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Prokaryotes
(Archaea and Bacteria)
Chapter 28
The First Cells
Microfossils are fossilized forms of microscopic life
-Oldest are 3.5 billion years old
-Isotopic analysis and concentration of
carbon-12 in fossils suggests that carbon
fixation was active as much as 3.8 BYA
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The Cyanobacteria
Stromatolites are mats of cyanobacterial cells that
trap mineral deposits
-Oldest are 2.7 billion years old
-Lipids were found in ancient rocks
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Flagella, spin like propellers
Composed of the protein flagellin
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Prokaryotic Features
Metabolic diversity
-Two types of photosynthesis
-Oxygenic = Produces oxygen
-Anoxygenic = Nonoxygen producing
- E.g: Sulfur and sulfate
-Chemolithotrophic prokaryotes derive
energy from inorganic molecules
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Bacteria vs. Archaea
Plasma membrane
-Bacterial-Connected to glycerol by ester linkages
-Archaeal-Connected to glycerol by ether linkages
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Prokaryotic Shapes
Most prokaryotes have one of 3 basic shapes
-Bacillus = Rod-shaped
-Coccus = Spherical
-Spirillum = Helical-shaped
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The Bacterial Cell Wall
Maintains shape and protects the cell from
swelling and rupturing
Consists of peptidoglycan
-Polysaccharides cross-linked with peptides
Cell wall is the basis of the Gram stain
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The Bacterial Cell Wall
Two main types
-Gram-positive bacteria
-Thick peptidoglycan
-Teichoic and lipoteichoic acids
-Gram-negative bacteria
-Thin peptidoglycan
-Have an outer membrane
-Contains lipopolysaccharide
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The Bacterial Cell Wall
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The Bacterial Cell Wall
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Internal Structure
Internal membranes
-Invaginated cell
membrane
-For respiration or
photosynthesis
Endospores
-Highly-resistant structures
-Released upon cell lysis
-Can germinate back to normal cell
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Prokaryotic Genetics
Prokaryotes do not reproduce sexually
However, they undergo horizontal gene
transfer, which is of three types
-Conjugation = Cell-to-cell contact
-Transduction = By bacteriophages
-Transformation = From the environment
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Conjugation
Transfer of the F plasmid occurs through the
conjugation bridge
The end result is two F+ cells
-R (antibiotic resistance) plasmids
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-Virulence plasmids (E. coli O157:H7 strain)
Transduction
Viruses package bacterial DNA
and transfer it in a subsequent infection
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Transformation
Natural transformation
-DNA that is released from a dead cell is
picked up by another live cell...Horizontal
gene transfer (no cell fusion so not sexual17 !!)
Prokaryotic Metabolism
Acquisition of Carbon
-Autotrophs = From inorganic CO2
-Heterotrophs = From organic molecules
Acquisition of Energy
-Chemolithotrophs = From inorganic
chemicals
-Phototrophs = From sunlight
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Prokaryotic Metabolism
Photoautotrophs
-Cyanobacteria
Chemolithoautotrophs
-Nitrifiers
Photoheterotrophs
-Purple and green nonsulfur bacteria
Chemoheterotrophs
-Majority of prokaryotes
-Use organic molecules for C and energy
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Prokaryotic Metabolism
Type III secretion system
-Found in many Gram-negative bacteria
-Used to transfer virulence proteins directly
into host cells
-Yersinia pestis – Bubonic plague
-Pseudomonads – Plant pathogens
-Blights, soft rot, wilts
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Human Bacterial Disease
Tuberculosis
-Mycobacterium tuberculosis
-Afflicts the
respiratory system
-Mutidrug-resistant
(MDR) strains are
very alarming
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Human Bacterial Disease
Dental caries (tooth decay)
-Plaque consists of bacterial biofilms
-Streptococcus ferments sugar to lactic acid
-Tooth enamel degenerates
Peptic ulcers
-Helicobacter pylori is the main cause
-Treated with antibiotics
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Sexually transmitted diseases (STDs)
Gonorrhea
-Neisseria gonorrhoeae
-Can pass from mom to baby via birth canal
-Can cause pelvic inflammatory disease (PID)
Chlamydia
-Chlamydia trachomatis
-Can cause PID and heart disease
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Beneficial Prokaryotes
Prokaryotes are crucial to chemical cycles
-Decomposers release a dead organism’s
atoms to the environment
-Photosynthesizers fix carbon into sugars
-Nitrogen fixers reduce N2 to NH3
(ammonia)
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Beneficial Prokaryotes
Bacteria are used for bioremediation
-Remove pollutants from water, air and soil
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-Exxon Valdez oil spill