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O R 1 0 0 T R I L L I O N F R I E N D S T H A T
Y O U D I D N ’ T K N O W Y O U H A D
PROKARYOTES
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Prokaryotes
Or 100 Trillion Friends That You Didn’t Know You Had
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The Human Microbiome We are actually a giant ecosystem of microbes
Prokaryotes comprise between 1-3% of the mass of a human body
- up to 6lbs of a 200 lb person can be microbes
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Classification: Some Old, Some New
Biologists have typically classified living things into 5 large groups called kingdoms
- Monera, Protista, Fungi, Plantae & Animalia
Then biologists discovered organisms called Archea – they are prokaryotic organisms but aren’t bacteria.
- What to do?
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The Challenge of Archea Archea present a problem, they a
are prokaryotes
– They have no nucleus or organelles
They also share traits with eukaryotes
- similarities in DNA and synthesis
They have traits unique to themselves
- cell membrane lipids, ability to
survive extremely high temperature
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Enter the Domain System of Classification
Scientists divided living things into 3 Supergroups called domains these consist of Bacteria, Archea and Eukarya
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Archea can be Extremophiles
Some species of archea can be found in environments so extreme, that nothing else lives there- extreme temps, extreme pH, extremely salty etc…
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Bacteria
Earth’s oldest life forms
– between 3.5 and 3.8 billion years old
Most abundant life form – up to 2.5 billion individual bacteria in 1 gram of fertile soil
Very adaptable – found in all of Earth’s
ecosystems
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Bacteria Characteristics
Unicellular
Circular DNA
No organelles
1/10th the size of eukaryotic cells
Flagella-long hair-like structure used for movement
Reproduce asexually –Binary Fission
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Bacterial Shapes
3 main shapes
- coccus – sphere
- bacillus – rods
- spirillum - spiral
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Bacterial Characteristics Metabolic diversity – Bacteria can produce
energy in a variety of circumstances
autotroph – (self-feeding) – some bacteria can produce their own food
- some use photosynthesis – get energy from light
- some use chemosynthesis – get energy from
chemicals
Heterotroph - (other feeding) – many bacteria
are unable to produce their own food and are required to eat other things
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Bacterial Characteristics: Metabolic diversity continued
obligate aerobe – like us these bacteria need oxygen
obligate anaerobe - these bacteria need to be in an oxygen free environment – human gut
facultative anaerobe – these bacteria can live in either an oxygen or oxygen free environment
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Bacterial Structure
Cell Wall
Cell Membrane
Pilus
chromosome
plasmid
flagellum
nucleoid
ribosome
cytoplasm
capsule
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Bacterial Structure: Cell Wall Made of peptidoglycan – a combination of protein and
polysaccharides
Some bacteria called Gram negative bacteria have an additional layer of membrane that contains lipopolysaccharide
- this extra layer inhibits the uptake of antibiotics – protecting
the bacteria
cell membrane
cell wall
cell membrane
Outer membrane
lipopolysaccharide
cell wall
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Gram + vs. Gram -
Absorb stain appear purple
Don’t absorb stain appear pink
The type of cell wall is used by doctors to help diagnose disease
The bacteria are stained with a special stain called Gram stain
Bacteria without the extra membrane, appear purple. These are Gram positive (Gram +) bacteria
Bacteria with the extra membrane appear pink. These are Gram negative ( Gram -) bacteria
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Bacterial Structure continued Pili – hairlike structures usually found
in Gram neg. bacteria. Help the bacteria stick to surfaces.
Also forms conjugation bridge
Chromosome – a single loop of DNA
that is folded on itself
- controls the cell’s function
Nucleoid – the region of the cytoplasm
where the DNA is found
Plasmid – an accessory loop of DNA – small contains only a few genes - can be responsible for: conjugation, antibiotic resistance, unique metabolic properties – like the ability to use hydrocarbons
Capsule – found outside some bacteria stores nutrients and protects the bacteria from changing environmental conditions
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Reproduction - Binary Fission
Bacterial cells undergoing binary fission
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Reproduction - Binary Fission
Asexual reproduction - offspring are genetically identical to parent – no new genetic combinations - under ideal conditions can occur every 20 min - creates large numbers of bacteria in a short time
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Each spot represents
a single bacterial
cell that reproduced
by binary fission to
produce millions of
genetically identical
cells.
Genetically identical,
good or bad?
