Freeman 2002
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