Evolution of Microbial Life
Lectures 16 and 17
Much of the text material in the lecture notes is from our textbook,
“Essential Biology with Physiology” by Neil A. Campbell, Jane B.
Reece, and Eric J. Simon (2004). I don’t claim authorship. Other
sources were sometimes used, and are noted.
2
Outline
•
•
•
•
•
•
•
•
•
•
•
Brief history of early life
Oxygen revolution
Evolution of cells
Spontaneous generation and biogenesis
Four-stage hypothesis of the origin of life
Prokaryotic microorganisms
Eukaryotic microorganisms
Chemical cycling and the cycle of life
Eukaryotic microorganisms
Origins of multicellular life
Words and terms to know
3
A brief history of early life
4
When the Earth Was Young
•
•
•
•
•
Our solar system formed about 4.5 billion years ago—the universe is
about 13.7 billion years old.
Earth’s crust began to solidify about 4 billion years ago when its interior
started to cool.
Prokaryotic organisms inhabited Earth as early as 3.5 billion years ago.
Within the next billion years two distinct groups of prokaryotes, archaea
and bacteria, diverged.
These early organisms formed rapidly, leading to evolutionary development of many species.
5
Timeline
Years before present
Early episode
475 million
Plants and fungi colonize land
570 million
All major animal phyla established
1 billion
First multicellular organisms
1.7 billion
Oldest eukaryotic fossils
2.5 billion
Accumulation of atmospheric oxygen
3.5 billion
Oldest prokaryotic fossils
4.5 billion
Earth formed
‘Before present’ is defined as 1950 A.D.
6
Fossilized Prokaryotes
Central and southern India
http://www.lisc.ernet.in
The oldest prokaryotic fossils are estimated to be 3.5 billions years old.
7
Oxygen Revolution
•
•
•
•
•
An oxygen revolution began on our planet about 2.5 billion years ago.
Photosynthetic prokaryotes that split water molecules released large
amounts of oxygen gas (O2), changing the composition of the atmosphere.
O2 doomed many other prokaryotic organisms because of its oxidizing,
corrosive effects.
A diversity of metabolic modes evolved among the surviving organisms,
including cellular respiration in eukaryotic cells that uses O2 to extract
energy from food.
Metabolic evolution occurred during a period of almost two billion years
when only prokaryotes existed.
8
Cyanobacteria
http://www.unm.edu
Cyanobacteria are photosynthetic form
of bacteria.
9
Components of a Prokaryotic Cell
http://desertfiddlekate.blogspot.com
Much simpler in structure than eukaryotic cells.
10
Earliest Eukaryotic Cells
Eukaryotic cells formed almost two billion years after the first prokaryotic
cells—the oldest eukaryotic fossils are about 1.7 billion years old.
• Eukaryotic cells evolved from prokaryotic cells that hosted even smaller
prokaryotes.
• The mitochondria and chloroplasts in eukaryotic cells are the evolutionary
descendents of these tiny hitchhikers.
•
11
Protists
The earliest eukaryotic forms are protists—they are mostly microscopic
and unicellular.
• Protozoa and single-cell algae (such as diatoms) are a few examples of
protists.
• We will discuss several forms of protists found on the Earth today in this
lecture.
Diatoms
http://www.digitalstar.net/microecologies
•
12
Prokaryotic vs. Eukaryotic Cells
•
•
•
•
•
•
Prokaryotic cells are about one-tenth the size of eukaryotic cells—their
volume is about 103 smaller.
Prokaryotic cells are much older in an evolutionary sense—3.5 billion vs.
1.7 billion years for eukaryotic cells.
Most prokaryotes have a cell wall exterior to their plasma membranes—
these walls are chemically different to the cellulose walls of plant cells.
Prokaryotic cells are structurally much simpler—the internal components
generally lack membranes.
Prokaryotic cells also lack a membrane-enclosed nucleus—the DNA is
coiled in a nucleoid region that is not partitioned from the rest of the cell.
Prokaryotic cells can be compared to open warehouses while eukaryotic
cells are more like modern offices partitioned into cubicles.
13
Multicellular Organisms
The next great evolutionary step for eukaryotic cells was the formation
of multicellular organisms that first evolved about one billion years ago.
• Modern descendants include multicellular protists such as seaweeds.
• Other evolutionary paths diverging from the early protists lead to fungi,
plants, and animals.
•
14
Cambrian Explosion
The greatest diversification of animals happened during the Cambrian
explosion.
• The Cambrian period was the first period of the Paleozoic era beginning
about 570 million years ago.
• The earliest animals lived in the Pre-Cambrian seas—they diversified
extensively over a span of about 10 million years in the early Cambrian
period.
• The major body plans of animals,
known as phyla, had evolved by
the end of the Cambrian period.
Cambrian sea life
http://www-eaps.mit.edu
•
15
Colonization of Land
Life was confined to aquatic environments for about the first three billion
years of biological history.
• Plants, in the company of fungi, began colonizing land about 475 million
years ago.
• Today, the roots of most plants are aided by fungi that help absorb water
and minerals from the soil—without these fungi most life would not exist.
