Bio153S: lecture 8
Origin of the eukaryotes
Eukaryotic cell:
• membrane bound organelles
• endoplasmic reticulum
(rough and smooth)
• cytoskeleton
• often without cell wall
• nucleus; DNA in
chromosomes
• complex flagellum
• sex common
how did eukaryotes arise?
• prokaryotic cell
• loss of cell wall; infolding
of cell membrane to
increase SA
• vesicles; some studded
with ribosomes
• nucleus; cytoskeleton
• flagellum for locomotion
evolution of
mitochondria:
advantage:
higher yield of
ATP
(respiration >
fermentation)
flagella and cilia
• eukaryotic flagella and cilia : > 500 types
of proteins
• more complex than prokaryote flagella
“9 +2” microtubule structure
loss of cell wall & infolding of cell
membrane (enclosing nucleus; ER, Golgi
apparatus, lysosomes)
evolution of chloroplasts:
• engulfed cyanobacteria
• capable of oxygenic
photosynthesis
• lamellar structure
(thylakoids) similar in
free-living cyanobacteria
and chloroplasts
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evidence for endosymbiosis
hypothesis:
1. mitochondria & chloroplasts about the
right size to be bacterial cells
2. replicate by fission
3. have own genomes (circular
chromosome), ribosomes; make own
proteins
4. have double membranes
5. affected by antibiotics (don’t affect
eukaryotic cells)
2° endosymbiosis:
in some lineages, a
protist engulfed
another protist!
• chloroplast has 4
membranes
• in some, 3
membranes (1 lost)
The protists
proto = first
all eukaryotes that are not
animals
plants
fungi
chloroplasts have 3
or 4 membranes
chloroplasts have
2 membranes
• no shared, derived characters unique to
protists
• all live in moist or aquatic environments
ecological importance:
• important in aquatic food chains
plants, animals, fungi “embedded” with
protist lineages
paraphyletic
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protists are
morphologically
diverse
table 28.2
functionally diverse:
sessile or motile
autotrophic or heterotrophic
unicellular, colonial, multicellular
parasitic or free-living
sexual or asexual……
tremendous diversity in size:
unicellular protists:
Micromonas pusilla
(1-3 µ)
Pelomyxa palustris
(3 mm)
Pelomyxa is 1,000 X as long;
(1,000)3 = 109 as heavy as
Micromonas
reproduction: evolution of sex
by comparison: blue whale
(190 tonnes) is
only 108 X as heavy as a 2 g
shrew!
multicellular protists: 100m!
• production of genetically unique offspring
• many types of life cycle in protists
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evolution of multicellularity:
• true multicellularity: differentiation of
function; complex cell-cell signalling
• evolved several times
primitive protists: Excavata
•
•
•
•
diplomonads and parabasilids:
lack plastids; mitochondria
2 nuclei; asexual
multiple flagella
Giardia
Trichomonas
major lineages of protists:
•
•
•
•
•
•
•
•
Excavata
Discicristata
Alveolata
Stramenopila
Cercozoa
Plantae?? – algae + land plants
Opisthokonta (includes fungi and animals)
Amoebozoa
Discicristata
Euglenoids and Kinetoplastids:
• unusual mitochondria (disc
shaped cristae)
• unusual flagella (cristalline rod)
• autotrophic (chloroplasts) or
heterotrophic
Euglena
Trypanosomes
Discicristata: kinetoplastids:
• single large mitochondrion
• Trypanosomes: human pathogen
• change cell-surface antigens to avoid
immune response
• 1/3 of genome codes for these proteins
Sleeping sickness
Rhodnius
Chagas disease
4
Leishmania
(trypanosome)
produces many forms
of ulcers & lesions
Alveolata:
• dinoflagellates, apicomplexans and
ciliates
• have sacs beneath plasma membrane
have internal
plates
of cellulose
1. dinoflagellates:
2. apicomplexans:
• e.g. malaria : Plasmodium spp.
• 300 million affected; 1 – 1.5 million die
every year
• “red tide” – neurotoxins
• many are bioluminescent
• 1° productivity in oceans
3. ciliates
Anopheles spp.
mosquito borne
ciliates have contractile vacuoles
• most complex cells on earth!
• 2 types of nuclei: micronucleus &
macronucleus
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Stramenopila
1. Oomycota:
•
•
•
•
“water molds”
like fungi (but have cellulose, not chitin)
potato blight caused Irish famine 1845
e.g. Saprolegnia :
• all have flagella covered with “hairs”
• contain Oomycota, diatoms, brown algae
2. diatoms:
• may harbor photosynthetic
endosymbionts
• in ocean: ~½ global photosynthesis!
• glassy shells
other multicellular algae
• red, golden, green
• monophyletic group including land plants?
3. brown algae
• all species
multicellular
• photosynthetic
& sessile
• reproductive
cells are motile
Cercozoa
Foraminifera:
shelled amoebae
test = shell
pseudopodia emerge
through holes in test
experiments in multicellularity
carbon sink: make up much of debris on
ocean floor
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Amoebozoa
• amoeba, slime molds
• move by
pseudopodia
1. lobose amoebae
2. slime molds
• 2 types: plasmodial and
cellular
• plasmodium: huge
mass of cytoplasm with
many nuclei
• cytoplasmic streaming
• fruiting bodies
cellular slime molds:
• when food abundant: solitary cells
• food scarce: form aggregates; function
as unit
• form fruiting bodies
• potential for conflict:
who forms sterile stalk?
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