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Bacteria
Bacteria Characteristics
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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 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
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 wall
cell membrane
pilus
chromosome
nucleoid
capsule
plasmid cytoplasm
flagellum
ribosome
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 wall
cell
membrane
cell
membrane
lipopolysaccharide
cell wall
Outer membrane
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 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
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 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
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
• 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
Vocabulary
autotroph
heterotroph
peptidoglycan
plasmid
Gram Gram +
binary fission
conjugation
transduction
transformation
biofilm
pili
nucleoid
capsule
conjugation bridge
obligate aerobe
obligate anaerobe
facultative anaerobe
nitrogen fixing bacteria
cyanobacteria
pathogens