• Plants transformed the terrestrial landscape and created opportunities
for all life forms including plant-eating (herbivorous) animals and their
predators.
•
16
Colonization of Land
Vertebrates (animals with a spine), in the form of amphibians, ventured
out of the water.
• Frogs and salamanders are descendants of air-breathing fish with fleshy
fins that could support their weight on land.
• Reptiles later evolved from amphibians, and birds and mammals evolved
from reptiles.
•
17
How did life first originate?
18
Origin of Life
We may never know with certainty of how life first began on our planet.
• We can start, however, with the assumption that science seeks natural
causes for natural phenomena.
•
Artist’s depiction of single-cell organisms on the early seafloor
near volcanic vents
http://www.lpi.usra.edu
19
Spontaneous Generation
•
•
•
•
•
From the time of ancient Greek civilization, life was thought to arise from
non-living matter.
The process of life emerging from non-life is called spontaneous generation.
The idea persisted into the mid-1800s to explain the presence of microorganisms in food.
Then, Louis Pasteur demonstrated in experiments in 1862 that microbes
arise from the reproduction of existing life.
The life-from-life principle is known as biogenesis—since Pasteur’s work
it has been extended to all forms of life.
20
Pasteur’s Experiments
Could microorganisms
spontaneously form and
thrive in an environment not
exposed to air?
http://www.morning-eart.org
Louis Pasteur (1822-95)
http://www.darwin.museum.ru
21
Biogenesis
•
•
•
•
•
•
Since life did not always exist how did the first organisms arise from nonliving matter?
No evidence exists today for spontaneous generation, but conditions on
a young Earth were very different.
The primordial atmosphere contained very little O2 to oxidize and breakdown molecules.
Energy sources—including volcanoes, lightning, and ultraviolet light from
the sun—were more intense than today.
Many biologists think it possible that physical and chemical processes in
the early environment could have produced the first cells.
Although there is general agreement about the outline of how life first
formed, debate continues about the sequence of steps in producing the
first life forms.
22
Early Energy Sources
http://cas.hamptomu.edu
http://www.air-and-space.com
The sun’s ultraviolet spectrum
http://earthobservatory.gov
23
Four-Stage Hypothesis
•
•
•
•
•
The first organisms may have been products of chemical changes that
occurred in four stages.
Stage 1: Abiotic or non-living synthesis of small organic molecules such
as amino acids and nucleotides.
Stage 2: Small organic molecules joined into polymers such as proteins
and nucleic acids.
Stage 3: Self-replicating molecules formed, eventually making genetic
inheritance possible.
Stage 4: The molecules formed into pre-cells, droplets with membranes
that have an internal chemistry distinct from the external environment.
The four-stage hypothesis leads to predictions that can be tested
in the laboratory.
24
Stage 1
•
•
•
•
•
Stanley Miller constructed a laboratory apparatus in 1953 that simulated
atmospheric and sea conditions that may have occurred on early-Earth.
Similar experiments were performed at about the same time by Harold
Urey.
Miller’s apparatus produced small organic (carbon backbone) molecules
including amino acids essential for life—amino acids are building blocks
for proteins
Other scientists extended the research by varying the conditions of the
artificial atmosphere and sea.
Organic molecules produced in a number of experiments included all 20
amino acids, sugars, lipids, and the nucleotides found in DNA and RNA.
25
Miller-Urey Experiments
Methane molecule
http://classweb.smu.edu
http://www.kennislink.nl
Miller’s laboratory apparatus
http://ucsdnews.ucsd.edu
26
Other Origins
Some organic compounds found on Earth may have extraterrestrial
origins.
• Computer simulations have demonstrated how adenine (a molecule in
DNA) may have formed in chemical reactions of cyanide in gas clouds
of interstellar space.
• These simulations would explain why meteorites found on earth contain
organic molecules.
•
Meteorite on display
http:www.grisda.org
27
http://www.rpi.edu
Primordial Soup
Add energy?
28
Stage 2
Experiments were conducted to determine if organic molecules could
have formed into polymers without the assistance of enzymes found in
living cells.
• The synthesis of polymers has been shown to occur when organic
monomers in an aqueous (water) solution are dripped onto hot sand,
clay, or rock.
• Heat vaporizes the water in the solution and concentrates monomers
on the hot substrate.
• Some of the monomers bond to form polymers, including polypeptides
from amino acids.
•
29
Stage 2
On early-Earth, rain may have splashed inorganic molecule solutions
onto fresh lava.
• These newly-formed polymers could then have been washed into the
oceans.
• Abiotic synthesis may have occurred near deep sea vents that emitted
hot gases and superheated the water.
•
Deep sea vent
http://fti.need.wisc.edu
30
Stage 3
The definition of life is partly based on inheritance, which is based on
self-replicating molecules.
• Cells store their genetic information as DNA, which is transcribed to
RNA and then translated to specific proteins.
• These mechanisms probably emerged through a long series of refinements to much simpler processes.
•
31
First Genes?
•
•
•
•
•
The first genes may have been short strands of RNA that could replicate without the assistance of enzymes formed from proteins.
