Transcript Powerpoint - mrdvorsky

Eukaryotic Evolution and Diversity
Introduction to Protists
Learning Goals
• Understand theory of endosymbiosis in the
evolution of eukaryotes
• Provide evidence for the theory of
endosymbiosis
• Distinguish between the 3 groups of
protists (animal; fungus; plant-like)
Origin of Eukaryotes
• First eukaryotic organism thought to have
evolved about 1.5 billion years ago.
Prokaryotes are as old as 4 billion years
• Protozoans (protists) possibly evolved from the
1st eukaryotes by Endosymbiosis
• Endosymbiosis –theory that explains how
eukaryotic cells evolved from the symbiotic
relationship between two or more prokaryotic
cells; often one prokaryote lives inside another
becoming dependent upon each other
Endosymbiotic Theory
• First postulated by Lynn Margulis in 1967
• Although now accepted as a well-supported
theory, both she and the theory were ridiculed
by mainstream biologists for a number of
years. Thanks to her persistence, and the large
volumes of data that support this hypothesis
gathered by her and many other scientists over
the last 30 years, biology can now offer a
plausible explanation for the evolution of
eukaryotes.
Endosymbiosis wha???
• Endo = "within“
• Endocytosis = (cyto = cell) a process of 'cell
eating' - cells are engulfed, but then usually
digested as food....
• Endosymbiosis = cells are engulfed, but not
digested...cells live together in a mutually
benefiting relationship, or symbiosis
Origin of Eukaryotes
• Eukaryotic cells more complex than
prokaryotic cells:
– Membrane-bound nucleus and organelles
– Many chromosomes that occur in pairs.
– Protists, fungi, plants & animals are
composed of eukaryotic cells.
Eukaryotic Animal Cell
Typical Animal Cell
Eukaryotic Plant Cell
Typical Plant Cell
Origin of Eukaryotes
Endomembrane infolding
Infolding of membrane
system forming nucleus
and ER
Origin of Eukaryotes: Cholorplasts and
Mitochondria
• Mitochondria and chloroplasts
(endosymbionts) were prokaryotes that
invaded larger cells (host cell)
• Mitochondria provided energy for the host cell
and chloroplasts converted solar energy into
molecular energy
• Endosymbiont, ancestral mitochondria:
– Aerobic, heterotrophic & prokaryotic
• Endosymbiont ancestral chloroplasts:
– Anaerobic, autotrophic and prokaryotic
Origin of Eukaryotes
• Ancestral chloroplasts were photosynthetic,
prokaryotes that became endosymbionts
(cyanobacteria)
• Relationship began as parasitic or undigested
prey
• Assumed here that endomembrane infolding
evolved first, i.e., cell already evolved nucleus,
ER, …
Endosymbiosis Hypothesis
A
A prokaryote ingested some aerobic bacteria. The
aerobes were protected and produced energy for
the prokaryote
A
Aerobic bacteria
C
B
Mitochondria
D
Cyanobacteria
Chloroplasts
N
N
N
Plant cell
Prokaryote
N
Animal Cell
Endosymbiosis Hypothesis
Over a long period of time the aerobes
became mitochondria, no longer able to
live on their own
B
A
Aerobic bacteria
C
B
Mitochondria
D
Cyanobacteria
Chloroplasts
N
N
N
Plant cell
Prokaryote
N
Animal Cell
Endosymbiosis Hypothesis
C
Some primitive prokaryotes also
ingested cyanobacteria, which contain
photosynthetic pigments
A
Aerobic bacteria
C
B
Mitochondria
D
Cyanobacteria
Chloroplasts
N
N
N
Plant cell
Prokaryote
N
Animal Cell
Endosymbiosis Hypothesis
Cyanobacteria became chloroplasts,
unable to live on their own
D
A
Aerobic bacteria
C
B
Mitochondria
D
Cyanobacteria
Chloroplasts
N
N
N
Plant cell
Prokaryote
N
Animal Cell
Scientific Evidence for Theory of
Endosymbiosis
• Membranes of chloroplasts and mitochondria are similar
to those of living prokaryotes
• The ribosomes found in these organelles are more
similar to prokaryotic ribosomes than to ribosomes found
in eukaryotes
• These organelles reproduces by binary fission within the
cell
• Each organelle contains a circular chromosome and
gene sequences match those of living prokaryotes
Multicellularity
• Endosymbiosis does not
explain multicellularity,
another eukaryotic
advance
• First multicellular
organisms existed 1.2 to
1.5 billion years ago (or
half as long as unicellular
organisms) Red Algae
• Large complex eukaryotes
fist developed 550 million
years ago
Red Algae fossils
Life Cycles and Reproduction
• Eukaryotes also have more diverse life cycles than
prokaryotes
• In prokaryotes cell division and reproduction are the
same thing: Asexual
• In multicellular eukaryotes cell division ≠ reproduction
• In sexual reproduction, two individuals make eggs and
sperm knows as gametes
• Gametes are haploid (one set of chormosomes,
ha=half) compared to cells of the rest of the organism;
diploid (both sets of chromosomes, di=2)
Asexual Life Cycle
• All prokaryotes
• Some eukaryotes
(yeast)
Gametic Sexual Life Cycle
• Organism is diploid
• Produces haploid
gametes which are
fertilized (zygote)
• Zyogote undergoes
mitosis (cell division)
to become organism
– Humans
Zygotic Sexual Life Cycle
• Organism is haploid
• Produces haploid gametes that
upon fertilization form diploid
zygote
• Zygote undergoes meiosis to
produce haploid spores that
develop into organism
• Most fungi
• Some protists (malaria parasite
Sporic Sexual Life Cycle
• Organism lives in 2 stages: diploid
and haploid
• Haploid organism produces
haploid gamete
• Zygote undergoes mitosis to
become diploid organism
• Diploid organism produces
haploid spores
• Haploid spores become haploid
organism
Protists: The Unicellular Eukaryotes
General Characteristics
• All are eukaryotic, mostly single-celled microscopic
organisms
• Come in all shapes, sizes and colours
• Some have cell walls, some are motile
• Classified together because they do not fit into other
kingdoms, rather than because they are similar or closely
related to one another
• Most diverse group of eukaryotes, but not as diverse as the
bacteria or archaea
• 3 main groups of protists, characterized by how they get
their nutrients.
