chapter 23. cellular organisms in one of two domains: archaea and eubacteria generally smaller...
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ProkaryotesChapter 23
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Features of Prokaryotes Cellular organisms In one of two domains: Archaea and Eubacteria Generally smaller than eukaryotes Most are unicellular, some form colonies or
filaments No membrane-enclosed organelles Ribosomes are located in the cytoplasm In some – the inner plasma membrane is
extensively folded inward to provide reaction sites
Most have a cell wall
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Shapes of Prokayrotes Cocci – spherical
• Single cells• Groups of two: diplococci• Long chains: streptococci• Clumps: staphylococci
Bacilli – rod-shaped• In single rods or long chains
Spiral:• Spirochete – flexible spiral• Spirillum – rigid spiral
Vibrio – spirillum shaped like a comma
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Bacterial Shapes
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Cell Wall Provides shape and stability Allows the cell to inhabit hypotonic
surroundings without bursting Does not help in hypertonic solutions
– most bacteria do not grow well in foods preserved with high sugar or salt content
In eubacteria the cell wall contains peptioglycan
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Gram staining Gram-positive bacteria:
• Appear blue or violet• Cell walls with a very thick layer of peptidoglycan• Disease causing gram-positive bacteria are easily
killed by penicillin which interferes with peptidoglycan production
Gram-negative bacteria:• Appear red or pink• Cell walls have two layers: a thin peptidoglycan
layer and a thick outer membrane
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Other bacterial structures Capsule – a slime layer that surrounds
the cell wall in some species• May provide pathogenic bacteria protection• May also allow some bacteria to attach to
surfaces (e.g.: to cause dental plaque) Pili – short, hair-like projections of
protein which allow bacteria to adhere to each other or other surfaces
Flagella – longer projections found in mobile bacteria
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Bacterial structures
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Prokaryote DNA In cytoplasm, not surrounded by a
membrane In most, a singular circular
chromosome Most bacteria also contain smaller
circular plasmids which may contain genes that code for enzymes, genetic exchange, or antibiotic resistance
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Bacterial DNA
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Bacterial Reproduction Asexual:
• Binary fission – DNA replication followed by a transverse wall separating the two new cells
• Budding – a bulge forms and matures, eventually separating from the original cell
• Fragmentation – walls develop within a single cell which then separates into several different cells
Genetic exchange:• Transformation – fragments of DNA released by one cell
are picked up by another• Transduction – a phage (form of a virus) carries bacterial
DNA from one to another• Conjugation – two different bacterial cells exchange
genetic material
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Bacterial Reproduction
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Endospore Formation Some bacterial form dormant,
extremely durable cells in response to unfavorable environmental conditions
Tetanus, gas gangrene, anthrax can all form endospores
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Prokaryotic Metabolism Heterotrophs – most bacteria obtain
energy from surroundings:• Chemoheterotrophs – decomposers and
pathogens• Photoheterotrophs – get carbon from other
organisms but have chlorophyll to trap sunlight energy
Autotrophs – manufacture their own organic molecules• Photoautotrophs – use photosynthesis• Chemoautotrophs – use chemosynthesis
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Prokaryote Classification Archaea:
• No peptidoglycan in cell walls• Many live in extremely harsh environments:
no oxygen, high salt, or high temperatures Eubacteria:
• Peptidoglycan in cell walls• Widely distributed and better known
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Ecological Significance Decomposers
• Recycle chemical nutrients necessary for life• Especially important in the nitrogen cycle
Pathogens• Exotoxins - poisons produced by the bacteria that cause the
damage• Endotoxins – components of the cell walls that affect the
host only when released from the dead bacteria Food production
• Microbial fermentation – yogurt, pickles, olives, sauerkraut, vinegar, soy sauce
Antibiotic production Genetic engineering Bioremediation