Laboratory experiments have demonstrated that short strands of RNA
can assemble spontaneously from nucleotides without the presence of
enzymes.
The result is a population of RNA molecules of random sequences of
nucleotides monomers.
On early-Earth, some of these RNA strands may have replicated with
varied success resulting in molecular evolution on a very small scale.
In keeping with the principles of natural selection, the RNA molecules
that replicated the fastest increased their frequency in the population.
32
Stage 4
•
•
•
•
•
Properties of life emerged from interaction of molecules self-organizing
into higher levels of order needed to form pre-cells and then living cells.
RNA strands and polypeptides may have cooperated inside a simple
membrane.
Physical processes needed for cellular functioning, including osmosis
and voltage differences, would have been possible.
Some molecular aggregates became pre-cells that contained some of
the properties of life.
One property is a rudimentary metabolism of absorbing molecules from
the surroundings and releasing products of their reactions.
33
Chemical to Darwinian Evolution
Mutations produced variations in the populations of pre-cells—the most
successful pre-cells would have continued to grow, divide, and evolve.
• Molecular cooperatives of pre-cells could have become more cell-like
after many millions of years of refinement through the natural selection
process.
• The point at which pre-cells, with their rudimentary metabolism and
genetic instructions, became actual living cells is not clear and may
never be known.
• However, life in the form of prokaryotes was in abundance 3.5 billion
years ago—all other branches of life arose from these earliest cells.
•
34
Prokaryotic Microorganisms
35
Prokaryotes
Prokaryotic cells evolved as the only form of life on Earth for almost two
billion years.
• Prokaryotes have continued to adapt and flourish on an evolving Earth,
and have helped to change our planet.
• We will explore this diversity and adaptation in the next sections of this
lecture.
•
36
Where They Live
Today, prokaryotes are found wherever life exists—they outnumber all
eukaryotes combined.
• The bacteria inhabiting a handful of fertile soil or the skin or mouth of a
human can number in the billions.
• Some prokaryotes thrive in habitats too hot, cold, acidic, or alkaline for
eukaryotes to survive.
• For example, prokaryotes were found in a goldmine almost two miles
below the Earth’s surface.
•
37
Bacteria in Soil
http://soils.usda.gov
One teaspoon of soil contains 100 million to one billion
bacteria. The bacteria on an acre is equivalent to the
mass of up to two cows.
38
Collective Impact
Although very small organisms, prokaryotes collectively have a substantial impact on life.
• The bacterial disease, bubonic plague (also known as the the black
death) killed at least 25 percent of Europe’s population during the 14th
century.
• Tuberculosis, cholera, many sexually-transmitted diseases, and some
types of food poisoning are caused by bacteria.
•
The Black Death
http://upload.wikimedia.org
39
Bacteria on a Pin Head
Electron micrograph
http://faculty.ccri.edu
40
Beneficial Roles
•
•
•
•
•
•
However, bacteria that have beneficial roles are more common than
harmful bacteria.
Bacteria in our intestines aid in digestion and other bacteria prevent
harmful fungi from inhabiting our mouths.
Bacteria that decompose dead organisms are found in the soil, and in
the bottoms of rivers, lakes, and oceans.
Decomposers return chemical elements to the environment in the form
of inorganic compounds that can be used by plants, which in turn feed
animals directly or indirectly.
If decomposers were to disappear, the chemical cycles that sustain life
would stop, and eukaryotic life could not survive.
Prokaryotes would continue to survive as they had during the first ~ 1.7
billion years of life.
41
Prokaryotic Evolution
•
•
•
•
•
The five-kingdom classification is based on fundamental differences in
cellular organization between prokaryotes and eukaryotes.
Prokaryotes make-up the kingdom Monera separate from the eukaryotic
kingdoms of Protista, Fungi, Plantae, and Animalia.
The branches of prokaryotes are archaea and bacteria—the branches
were established by comparing genomes.
Archaea and bacteria also differ in many of their structural, biochemical,
and physiological characteristics.
Archaea are more related to eukaryotes than bacteria, which has led to a
newer three-domain classification of Bacteria, Archaea, and Eukarya.
42
Extremophiles
The majority of prokaryotes are bacteria—archaea occupy evolutionary
and ecological niches.
• Biologists often refer to some archaea as extremophiles, or lovers of
the extreme (phile = love).
• Extreme halophiles (salt lovers) thrive in the Great Salt Lake and in
salt-evaporating ponds where salinity is well above that of the oceans.
• Extreme thermophiles (heat lovers) live in very hot water such as deepsea vents that produce superheated water.
•
43
Salt Evaporation Ponds
http://fig.cox.edu
Archaea thrive in high-salinity conditions, producing
the yellow and red colors in the evaporation ponds.
44
Hydrothermal Sea Vents
Sea vents are typically located in
oceanic spreading zones
http://www.is.tokayu.ac.jp
The underlying hot magma
superheats the seawater.
http://www.mbary.org
45
Another Class of Extremophiles
Some archaea live in anaerobic environments and give-off methane
(CH4) as a waste product.
