bacteria. structure of a bacterium peptidoglycan cell wall cell membrane ribosome pilidna flagellum
TRANSCRIPT
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BACTERIA
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Structure of a Bacterium
Peptidoglycan
Cellwall
Cellmembrane
Ribosome
PiliDNAFlagellum
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Structure of a BacteriumCapsule: some have a sticky gelatinous
capsule around the cell wall (these bacteria are more likely to cause disease)
Cell wall: gives the cell shape; composed of a peptidoglycan (sugar-protein complex)
Plasma membrane: surrounds the cell and regulates what enters and leaves
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Structure of a Bacterium
Pilus: hairlike structures emerging from the cell surface; helps bacteria stick to a surface or exchange DNA between bacterial cells
Flagellum: long, whiplike structure that enables movement
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Structure of a Bacterium
Chromosome: single DNA molecule arranged as a circular chromosome; not enclosed in a nucleus
Plasmid: small circular chromosome piece containing a few genes
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Classifying Bacteria
Bacteria are classified according to:ShapeArrangementGram stain
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Classifying Bacteria
ShapeSpherical - CocciRod - BacilliCorkscrew - Spirillae
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Classifying Bacteria
ArrangementSingularPairs – Diplo Chains – StreptoClusters – Stapylo
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Classifying Bacteria
Gram stainStaining method involving two dyesThe dye absorbed by the bacteria depends
on properties of the cell wallBacteria are either Gram positive or Gram
negativePositive stain bluish-purpleNegative stain reddish-pink
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Prokaryote Cell Wall Structure
peptide sidechains
cell wallpeptidoglycan
plasma membrane
protein
Gram-positive bacteria
Gram-negative bacteria
peptidoglycan
plasmamembrane
outermembrane
outer membrane of lipopolysaccharides
cell wall
peptidoglycan = polysaccharides + amino acid chainslipopolysaccharides = lipids + polysaccharides
That’simportant foryour doctorto know!
Gram-Positive bacteria
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Metabolism
Obligate aerobes – must have oxygen to survive
Obligate anaerobes – cannot live if oxygen is present
Facultative anaerobes- can live either with or without oxygen
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Archaebacteria&
Bacteria
Classification3 Domain system
reflects a greater understanding of evolution & molecular evidenceBacteria: EubacteriaArchae: ArchaebacteriaEukaryotes:
Protists Plants Fungi Animals
Prokaryote
Eukaryote
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Classification of Bacteria
All bacteria are prokaryotesVery simple organismsAll are unicellular In general, they are smaller than
eukaryotesCircular DNA which is not enclosed in a
nucleusLack membrane-bound organelles
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Classification of Bacteria
ArchaebacteriaEubacteria
Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria
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Archaebacteria
a.k.a. Extremophiles Live in oxygen-free environments Obtain energy from sun or inorganic
molecules
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Archaebacteria: Thiobacilli
Heat- and acid-loving bacteria Live in sulfur springs
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Archaebacteria: Thiobacilli
Consume sulfur Combine it with oxygen to produce
energy Produce sulfur dioxide as by-product
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Archaebacteria: Thiobacilli
Sulfur dioxide can combine with water to form sulfuric acid
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Archaebacteria: Halobacteria
Salt-loving bacteria Live in saturated salt water like the
Great Salt Lake
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Archaebacteria: Halobacteria
Produce purple pigments Use purple pigment to carry out
photosynthesis the way plants use chlorophyll
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Archaebacteria: Alkalophytes
Live in aquatic environments with high pH
Forms the food basis upon which thousands of large organisms are dependent
Lake Nakuru
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Archaebacteria: Methane Bacteria
Cannot live in the presence of oxygen Live in stomachs of cows and sewage
treatment ponds
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Archaebacteria: Methane Bacteria
Obtain energy from CO2 and hydrogen gas
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Archaebacteria: Deep Subsurface Bacteria
Live in rocks beneath Earth’s surface (as deep as 3,000 feet)
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Archaebacteria: Deep Subsurface Bacteria
Obtain energy from H+ produced from reaction between minerals in rock and groundwater seeping in
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Classification of Bacteria
ArchaebacteriaEubacteria
Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria
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Heterotrophic Eubacteria
Obtain food from other living organismsparasites
Obtain food from dead organisms or organic wasteRecycle nutrients in decomposing organic
material
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Classification of Bacteria
