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Prokaryotes
Or 100 Trillion Friends That You Didn’t Know You Had
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
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?
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
Enter the Domain System of Classification
Scientists divided living things into 3 Supergroups called domains these consist of Bacteria, Archea and Eukarya
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…
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
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
Bacterial Shapes
3 main shapes - coccus – sphere
- bacillus – rods
- spirillum - spiral
Bacterial Characteristics Metabolic diversity – Bacteria can
produce energy in a variety of circumstancesautotroph – (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
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
Bacterial Structure
Cell WallCell Membrane
Pilus
chromosome
plasmid
flagellum
nucleoid
ribosomecytoplasm
capsule
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
cellmembrane
cell wall
cellmembrane
Outer membrane
lipopolysaccharide
cell wall
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 aspecial stain called Gram stain
Bacteria without the extra
membrane, appear purple. These are Gram positive (Gram +) bacteriaBacteria with the extra membrane appear pink. These are Gram negative ( Gram -) bacteria
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
Reproduction - Binary Fission
Bacterial cells undergoing binary fission
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
Each spot represents a single bacterial cell that reproduced by binary fission to produce millions of genetically identical cells.
Genetically identical, good or bad?
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
Exchanging Genetic Information
Transduction – DNA is carried from one bacteria to another by a virus
Transformation: Bacteria absorb “naked” DNA from the
environment
Conjugation
Conjugation- one cell passes a copy of its plasmid or chromosome to another
Donor CellRecipient Cell
A special pilus formsa connection calleda conjugation bridgebetween 2 bacterialcells
Plasmid Conjugation bridge
The donor cell copies its plasmidor chromosome andpasses the copy through the conjugation bridge
Cells separate
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
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?
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
Bacterial Roles: Symbiotic BacteriaMany 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
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
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
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
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
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
Black Plague-Yersinia pestis
Syphilis--Treponema pallidum/Bacterial
Mycobacterium leprae/Bacteria
Clostridium perfringes/Bacteria
VocabularyMicrobiome Archeaautotroph piliheterotroph nucleoidpeptidoglycan capsule plasmid conjugation bridgeGram - obligate aerobeGram + obligate anaerobebinary fission facultative anaerobeconjugation nitrogen fixing bacteriatransduction cyanobacteriatransformation pathogensbiofilm