• These methanogens living in the mud of lakes and swamps produce
methane-rich marsh gas—some instances may have been resulted
in UFO sightings.
•
http://www.freesteel.co.uk
http://ugos.homestead.com
46
Other Methanogens
Methanogens, most notably bacteria, inhabiting the intestine tracts of
animals can produce bloating and intestinal gas.
• Methanogens also help grazing animals digest the cellulose in plant
walls—the animals emit large amounts of methane through belching.
•
http://www.classohm.com
47
Bacterial Shapes
Cell shape is used as the general classification method for the many
types of bacteria.
• Spherical species are cocci (plural for coccus) from the Greek word for
‘berries.’
- Cocci in clusters are staphylcocci (clusters of grapes), or staph for
short as in ‘staph infection.’
- Cocci in chains are streptococci (twisted grapes)—the bacterium
that causes strep throat is a streptococcus.
•
Rod-shaped species are bacilli (plural for bacillus).
• Spiral-shaped species are spirochetes—the bacterium responsible for
syphilis is a spirochete.
•
48
Bacterial Shapes
The colors reflects the chemical stains used
Bacilli
Cocci
Spirochetes
All images from http://www.bioweb.uncc.edu
49
Cell Organization
Most prokaryotes are unicellular and very small, although there are
exceptions.
• Some species aggregate transiently into groups of like cells, such as
in streptococci.
• Other prokaryotes form permanent colonies of identical, non-differentiated cells.
• Some species of prokaryotes show a simple multicellular organization
and divide labor between specialized types of cells.
•
50
Cell Motility
About half of all types of prokaryotic cells are motile, or self-propelled.
• They may have one or more flagella that can propel them from unfavorable places, or favorable places such as nutrient-rich environments.
•
http://contents.answers.com
51
Endospores
•
•
•
•
•
Few bacteria can thrive in extreme environments favored by archaea.
Some bacteria, however, can survive extended time periods in harsh
conditions by forming resting cells, or endospores—they can remain
dormant for centuries.
Boiling water generally cannot kill these dormant cells.
Laboratory and medical equipment are sterilized using an autoclave
(similar to a pressure cooker) that kills endospores with high-pressure
steam at 250o F, or 121o C.
The food-canning industry uses a similar method to kill endospores of
the soil bacterium Clostridium botulinum that causes botulism, a potentially fatal disease.
52
Endospore
http://dwb.unl.edu
53
Anthrax Endospores
http://www.sciencedaily.com
Bacillus anthracis causes anthrax, an often-deadly disease in
cattle, sheep, and humans. The endospores can survive harsh
conditions. They can absorb water and the bacteria will resume
their growth when conditions are more hospitable.
54
Reproduction Rates
•
•
•
•
•
•
Most prokaryotes can reproduce at very high rates if conditions are
favorable.
The cells copy their DNA almost continuously and divide repeatedly
through binary fission.
If a bacteria could double every 20 minutes, in just 24 hours a single
cell could give rise to a bacterial colony equivalent in mass to 15,000
humans.
Bacteria cannot sustain exponential growth due to limited resources
including food and space, and the waste products from the bacteria
that pollute the colony’s environment.
The rapid and repeated doubling helps to explain why a few bacteria
cells can make us very ill.
Refrigeration (cold) retards food spoilage since most microorganisms
reproduce very slowly at low temperatures.
55
Repeated Geometric Doubling
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
4
8
16
32
64
128
256
512
1,024
2,048
4,096
8,192
16,384
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
32,768
65,536
131,072
262,144
524,288
1,048,576
2,097,152
4,194,304
8,388,608
16,777,216
33,554,432
67,108,864
134,217,728
268,435,456
536,870,912
Would you rather have a million dollars or a dollar that
doubles every day for 30 days?
56
Nutritional Diversity
•
•
•
•
•
The prokaryotic domain has a variety of biological mechanisms for
obtaining nutrition.
Nutrition refers to how an organism obtains energy and carbon for
synthesizing organic compounds.
Phototrophs use light energy; chemotrophs obtain their energy from
their environment; autotrophs need only carbon dioxide for a carbon
source.
Heterotrophs require at least one organic nutrient (such as glucose)
as a carbon source.
All prokaryotes can be grouped according to four modes of nutrition
as shown on the next slide.
57
Modes of Nutrition
Nutritional Type
Energy Source
Carbon Source
Examples
Photoautotroph
(photosy nthesizer)
Sunlight
CO 2
Cyanobacter ia (similar
mechanism to photosynthesis in plants)
Chemo autotroph
Inorga nic chemicals
CO 2
Prokaryotes living near
deep-water heat vents
Photoheterotroph
Sunlight
Organic compounds
Very limited number of
prokaryotes
Organic compounds
Widely used among
prokaryotes (a nd
animals and fungi too)
Chemo heterotroph
Organic compounds
58
Bacteria that Cause Disease
•
•
•
•
•
We are constantly exposed to bacteria, and some species be harmful.
Bacteria and other microorganisms that cause diseases are known
as pathogens.
The body’s defenses, including the immune system, usually inhibit
the growth of pathogens.