ArchaebacteriaEubacteria
Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria
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Autotrophic Eubacteria
Obtain energy from lightPerform photosynthesis
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Autotrophic Eubacteria
CyanobacteriaMost contain blue-green pigment (but some
are red or yellow)Form chains: not unicellular
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Classification of Bacteria
ArchaebacteriaEubacteria
Heterotrophic eubacteriaAutotrophic eubacteriaChemosynthetic eubacteria
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Chemosynthetic Eubacteria
Obtain energy from breakdown of inorganic substances (S and N compounds)
Key for agriculture:Convert atmospheric N to a form plants can
use
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Reproduction in Bacteria
Can reproduce rapidly (every 20 minutes)
Luckily, most run out of nutrients and water before the colony gets very large
Most reproduce by binary fissionBacterium copies its chromosomeOld chromosome and copy attach to the
plasma membrane at opposite endsCell grows and becomes larger
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Reproduction in Bacteria
Most reproduce by binary fissionGrowth causes two chromosomes to
separatePartition forms and separates the cell into
twoEach new cell has one copy of the original
chromosomeCreates two cells genetically identical to one
another
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Genetic Exchange in Bacteria
ConjugationSexual form of bacterial reproductionOne bacterium passes all or part of its
chromosome to another cellTransfer occurs across piliCreates two bacteria genetically different
from one anotherThey then reproduce by binary fission
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Transduction: Transfer of genes from one bacterium to another by a bacteriophage.
Ex. Toxin gene in Corynebacterium diphtheriae
Genetic Exchange in Bacteria
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Transformation: Taking in DNA from the outside environment.
Ex. Rough Streptococcus pneumoniae transformed into smooth S. pneumoniae. Bacterial species in biofilm communities.
Genetic Exchange in Bacteria
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Survival
If conditions become less than ideal some bacteria can form endospores
Tough outer covering resistant to:Drying outTemperature extremes (boiling water)Harsh chemicals
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Survival
Closturidium botulinumProduces a deadly toxinEndospores can withstand boiling
temperaturesCanned foods must be pressure cooked to
kill the endospores
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Six week old infant with botulism, which is evident as a marked loss of muscle tone, especially in the region of the head and neck.
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Survival
Closturidium tetaniObligate anaerobe that produces a deadly
neurotoxinEndospores are found on nearly every
surface on the planetWhen endospores get into a moist,
oxygen-free environment (such as inside a puncture wound) they germinate
Reason for getting a tetanus shot
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Tetanus
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Survival
Bacillus anthracisAka. AnthraxEndospores live in soilWhen inhaled they germinate
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Decomposers
Break down dead organisms and recycle the nutrients that make them
Without decomposition we would run out of the molecules necessary for life
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Nitrogen-fixation
Plants and animals need nitrogen to make protein
The atmosphere is mostly nitrogen but plants and animals can’t use it
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Nitrogen-fixation
Nitrogen-fixing bacteria convert nitrogen in the atmosphere into nitrogen plants can take up with their roots
Animals get their nitrogen by eating plants
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Biotechnology
Production of foods like butter, cheese, and yogurt
Cleaning up oil spillsSynthesizing drugs and chemicals
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Digestion
Much of what we eat would pass through our bodies without being digested if we didn’t have bacteria in our digestive tracts
They break down plant matter and synthesize vitamins for us
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Bacterial Diseases
Bacteria cause illness one of two ways:Breaking down host cells or tissues for foodNormal metabolic processes generate
toxins
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Bacterial Diseases
Most food-borne illnesses are caused by bacteria:E. coli comes from infected, undercooked
beefSalmonella comes from infected,
undercooked poultry (meat and eggs)Botulinum causes botulism – a deadly form
of food poisoning
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Controlling Bacteria
Antibiotics are drugs that kill bacteria (NOT VIRUSES)
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Controlling Bacteria
Most bacteria like warm, moist, dark conditions
Exposing them to other conditions kills them or slows reproduction
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Controlling Bacteria
Examples: Cooking foods makes it too hot for most
bacteria to surviveRefrigerating or freezing foods makes it too
cold for them to reproduceDrying foods makes it impossible for
bacteria to reproducePickling causes bacterial cells to burst