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Lesson Overview
Viruses
Lesson Overview
20.2 Prokaryotes
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Lesson Overview
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THINK ABOUT IT
When the microscope was first invented, we
humans had just such a shock. Far from being
alone, we share every corner of our world with
microorganisms. Even a seemingly clean
toothbrush contains a film of bacteria on its bristles!
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Classifying Prokaryotes
The smallest & most
abundant microorganisms
on Earth are prokaryotes
unicellular organisms
lack a nucleus.
Prokaryotes have DNA, like
all other cells,
DNA is not found in a
membrane-bound nuclear
envelope
Ex.) E Coli
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Classifying Prokaryotes
Prokaryote DNA is located
in the cytoplasm.
A bacterium such as E. coli
has the basic structure
typical of most prokaryotes.
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Classifying Prokaryotes
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Biologists divided prokaryotes into 2 distinct groups:
Bacteria
Archaea
These groups are very different from each other;
biologists now consider these group of prokaryotes as a
separate domain.
Eukaryotes are the third domain. (have a nucleus)
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Bacteria
The larger of the two domains of
prokaryotes is the Bacteria.
Bacteria include a wide range of
organisms
* lifestyles = different that
biologists do not agree exactly
how many phyla are needed to
classify this group.
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Bacteria
Habitat: Bacteria live
almost everywhere—in
fresh water, in salt water,
on land, and on and within
the bodies of humans and
other eukaryotes.
Escherichia coli, a typical
bacterium that lives in
human intestines, is
shown.
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Bacteria
Bacteria cell wall that
protects the cell from injury
and determines its shape.
The cell walls of bacteria
contain peptidoglycan—a
polymer of sugars and
amino acids that
surrounds the cell
membrane.
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Bacteria
Some bacteria, such as E.
coli, have a second
membrane outside the
peptidoglycan wall that
makes the cell especially
resistant to damage.
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Bacteria
In addition, some
prokaryotes have flagella
that they use for
movement, or pili, which
in E. coli serve mainly to
anchor the bacterium to a
surface or to other
bacteria.
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Archaea
Under a microscope, archaea look very similar to
bacteria.
The walls of archaea lack peptidoglycan
and their membranes contain different lipids.
The DNA sequences of key archaea genes are more
like those of eukaryotes than those of bacteria.
Based on these observations, scientists have
concluded that archaea and eukaryotes are related
more closely to each other than to bacteria.
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Archaea
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Many archaea live in extremely harsh
environments.
One group of archaea produce methane gas and
live in environments with little or no oxygen,
thick mud
digestive tracts of animals.
Other archaea live in extremely salty
environments
Utah’s Great Salt Lake
hot springs
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Size, Shape, and Movement
Size from 1 to 5 micrometers (much smaller than
most eukaryotic cells.)
Shapes
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Rod-shaped-bacilli.
Spherical-cocci.
Spiral and corkscrew-shaped-spirilla.
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Size, Shape, and Movement
Prokaryotes can also be classified by whether they
move and how they move.
Some prokaryotes do not move at all.
Others are propelled by flagella.
Some glide slowly along a layer of slimelike material
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Nutrition and Metabolism
Prokaryotes need a supply of chemical energy, which
they store in the form of fuel molecules -sugars.
Energy is released from these fuel molecules during
cellular respiration, fermentation, or both.
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Nutrition and Metabolism
Prokaryotes vary in the ways they obtain energy and
the ways they release it.
Looking at the two tables on the following slides,
notice that some species are able to change their
method of energy capture or release depending on
the conditions of their environment.
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Nutrition and Metabolism: Energy Capture
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Nutrition and Metabolism: Energy Release
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Growth, Reproduction, and Recombination
binary fission-when growth of a prokaryote
doubled in size, it replicates its DNA and divides in
half, producing two identical cells.
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Growth, Reproduction, and Recombination
Binary fission does not involve the exchange or
recombination of genetic information
asexual reproduction-no genetic exchange
When conditions are favorable, prokaryotes can
grow and divide at astonishing rates—some as
often as once every 20 minutes!
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Growth, Reproduction, and Recombination
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When growth conditions are unfavorable
prokaryotes form an endospore—a thick internal
wall that encloses the DNA and a portion of the
cytoplasm.
Endospores can remain dormant for months or
even years.
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Growth, Reproduction, and Recombination
The ability to form endospores makes it possible for
some prokaryotes to survive very harsh conditions.
The bacterium Bacillus anthracis, which causes the
disease anthrax, is one such bacterium.
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Mutation
Mutations are changes in DNA that occur in organisms.
Mutations are one of the main ways prokaryotes evolve
Inherited by daughter cells produced by binary fission.
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Conjugation
Conjugation is an exchange of genetic information
in bacteria
During conjugation, a hollow bridge forms
between two bacterial cells
genetic material, plasmid, moves from one cell to
the other.
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Conjugation
Many plasmids carry genes that enable bacteria to
survive in new environments or to resist antibiotics
that might otherwise prove fatal.
This type of reproduction increases genetic diversity
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Decomposers
Bacteria called actinomycetes are found in soil &
rotting plant material such as fallen logs,
they decompose complex organic molecules into
simpler molecules.
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Decomposers
By decomposing dead organisms bacteria help to
maintain equilibrium in the environment.
Bacterial decomposers are also essential to
sewage treatment
produce purified water and chemicals
used as fertilizers.
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Producers
Cyanobacteria in the genus Anabaena form
filamentous chains in ponds and other aquatic
environments, where they perform photosynthesis.
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Producers
Photosynthetic prokaryotes are among the most
important producers on the planet.
Food chains everywhere are dependent upon
prokaryotes as producers of food and biomass.
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Nitrogen Fixers
Organisms need nitrogen to make proteins and other molecules.
Some prokaryotes—can convert N2 into useful forms.
The process of nitrogen fixation converts nitrogen gas into
ammonia (NH3).
Ammonia can then be converted to nitrates that plants use, or
attached to amino acids that all organisms use.
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Nitrogen Fixers
Nitrogen-fixing bacteria & archaea provide 90 percent
of the nitrogen
Some plants have symbiotic relationships with
nitrogen-fixing prokaryotes.
The bacterium Rhizobium grows in nodules, or knobs,
on the roots of legume plants such as soybean.
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Nitrogen Fixers
The Rhizobium bacteria within these nodules convert
nitrogen in the air into the nitrogen compounds
essential for plant growth.
The Rhizobium bacteria often live symbiotically within
nodules attached to roots of legumes, such as clover,
where they convert atmospheric nitrogen into a form
that is useable by plants.
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Human Uses of Prokaryotes
Prokaryotes are used in the production of foods &
commercial products.
Yogurt is produced by the bacterium Lactobacillus.
Some bacteria can digest petroleum and remove
human-made waste products and poisons from water.
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Human Uses of Prokaryotes
Other bacteria are used to synthesize drugs &
chemicals through the techniques of genetic
engineering.
Bacteria and archaea adapted to extreme
environments may be a rich source of heat-stable
enzymes can be used in
medicine
food production
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industrial chemistry.