Sometimes the balance shifts in the favor of the pathogen, and illness results.
Some of the bacteria that are normally residents in our bodies can
make us ill when our defenses are weakened by a viral infection or
poor nutrition.
59
H. Influenzae Bacterium
The Haemophilus influenzae bacterium resides on the epithelial cells
of the interior of the nose, and can cause pneumonia.
• Malnourished children are particularly susceptible to this bacterium
due to their lowered resistance.
• This bacterium, although similar in name, is not the same as the flu
virus.
•
http://www.brown.edu
60
Exotoxins
•
•
•
•
•
Pathogenic bacteria cause disease by producing poisons—they can
be either exotoxins or endotoxins.
Exotoxins are proteins secreted by bacterial cells—a single gram of
botulism could kill one million people if it were widely dispersed.
The exotoxin producer, Staphylococcus aureus, is a usually harmless resident of the surface of human skin.
Serious disease can result if this bacteria (known as staph) enters
the body through a wound or contaminated food.
S. aureus can produce a variety of effects including sloughing of skin
layers, vomiting, severe diarrhea, and toxic shock syndrome, which
can be deadly.
61
Endotoxins
Endotoxins are chemical components of cell walls of some bacteria.
• All endotoxins produce the same general set of symptoms—fever,
aches, and shock (a dangerous drop in blood pressure).
• The severity of these conditions varies with the host organism and
the type of bacteria.
• Different species of the bacteria Salmonella produce endotoxins that
cause food poisoning and typhoid fever.
•
62
Prevention and Treatment
•
•
•
•
•
Bacterial infections have progressively decreased in many countries
during the past century following the discovery that microorganisms
cause disease.
Bacterial infections can be addressed through sanitation, antibiotics,
and education.
Sanitation methods are the most effective ways to prevent bacterial
disease.
Installation and operation of water treatment and sewage systems is
an effective public health approach.
Antibiotics are used to treat most bacterial diseases, but their widespread use has resulted in the evolution of drug-resistant pathogens,
such as some forms of tuberculosis.
63
Lyme Disease
•
•
•
•
•
•
Lyme disease is caused by a spirochete bacterium carried by ticks
found on deer and field mice.
It is the most widespread pest-carried disease in the United States,
especially in the mid-Atlantic and northeastern states (some cases
have been reported on the West Coast).
Early symptoms of Lyme disease is a red rash shaped like a bull’s
eye encircling a tick bite.
Antibiotics can be used in effectively treating the disease if they are
given within a month of exposure.
If left untreated, Lyme disease can cause debilitating arthritis, heart
disease, and disorders of the nervous system.
The best defense is public education about using insect repellant,
wearing long sleeve shirts and long pants, and seeking treatment if
a characteristic rash develops.
64
http://aapredbook.aappublications.org
Lyme Disease
http://www.lib.uiowa.edu
http://www.nlm.nih.gov
65
Chemical Cycling
•
•
•
•
•
All life depends on the recycling of chemical elements between the
biological and physical components of ecosystems.
Cyanobacteria restore oxygen to the atmosphere and some convert
nitrogen gas in the atmosphere to nitrogen compounds that plants
can then absorb from soil and water.
Bacteria living in the roots of bean plants and other legumes contribute large amounts of nitrogen to the soil.
All nitrogen that plants use in synthesizing proteins and nucleic acids
comes from prokaryotic metabolism.
As consumers, animals must obtain their nitrogen compounds from
plants.
66
The Cycle of Life
Some prokaryotes break down organic waste and dead organisms.
• Through this process of decomposition, prokaryotes return elements
in inorganic forms that can be used by other organisms.
• Carbon, nitrogen, and other essential elements would be locked in
waste products and dead organisms if not for decomposers such as
prokaryotes.
• Life would eventually cease to exist if these essential elements could
not be used.
•
67
Bioremediation
Biologically-diverse prokaryotes are being used in helping to cleanup the environment.
• Use of microorganisms to remove pollutants from water, air, and soil
is known as bioremediation.
•
http://www.alabastercorp.com
68
Abandoned Mine Site
Rocky Mountains, Colorado
http://toxics.usgs.gov
Many long-abandoned mines continue to be
toxic waste hazards.
69
Bioremediation
•
•
•
•
•
Anaerobic prokaryotes are added to solid matter (sludge) produced
from the raw effluent at sewage treatment plants.
The microorganisms decompose the organic matter in the sludge for
use as landfill or as fertilizer after chemical sterilization.
Bacteria that naturally occur on beaches can decompose petroleum
and help clean-up oil spills.
Genetically-engineered bacteria in development to accelerate the
oil-consuming process.
Other bacteria are being genetically-engineered to consume and
deactivate poisonous heavy metals found at old, often abandoned
mining sites.
70
Eukaryotic Microorganisms
71
Pond Water
http://www.georgeloper.org
Walden Pond, Concord, Massachusetts
http://www.visitusa.com
72
Protists
Pond water observed under a light microscope reveals many diverse
organisms known as protists.
• Protists are eukaryotes—even the simplest are more complex than
prokaryotic cells.