Three groups of protists
• Animal-like protists
• Fungus-like protists
• Plant-like protist
Animal-like Protists
• (Protozoa) – e.g. Amoebas
– Consume other organisms for food
– Some species are parasites
Protozoa
• Means first animals
• Scavengers or predators
• Some are parasites.
• Vary in shape and size.
• Most live as single cells
but others form colonies
The Cercozoans: Phylum Cercozoa
• Amoebas
• Cell membrane w/o cell wall, so can change
shape
• Can form cytoplasmic extensions called
pseudopods (false feet) for feeding and
movement
• http://www.youtube.com/watch?v=7pR7TNzJ_pA
The Ciliates: Phylum Ciliophora
• Paramecia
• Have many short hair-like projections called cilia
(singular cilium)
• move by cilia beating in a coordinated rhythm, they
also help move food into the paramecium’s gullet,
which leads to a food vacuole.
• http://www.youtube.com/watch?v=fh_yjLppNAg&
feature=fvwrel
Flagellates: Phylum Zoomastigina
• Have one or more flagella which whip from side
to side to move them about
• some are mutualistic: Trichonympha live in
digestive systems of termites and help break
down cellulose.
• some are parasitic: Trypanosomia causes
African sleeping Sickness
• http://www.youtube.com/watch?v=9duvzqvVflw
The Sporozoans: Phylum Sporozoa
• Parasites
• they have spores at some point in their
lifecycle
• they contain a number of complex organelles
at one end of their bodies to help them invade
their victim. Plasmodium vivax causes one
type of malaria in humans
Life Cycle of Malaria-causing Plasmodium
http://highered.mcgraw-hill.com/olc/dl/120090/bio44.swf
Fungus-like Protists
• – e.g. Slime moulds, water moulds
– Absorb nutrients from other organisms (living
or dead)
– Some consume other organisms, some are
parasites
Slime and Water Moulds
• Have the characteristics of
fungi, protozoa and plants.
• They glide from place to place
and ingest food like protozoa.
• They have cellulose in their
cell walls like plants. They
also absorb nutrients from
their environment like fungi.
Plasmodial Slime Moulds (Myxomycotes)
• Visible to the naked eye as tiny slug like
organisms that creep over damp, decaying
plant material in forests and fields.
• This blob, called a plasmodium, contains many
nuclei. Feed in a similar manner to amoebae.
• http://www.youtube.com/watch?v=khEAZabMtO
k&feature=related
Cellular Slime Moulds (Acrasiomycota):
• exist as individual amoeboid like cells with one
nucleus each.
• Feed by ingesting tiny bacteria or yeast cells.
• When food becomes scarce, the cells release a
chemical that causes them to gather together to
form a pseudoplasmodium. This is a jelly-like
mass, which produces a sporangia that
releases spores.
Water Moulds (Oomycota):
• includes water moulds, white rusts and downy
mildews
• Filamentous organisms that resemble fungi.
Most live as saprotrophs (dead organic matter)
• some are parasitic on plants, insects and fish.
They extend fungus like threads into their host
where they release digestive enzymes and
absorb the nutrients.
• Cause of the Irish Potato Famine.
Plant-like Protists
• e.g. Diatoms and dinoflagellates
– Make their own food by photosynthesis
– Some can consume other organisms when
light is unavailable
Diatoms: Phylum Chrysophyta
• most abundant unicellular algae in the oceans. They are
one of the biggest components of plankton.
• Can reproduce asexually. Sexual reproduction is less
common
• As photosynthetic organisms they are also a major source
of atmospheric oxygen. They have rigid cell walls that
contain silica, a common ingredient in sand and glass.
• The remains of diatoms stick around for a long time and
they are used in filters, sound proofers, insulation and as a
gentle abrasive in metal polishes and toothpastes.
Diatoms
Dinoflagellates: Phylum Pyrophyta
• Unicellular, photosynthetic and mostly marine.
• They have protective coats made of stiff cellulose
plates. They all have two distinct flagellae
• They are extremely numerous and form an important
base for marine food chains. Form red tides which
cause toxins to built up in shellfish that eat them.
Red Tide
Some bioluminescence
http://www.youtube.com/watch?v=
Py-J1ZazHDM&feature=fvwrel
Euglenoids
• Unicellular freshwater organisms with two
flagellae, one usually much longer than the
other.
• They contain chloroplasts but if there is no
sunlight then they lose their chloroplasts and
ingest and eat food.
• Have a light receptor and allows them to move
towards light
Homework
• Pg 69, Q 13-18
• Pg 76, Q 19-24
2.3 and 2.4 of the textbook