Download Summer Bio153S Lecture 7: prokaryotes

~1.7 billion years of prokaryote dominance
Summer Bio153S Lecture 7:
prokaryotes
earliest
eukaryotes
(1.8 b.y.a.)
Archaean
1400 m.y.
oldest stromatolites
(3.5 b.y.a.)
oldest rocks
Hadean
1900 m.y.
Proterozoic
600
m.y.
Paleozoic era
Mesozoic era
Cenozoic era
origin of earth
(4.5 b.y.a.)
Phanerozoic
prokaryote cell structure is simple
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no cytoskeleton
no membrane-bound organelles
binary fission; no mitosis
DNA in nucleoid (not nucleus)
no chromosomes
permanently haploid
flagellum is simple
distinctive cell walls:
most are single cells
but some form colonies
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may form temporary multicellular forms
- no complex cell junctions
• conjugation: plasmid
or chromosomal DNA
transferred through
pilus
genetic
recombination
separate from
reproduction
prokaryotes are everywhere
• resting spores of Bacillus permians (last
active 250 million years ago) was
“resurrected” in 2000!
• 1 gram of soil has > 10,000 bacterial types
• divide rapidly: under ideal conditions E.
coli could produce mass > earth in 3 d!
• 30 km above Earth’s surface; < 2 km deep
in crust
eukaryotes are metabolically
conservative
1) most are organoheterotrophs
(carbon + energy from
macromolecules)
prokaryotes are metabolically diverse
carbon + energy
1.inorganic
(autotrophs)
2.organic
(heterotrophs)
1. sunlight
(photo)
2. chemicals
(chemo)
i. organic (organo)
ii. inorganic (litho)
prokaryotes:
1) photoautotrophs
2) photoheterotrophs
3) chemoautotrophs
2) plants and some protists are
photoautotrophs
(carbon from CO2; energy from
sunlight)
4) chemoheterotrophs
important in nutrient cycling
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prokaryotes vary in mode of
respiration
5 major groups in Eubacteria:
aerobic: O2 is electron receiver
anaerobic: NO3-, SO42-…
proteobacteria
• most diverse
group
• mostly Gram -ve
• E. coli
• important in N2
fixation
• “purple bacteria”
nitrogen fixation
purple bacteria
• use energy from the sun
but extract electrons from
substances other than
water
• photosynthesis does not
release oxygen
• most species are strict
anaerobes
some proteobacteria are human
pathogens
• e.g. Rhizobium:
symbiosis with legumes
Helicobacter pylori
• makes nitrogen bioavailable
ulcers
Yersinia pestis
bubonic plague
Salmonella
food poisoning
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spirochetes
• Gram-negative bacteria
• difficult to culture
• long, thin, helical and
motile
• axial filaments
• Treponema - syphilis
• Borellia – Lyme disease
firmicutes
• mostly Gram +ve
• e.g. Streptomyces: source of
antibiotics (Streptomycin,
Neomycin and Chloramphenicol)
• some form endospores (tetanus)
chlamydias
• obligate intracellular parasites
• extremely tiny
• human pathogen: STD’s, trachoma
cyanobacteria
• aquatic and
photosynthetic
• contain
chlorophyll a
• photosynthetic
lamellae
(thylakoids)
called “blue-green algae”
• The Red Sea: occasional blooms of
Oscillatoria
• flamingos: pink from eating
Spirulina
stromatolites
• reef-like structures
• cyanobacteria and other
prokaryotes in mineral
matrix
• mucilaginous mats of
bacteria!
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• range from
the Early
Archean (3.5
BYA) to recent
• thrive in
hypersaline
water
early cyanobacteria changed the
atmosphere
• chemically splitting water:
2 H2O ⇒ 4 H+ + O2 + 4e• electrons reduced CO2 to form
organic compounds
• released O2 into atmosphere
prokaryotes:
• can exploit many env’ts
• many substrates and end-products
• can form self-contained communities
• reactions with atmospheric gases
allowed for evolution of eukaryotes
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