• The first eukaryotes composed of single-cell organisms evolved from
prokaryotic cells—multicellular eukaryotes were to follow many millions
of years later.
•
73
Origin of Eukaryotic Cells
•
•
•
•
•
•
Differences between prokaryotic and eukaryotic cells far outnumber
the differences between animal and plant cells.
Fossil records suggest the first eukaryotes evolved from prokaryotes
about 1.7 billion years ago.
A major question, yet to be fully answered, is how eukaryotes first
emerged.
One theory is eukaryotic cells emerged through the combination of
two processes.
In the first process the endomembrane system formed from inward
folding of the plasma membrane in prokaryotic cells.
A second process, endosymbiosis, produced early mitochondria and
chloroplasts.
The endomembrane system includes all membrane-enclosed cells
in the cytoplasm except for the mitochondria and chloroplasts.
74
Endosymbiosis
Symbiosis is a close association between organisms of two or more
species where there is mutual benefit.
• Endosymbiosis refers to a species living within a host species.
• Mitochondria and chloroplasts probably evolved from smaller prokaryotes that established residence within larger host prokaryotic
cells.
•
75
Origin of Mitochondria and Chloroplasts
The ancestors of mitochondria may have been aerobic bacteria that
used oxygen to generate energy in the form of ATP and NADPH.
• Some of the bacteria may have escaped digestion by the larger cell
and continued to perform respiration in support of its host as oxygen
accumulated in the atmosphere.
• Photosynthetic bacteria may have also lived in host cells, and later
evolved into chloroplasts.
• Mitochondria may have developed first since all eukaryotic cells have
mitochondria, but not all have chloroplasts.
•
76
Similarity with Prokaryotic Cells
•
•
•
•
•
Mitochondria and chloroplasts are similar to prokaryotic cells in key
ways.
Both contain DNA, RNA, and ribosomes that resemble prokaryotic
versions.
These genetic components enable mitochondria and chloroplasts to
show some autonomy.
For example, they transcribe and translate their DNA into polypeptides to synthesize their own enzymes.
Mitochondria and chloroplasts also replicate their DNA by a process
resembling binary fission in prokaryotes.
77
Wide Diversity of Protists
•
•
•
•
•
•
Although all protists are eukaryotes they are so diverse they share
few other general characteristics.
Protists vary in structure and function more than any other group of
organisms.
Most protists are unicellular, but some are colonial or multicellular.
Protists are the most complex of all cells since unicellular protists
must be as complete as any plant or animal to perform the functions
necessary for life.
The four major categories of protists are: protozoans, slime mold,
unicellular algae, and seaweeds.
The categories are organized more by lifestyle than by evolutionary
relationships.
78
Star Wars Cantina Scene
http://www.starwarsholidayspecial.com
The diverse world of protists reminds me of this movie scene.
79
Protozoans
•
•
•
•
•
Protists that obtain nourishment by ingesting food are protozoans, or
‘first animals.’
They thrive in all types of aquatic environments including lakes, wet
soil, and the fluid environments inside other organisms.
Most species eat bacteria—some can absorb nutrients dissolved in
water.
Protozoans living as parasites in animals, and cause some of the
world’s most harmful diseases.
Protozoans include flagellates, amoebas, forams, apicomplexans,
and ciliates.
80
Flagellates
•
•
•
•
•
•
This group of protozoans locomote by the means of one or more
flagella.
Most flagellates are free-living and usually not dangerous, but some
are parasitic.
Giardia is a parasite that infects the human intestine and can cause
abdominal cramping and severe diarrhea.
This parasite can be transmitted to humans through drinking water
contaminated with feces from animals.
Other flagellates that are dangerous are the trypanosomes including
a species that causes sleeping sickness.
Sleeping sickness is a debilitating sickness found in parts of Africa; it
is transmitted by the tsetse fly.
81
Prokaryotic Flagella
Connecting mechanism
http://images.encarta.msn.com
Multiple flagella
http://www.sinisia.web1000.com
82
Mountain Stream
http://www.markbsplace.net
Cool, clear water…
http://ehrenfest.anu.edu
Please be sure to
filter it before
drinking!
83
Amoeba
Although amoeba have considerable flexibility and can move rapidly,
they no permanent locomotor organelles.
• Amoeba move and feed by pseudopodia—extensions of the cell
resulting from rapid reconfiguration of protein microtubules in the
cytoplasm.
• Amoeba can assume many shapes as they move among the rocks,
sticks, mud, and other obstacles in ponds, lakes, rivers, and oceans.
•
84
Amoeba
Feeding
Reproduction
(binary fission)
http://www.scientificillustrator.com
Images from
http://www.biology-resources.com
85
Amoebic Diseases
Many species of amoeba are not dangerous to humans—however,
one species can enter the brain through the nasal cavity which can
lead to death in a few weeks.
• In the past few years some fatalities have been reported for swimmers—especially children—in the warm lakes of the southeastern
United States.
• Amoebic dysentery results from an amoebic parasite, which sometimes occurs in countries with poor sanitation.
