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
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.
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
Paramecium
giant kelp
Giardia, a unicellular human parasite
Parasitism
Predation and Scavenging
pseudopodia engulf food
Symbiosis
host
symbionts
Green cells are
dinoflagellates inside a
heliozoan
Ciliary currents sweepd food into
gullet
host
parasite
the parasite is a red
algae – with
nonpigmented cells
Photosynthetic pigments
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)
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
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 have
glass-like silicon
containg sructures
Diatoms
Dinoflagelates
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
Clamydomonas
Gonum
Pandorina
Multicellular Green Alga
(Coleochaete orbiculairs)
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 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
http://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
Life Cycle of Chlamydomonas
Inset shows mature cells before
reproduction
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.
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
Sporophytes (2n)
Gametophytes (n)
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
Life cycle of Laminaryia: an example of alternation of generations
The zygotes grow into new
sprorophytes, starting life attached
to the remains of the old female
gametophyte
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
Proteobacteria
80 um
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.
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
Plasmodium
Strain
Infection
Rate
cp26
Low
cp29
Low
cp26 and cp29
strains together
cp27
cp28
High
High
Average
Interpretation
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
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
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
Life Cycle of a cellular slime mold (Dictyostelium)
Each zoosporangium produces
about 30 biflaagellated zoosppres
asexually
Life Cycle of a cellular slime mold (Dictyostelium)