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Prokaryotes
Chapter 27
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Prevalence of Prokaryotes
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Prokaryotes are the oldest, abundant for
over 2 billion years before the appearance of
eukaryotes
structurally simplest,
most abundant forms of life on earth.
– 5,000 different kinds currently recognized
bacillus
coccus
spirillum
pili - hairlike structures - attachment
endospores - resistant to environment
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Prevalence of Prokaryotes
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Prokaryotes versus Eukaryotes
– unicellularity
– cell size
– chromosomes
– cell division and recombination
– internal compartmentalization
– flagella
– metabolic diversity
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Prokaryotic Diversity
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Very early, prokaryotes split into two lines
– Archaea and bacteria are as different in structure and
metabolism from each other as either is from eukarya.
Comparing archaebacteria and bacteria
– plasma membranes
composed of different lipids
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cell wall archaebacteria lack peptidoglycan
gene translation machinery archaebacteria similar to
eukaryotes
gene architecture bacteria not interrupted by introns
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Gram Stain for Bacterial classification
Gram-positive - thicker peptidoglycan
Gram-negative - thinner peptidoglycan
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Flagellar Motor
flagella – slender protein - locomotion
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The Cell Interior
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Internal membranes
– invaginated plasma membrane
Nucleoid region
– lack nucleus - genes encoded with single
double-stranded DNA
Ribosomes
– Prokaryotic ribosomes are smaller than
eukaryotic ribosomes, and differ in protein
and RNA content.
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Prokaryotic Variation
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Two process create bacterial variation:
– mutation
 spontaneous errors in DNA replication
 prokaryotic ability to mutate rapidly
– genetic recombination
 occurs by gene transfer from one cell to
another by viruses or conjugation
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Prokaryotic Metabolism
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Autotrophs
– obtain carbon from inorganic CO2
 photoautotrophs - sunlight
 chemoautotrophs - inorganic chemicals
Heterotrophs
– obtain carbon from organic molecules
 photoheterotrophs - sunlight
 chemoheterotrophs - organic molecules
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Benefits of Prokaryotes
decomposition
nitrogen fixation
digestive tract of animals
nonpolluting insect control
pollutant removal
commercial production of antibiotics
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