•
86
Forams
Most forams are marine organisms—that is, they live in the world’s
oceans.
• The cells secrete a porous shell made of organic material hardened
with calcium carbonate.
• Thin strands of cytoplasm (pseudopodia) extend through the pores
of the shell for swimming, feeding, and shell formation.
• The shells of fossilized forams form the limestone rocks found in
some land formations.
•
Limestone
distribution
(shown in yellow)
http://www.reec.nsw.edu
87
Limestone
Fossils embedded
in limestone
Both images from http://upload.wikimedia.org
Limestone cliffs
88
Apicomplexans
•
•
•
•
•
All apicomplexans are parasitic, and some can cause human serious
diseases.
They are named for an apparatus at their apex (apical complex) that
penetrates host cells and tissues.
The apiocomplexan, Plasmodium, causes malaria that infects more
than 200 million people in the tropics each year.
The apical complex is used to enter and feed upon red blood cells of
the human host, eventually destroying them.
Malaria is spread by a few species of mosquitoes—and it is one of
the most debilitating and widespread human diseases throughout
history.
89
http://www.oucom.ohiou.edu
Plasmodium (Malaria) Cycle
90
Malaria Map
http://www.ch.ic.ac.uk
High-risk areas are shown in red.
91
Ciliates
Ciliates use locomotor structures made of proteins, known as cilia, to
move and feed.
• Most are free-living and not parasitic, and therefore pose very little
danger.
• The best known example of a ciliate is Paramecium, found in pond
water.
•
http://www.silkentent.com
92
Paramecium
http://en.wikivisual.com
http://www.cartage.org.lb
93
More Ciliates
http://www.nsf.gov
94
Slime Molds
Slime molds resemble fungi in appearance and ‘lifestyle’ although
they are not closely related—the similarities are due to convergent
evolution.
• Slime molds have filament-like bodies suited for their role of decomposers of organic material.
• The two main categories of slime molds are plasmodial and cellular.
•
95
Plasmodial Slime Mold
Plasmodial slime molds form an amoeboid mass, known as plasmodium, during the feeding stage in their lifecycle.
• Plasmodial slime molds are found among leaves and other decaying
material on forest floors.
• The plasmodium, a single cell with many nuclei, can measure several
centimeters across.
http://www.ppdl.purdue.edu
•
96
Cellular Slime Mold
Cellular slime molds consist of amoeboid-like cells functioning individually to feed on decaying organic matter.
• When the food source is depleted the individual cells aggregate and
form a slug-like colony that moves and functions as a single unit.
• Cellular slime molds raise the question about what it means to be an
individual organism.
•
97
Unicellular Algae
•
•
•
•
•
Photosynthetic protists are called algae—their chloroplasts support
food chains in freshwater and marine ecosystems.
Many unicellular algae are components of plankton (from the Greek
word for ‘wanderer’).
Plankton are communities of mostly microscopic organisms that drift
or swim near the surfaces of ponds, lakes, and oceans.
More specifically, these types of algae are known as phytoplankton
due to their photosynthetic capabilities.
Three groups of unicellular algae are dinoflagellates, diatoms, and
green algae.
98
Dinoflagellates
•
•
•
•
•
Dinoflagellates are photosynthetic protists—they are commonly-found
types of phytoplankton.
Each species has a characteristic shape reinforced by external plates
made of cellulose.
The beating of the two flagella in perpendicular grooves produces the
spinning motion for which they are named (‘dino’ means ‘whirling’ in
Greek).
Population explosions of dinoflagellates cause a phenomenon in warm
coastal waters known as red tide.
Toxins produced by these dinoflagellates can result in massive fish kills,
and can be dangerous to humans too—public health alerts are issued
when red tides are expected.
99
Dinoflagellates
http://cache.eb.com
http://bioweb.uncc.edu
100
Diatoms
Diatoms have clear cell walls containing silca, the mineral used to make
glass—these protists come in many shapes and sizes.
• The glass-like cell walls consist of two halves that fit together as with the
bottom and lid of a shoe box.
• Diatoms store food reserves in oil that provides buoyancy, enabling these
phytoplankton to float near the sunlit surface.
• Very large accumulations of fossilized diatoms make-up thick sediments
known as diatomaceous earth, which is mined for use as filtering material
and an abrasive.
•
101
Multitude of Diatomic Shapes
http://www.botany.hawaii.edu
http://www.micographia.com
102
Centric Diatoms
http://www.nh.ac.uk
103
Diatomaceous Earth
http://epod.usra.edu.de
http://www.ucmp.berkeley.edu
http://www.invisiblegardener.com
104
Green Algae
•
•
•
•
•
Green algae, named for their grass-green chloroplasts, flourish in many
freshwater lakes and ponds.
Some species are flagellated to allow for movement in their through the
watery medium.
Green algae also include colonial forms, such as Volvox—each colony is
a ball of flagellated cells.
The balls-within-balls are daughter colonies that will be released when
the parent colonies rupture.
Of all the photosynthetic protists, green algae are most closely related to
terrestrial plants.
105
Green Algae
http://www.virtualviz.com
Freshwater pond.
