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Prokaryotes
Chapter 28
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The First Cells
Prokaryote Video
Microfossils are fossilized forms of
microscopic life
-Oldest are 3.5 billion years old
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The First Cells
Stromatolites are mats of cyanobacterial
cells that trap mineral deposits
-Oldest are 2.7 billion years old
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The First Cells
Isotopic analysis of carbon-12 in fossils
suggests that carbon fixation was active
as much as 3.8 BYA
Biomarkers are organic molecules of
biological origin
-Lipids were found in ancient rocks
-This indicates that cyanobacteria are
at least 2.7 billion years old
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Prokaryotic Diversity
Prokaryotes are the oldest, and structurally
simplest forms of life
Prokaryotes are ubiquitous
Less than 10% of species are known
Bacteria (also called eubacteria)
Archaea (formerly called archaebacteria)
-Many archaeans are extremophiles
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Prokaryotic Features
Unicellularity
-Most are single-celled
-Some can form complex biofilms
Cell size
-Most are less than 1 mm in diameter
Chromosome
-Single circular double-stranded DNA
-Found in the nucleoid
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Prokaryotic Features
Internal compartmentalization
-No membrane-bounded organelles
Flagella
-Simple in structure; spin like propellers
Cell division
-Most divide by binary fission
Genetic recombination
-Occurs through horizontal gene transfer
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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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Marsh
• Detritus = Organic material
• Bacteria break down detritus through
anaerobic processes creating sulfur
dioxide = rotten egg smell.
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Molecular Classification
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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
Archaea do not possess peptidoglycan
-Some have pseudopeptidoglycan
Cell wall is the basis of the Gram stain
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The Bacterial Cell Wall
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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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External Layers
S-layer
-A rigid paracrystalline layer found in some
bacteria and archaea
-Aids in attachment
Capsule
-A gelatinous layer found in some bacteria
-Aids in attachment
-Protects from the immune system
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Bacterial Appendages
Pili
-Short, hairlike structures
-Found in Gram-negative bacteria
-Aid in attachment and conjugation
Flagella
-Long, helical structures
-Composed of the protein flagellin
-Involved in locomotion
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Bacterial Appendages
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Internal Structure
Nucleoid region
-Contains the single, circular chromosome
-May also contain plasmids
Ribosomes
-Smaller than those of eukaryotes and differ
in protein and RNA content
-Targeted by antibacterial antibiotics
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Mutation
Mutations can arise spontaneously in bacteria
-Also caused by radiation and chemicals
Mutations (and plasmids) can spread rapidly
in a population
-Negative consequences for humans
-For example:
-Methicillin-resistance
Staphylococcus aureus (MRSA)
-Vancomycin-resistant
Staphylococcus aureus (VRSA)
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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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Human Bacterial Disease
In the early 20th century, infectious diseases
killed 20% of children before the age of five
-Sanitation and antibiotics considerably
improved the situation
In recent years, however, many bacterial
diseases have appeared and reappeared
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Human Bacterial Disease
Tuberculosis
-Mycobacterium tuberculosis
-A scourge for
thousands of years
-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
-“Silent STD”
-Can cause PID and heart disease
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Sexually transmitted diseases (STDs)
Syphilis
-Treponema pallidum
-Can pass from mom to baby via birth canal
-Four distinct stages
-Primary - Chancre
-Secondary - Rash
-Tertiary - Latency
-Quaternary - Heart and nerve damage
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Sexually transmitted diseases (STDs)
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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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Bacterial Decomposition in
Wastewater Treatment
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Beneficial Prokaryotes
Prokaryotes may live in symbiotic
relationships with eukaryotes
-Mutualism = Both parties benefit
-Nitrogen-fixing bacteria on plant roots
-Cellulase-producing bacteria in animals
-Commensalism = One organism benefits
and the other is unaffected
-Parasitism = One organism benefits and
the other is harmed
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Beneficial Prokaryotes
Bacteria are used in genetic engineering
- “Biofactories” that produce various
chemicals, including insulin and antibiotics
Bacteria are used for bioremediation
-Remove pollutants from water, air and soil
-Exxon Valdez oil spill
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Beneficial Prokaryotes
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Chapter 29 - Protists
• Protists are the most diverse of the four
eukaryotic kingdoms
– Unicellular, colonial and multicellular groups
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Some are photosynthetic (like plants)
Autotrophic & Heterotrophic
Found anywhere in the water
Video Clip
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