lecture viii protistans. surface waters teem with microscopic protists in some near-shore areas,...
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Lecture VIII Protistans
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 are the 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
Choanoflagellida Flagellate protists. Possible ancestor to Sponges – to Animals.
Source Solomon et al 2002
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
Giardia, a unicellular human parasite
giant 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 a and phycobilins
Brown: chlorophyll a and 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 phylogenetic diversification
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
Interrelated cytoskeletal functions
-maintain cell shape
-provide for cell movement
-serve as tracks for motor proteins
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
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
External Structures for Support and Protection
Amoeba; shell made of cemented sand grains
Radiolarians; glassy skeletons allow light penetration for photosynthetic endosymbionts
Diatoms
foraminiferan with protein-hardened, calcium carbonate tests
diatoms have glass-like silicon containg sructures
Dinoflagelates surrounded by cellulose plates
Sources: Purves et al (2002), Freeman (2002)
White Cliffs of Dover are limestone composed almost entirely of protistan fossil shells, including forams and coccolithophores (an alga)
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
Life cycle of a diploid species in which the multicellular organism is diploid
Life cycle of a diploid species in which the multicellular organism is haploid
Life cycle of a diploid species in which there is an alternation of generations of multicelluar form – 1n gametophye and 2n sporophyte
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
http://megasun.bch.umontreal.ca/protists/chlamy/introduction.html
http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html
Life Cycle of Chlamydomonas Inset shows mature cells before reproduction
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 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 webpage www.bio.umass.edu/faculty/biog/margulis.html
Lynn Margulis
U. 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 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
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 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
HUMAN IMMUNE-DEFENSE AGAINST PLASMODIUM
Source: Freeman 2002
extra slides
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 global eukaryote phylogeny based on presence or (ancestral) absence of mitochondria, and shape of mitochondrial cristae. Chlamydomonas belongs to the flattened clade.
Postulated phylogenetic position of Chlamydomonas, inferred from molecular and morphological data. Branch lengths are arbitrary and do not
reflect phylogenetic distance.
Extra Slides
Life Cycle of a cellular slime mold (Dictyostelium)
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)
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