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Exchanging Genetic Information
Bacterial cells need to be able to exchange genetic information
- creates new genetic combinations which increases the ability of the bacteria to survive
Bacteria have 3 methods for exchanging DNA
-Transduction – viruses carry DNA from one bacterial
cell to another
-Transformation – bacteria can absorb “naked” DNA
released by dead bacteria from the environment
- Conjugation – two bacteria join at a conjugation bridge,
one bacteria passes on a copy of its
plasmid or chromosome
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Exchanging Genetic Information
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Transduction – DNA is carried from one
bacteria to another by a virus
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Transformation: Bacteria absorb “naked” DNA from the
environment
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Conjugation- one cell passes a copy of
its plasmid or chromosome to another
Donor Cell Recipient Cell
A special pilus forms a connection called a conjugation bridge between 2 bacterial cells
Plasmid Conjugation bridge
The donor cell copies its plasmid or chromosome and passes the copy through the conjugation bridge
Cells separate
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Bacteria Play Important Roles in Ecosystems Decomposers
– recycle dead organisms releasing their nutrients back to the environment for use by other organisms – SPONCH
Without decomposers,
the elements on earth
would have remained
locked up in dead organisms and life would have ceased
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Bacterial Roles: Nitrogen Fixation some bacteria contain enzymes which allow them to
convert (or fix) nitrogen from the air into a useable form
- they are nitrogen fixing bacteria
- Why do living things use nitrogen?
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Bacterial Roles: Producers
In some ecosystems
chemosynthetic and
photosynthetic bacteria
serve as the basis of
the food chain
– chemosynthetic bacteria in deep ocean vents
convert hydrogen sulfide (H2S) gas into energy
- cyanobacteria are photosynthetic bacteria
which act as producers in many aquatic
ecosystems
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Bacterial Roles: Symbiotic Bacteria
Many bacteria live in or on other organisms (including humans) and aid their host
- some live in the gut of herbivores helping to
digest cellulose
- bacteria in the gut of humans
aid digestion and produce
vitamins
- bacteria on skin and in body
openings help prevent infection
by harmful organisms
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Bacterial Roles: Pathogenic Bacteria
Pathogens are organisms that cause disease
- only a small portion of bacteria are pathogens
- most bacteria diseases are caused by toxins
released by the bacteria
- these toxins:
- poison cells and damage tissue
- interfere with cell signaling
- over-stimulate cells causing them to malfunction
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Pathogenic Bacteria: Biofilms
Some bacteria can form a biofilm – a matrix made of polysaccharide
- once formed, the matrix traps other bacteria
- the biofilm protects the bacteria, making it hard to kill them
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Antibiotics Antibiotics are chemicals which either kill bacteria or
prevent their growth and reproduction
Bacteria and other microbes produce antibiotics to reduce competition from other organisms
Penicillin was the first to be use to fight disease
- discovered accidently by Alexander Fleming in 1928
Two scientists Walter Florey and Ernst Chain determined
how to use penicillin to
treat disease in 1939.
The discovery of
antibiotics revolutionized
the treatment
of disease
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Antibiotic Action Antibiotics effect bacteria, but not eukaryotic cells
Antibiotics attack bacteria in 5 ways
- some damage the cell walls or prevent new cell wall from forming
- some damage the cell membrane
- some prevent protein synthesis
- some prevent DNA from being copied
- some interfere with bacterial metabolism
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Antibiotic Resistance Some bacteria have developed a resistance to the effect
of some antibiotics
- the number of resistant bacteria is growing
The problem is increased by overuse and misuse of antibiotics
- use of antibiotics to treat viral infections – antibiotics don’t effect
viruses
- the use of antibiotics in livestock (cattle, chickens, pigs)
antibiotics show up in the meat and milk
- people take the antibiotics until they feel better, but stop before all of the bacteria are destroyed
- this kills the most susceptible bacteria, but leaves the more resistant bacteria
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Black Plague-Yersinia pestis
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Syphilis--Treponema pallidum/Bacterial
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Mycobacterium leprae/Bacteria
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Clostridium perfringes/Bacteria
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Vocabulary Microbiome Archea
autotroph pili
heterotroph nucleoid
peptidoglycan capsule
plasmid conjugation bridge
Gram - obligate aerobe
Gram + obligate anaerobe
binary fission facultative anaerobe
conjugation nitrogen fixing bacteria
transduction cyanobacteria
transformation pathogens
biofilm
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Prepared by L. Field – Adjunct Biology Professor Edited by D. Leonard – Learning Specialist The Academic Support Center @ Daytona State College http://www.daytonastate.edu/asc/ascsciencehandouts.html
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