106
Volvox
http://www.rbgsyd.nsw.gov.au
Close-up of a single colonial form on the right.
107
Seaweeds
Seaweeds are large, multicelullar marine algae that grow on rock shores
and offshore beyond the zone of pounding surf.
• The cell walls contain a rubbery substance that cushions seaweed from
the agitation of waves.
• Although seaweeds can be as large and complex as terrestrial plants, the
similarities are a consequence of convergent evolution.
• The closest relatives of seaweeds are unicellular algae, which is why they
are classified as protists.
•
108
Human Diets
•
•
•
•
•
Coastal peoples, particularly in Asia, harvest seaweed as food—in Japan
and Korea some species are added to soups and others to wrap sushi.
Marine algae are a source of iodine, to help prevent goiter, and other
minerals too.
Most of the organic material in seaweeds are polysaccharides that cannot
be digested by humans—seaweeds are eaten mostly for their rich tastes
and textures.
The gel-forming substances in the cell walls are used as thickeners in
some processed foods such as puddings, ice cream, and salad dressings.
Agar, a seaweed extract, provides the gelatinous base for the culture of
bacteria in Petri dishes.
109
Green and Red Algae
Seaweeds are classified into three groups (green, red, and brown) in part
based on the types of pigments present in their chloroplasts.
• Green algae often inhabit the intertidal zone between high and low tides—
they are related to unicellular and colonial species of algae.
• Red algae are most abundant in the warm waters of the tropics, and live in
relatively deep water.
• The chloroplasts in red algae have pigments that absorb blue and green
light that penetrates best through water.
•
110
Types of Algae
Red algae
Brown algae
Green Algae
All images from http://taggart.glg.msu.edu
111
Brown Algae
•
•
•
•
•
•
Brown algae include the largest seaweeds, known as kelp—kelp beds are
found along the coast from the Gulf of Alaska to Baja California, and near
the islands in the Southern California Bight.
Some species such as giant kelp can grow linearly over a foot per day and
almost 200 feet in a single year.
Kelp provides rich habitat for many marine species—in some locations the
estimate is over 700 species.
Kelp beds also calm the ocean surface and reduce the pounding of waves
that can erode a shoreline.
Piles of kelp can often be found on Southern California beaches especially
after a storm--the small bladders are gas-filled floats that keep the photosynthetic blades near the ocean’s surface.
Kelp, harvested by boats that cut and collect their tops, can be a renewable
resource if managed properly.
112
Kelp
http://www.onr.navy.mil
Giant kelp, Macrocystis pyrifera
Monterey Bay Aquarium
http://upload.wikimedia.org
113
Kelp Harvesting
Republic of Ireland
http://www.maritimes.ie
Icelandic kelp harvester
Northern California
http://www.thorverk.is
http://montereybay.noaa.gov
114
Origins of Multicellular Life
115
Cellular Complexity
•
•
•
•
•
An orchestra can play a greater variety of musical compositions than a violin
soloist can.
The general concept is that the greater complexity makes more variations
possible.
The origin of the eukaryotic cell led to an evolutionary ‘radiation’ of new life
forms.
Unicellular protists, which are eukaryotic cells, are more diverse in form than
the simpler prokaryotic cells.
The evolution of multicelullar complexes of eukaryotic cells broke through
an even higher threshold in structural organization.
116
Multicellular vs. Unicellular Organisms
Multicellular and unicellular organisms are fundamentally different from one
other.
• All of life’s activities occur within the single cell of a unicellular organism.
• A multicelullar organism, in comparison, has specialized cells that perform
different functions and are dependent on each other.
• For example some cells procure food, others transport materials, and yet
others enable movement.
•
117
Evolutionary Links
•
•
•
•
•
The evolutionary links between unicellular and multicellular organisms
were may have been colonial forms in which unicellular forms joined
together to form federations of independent cells.
The gradual transition from colonies to multicellular organisms involved
cells becoming increasingly more interdependent as divisions of labor
evolved.
Individual cells in multicellular organisms are specialized to perform
many functions including reproduction, feeding, waste disposal, gas
exchange, and protec-tion, among others.
Multicellularity may have evolved many times among ancestral protists,
leading to new waves of biological diversification and species that are
found today.
Seaweeds, plants, fungi, and animals are all descendents of protists on
a much younger Earth.
118
Words and Terms to Know
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Algae
Amoeba
Apicomplexans
Archaea
Bacteria
Bacterial shapes
Biogenesis
Bioremediation
Chemical cycling
Ciliates
Convergent evolution
Cyanobacteria
Decomposers
Diatoms
Dinoflagellates
Endospores••••••••••••••
Endotoxins and exotoxins
• Exotoxins
• Extremophiles
• Eukaryotic cells
• Flagella
• Forams
• Four-stage hypothesis
• Lyme disease
• Metabolic evolution
• Microorganisms
• Plankton
• Prokaryotic cells•
• Protists
• Protozoans
• Slime molds
• Spontaneous generation
•
119
Miller’s Laboratory Apparatus
http://upload.wikimedia.org
120