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Ch. 27 Prokaryotes
Domain Bacteria
Domain Archaebacteria
Domain
Bacteria
2007-2008
Domain
Archaea
Common ancestor
Domain
Eukarya
Bacteria live EVERYWHERE!
• Bacteria live in all ecosystems
– on plants & animals
– in plants & animals
– in the soil
– in depths of the oceans
– in extreme cold
– in extreme hot
– in extreme salt
– on the living
– on the dead
Microbes always
find a way to
make a living!
Bacterial diversity
Rods(bacilli) and spheres(cocci) and spirals(helical)…Oh My!
eukaryote cell
Prokaryote Structure
prokaryote
cell
• Unicellular
– bacilli, cocci, spirilli
• Size
– 1/10 size of eukaryote cell
• 1 micron (1um)
• Internal structure
– no internal compartments
• no membrane-bound organelles
• only ribosomes
– circular chromosome, naked DNA
• not wrapped around proteins
mitochondria
Variations in Cell Interior
cyanobacterium
(photosythetic) bacterium
chloroplast
aerobic bacterium
Prokaryote Cell Wall Structure
Gram-positive bacteria
peptide side
chains
cell wall
peptidoglycan
plasma membrane
protein
That’s
peptidoglycan = polysaccharides + amino acid chains
important for
lipopolysaccharides = lipids + polysaccharides
your doctor
to know!
outer membrane of
Gram-negative bacteria
lipopolysaccharides
cell wall
outer
membrane
peptidoglycan
plasma
membrane
Motility
• 1- Flagella
• 2- Helical shape
(spirochetes)
• 3- Slime
• 4-Taxis
(movement away or
toward a
stimulus)
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Form & Function
• Nucleoid region (genophore: noneukaryotic chromosome)
• Plasmids
• Asexual reproduction: binary fission
(not mitosis)
• “Sexual” reproduction (not meiosis):
• transformation~ uptake of genes from
surrounding environment
• conjugation~ direct gene transfer
from 1 prokaryote to another
transduction~ gene transfer by viruses
• Endospore: resistant cells for harsh
conditions (250 million years!)
Genetic variation in bacteria
• Mutations
– bacteria can reproduce every 20 minutes
• binary fission
– error rate in copying DNA
• 1 in every 200 bacteria has a mutation
• you have billions of E. coli in your gut!
– lots of mutation potential!
• Genetic recombination
– bacteria swap genes
• plasmids
– small supplemental
circles of DNA
• conjugation
conjugation
– direct transfer of DNA
Nutrition & Metabolism
• Photoautotrophs: photosynthetic;
harness light to drive the synthesis of
organics (cyanobacteria)
• Chemoautotrophs: oxidation of
inorganics for energy; get carbon from
CO2
• Photoheterotrophs: use light to
generate ATP but get carbon in an
organic form
• Chemoheterotrophs: consume organic
molecules for both energy and carbon
– saprobes- dead organic matter
decomposer
– parasites- absorb nutrients from living
hosts
• Oxygen relationships: obligate aerobes;
facultative anaerobes; obligate
anaerobes
Bacteria as pathogens
– animal diseases
• tooth decay, ulcers
• anthrax, botulism
• plague, leprosy, “flesheating” disease
• STDs: gonorrhea,
chlamydia
• typhoid, cholera
• TB, pneumonia
• lyme disease
plant diseases
• wilts, fruit rot, blights
opportunistic: normal residents of
host; cause illness when defenses are
weakened
•Koch’s postulates: criteria for
bacterial disease confirmation
•exotoxins: bacterial proteins that
can produce disease w/o the
prokaryote present (botulism)
•endotoxins: components of gram membranes (Salmonella)
Bacteria as beneficial (& necessary)
• Life on Earth is dependent on bacteria
– decomposers
• recycling of nutrients from dead to living
– nitrogen fixation
• only organisms that can fix N from atmosphere
– needed for synthesis of proteins & nucleic acids
– plant root nodules
– help in digestion (E. coli)
• digest cellulose for herbivores
– cellulase enzyme
• produce vitamins K & B12 for humans
– produce foods & medicines
• from yogurt to insulin