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Chapter 23
 Cellular organisms
 In one of two domains: Archaea
 Generally smaller than eukaryotes
 Most are unicellular, some form colonies or
 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
 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
 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
 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
 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
 In
cytoplasm, not surrounded by a
 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
• 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
 Some
bacterial form dormant, extremely
durable cells in response to unfavorable
environmental conditions
 Tetanus, gas gangrene, anthrax can all
form endospores
 Heterotrophs
– most bacteria obtain
energy from surroundings:
• Chemoheterotrophs – decomposers and pathogens
• Photoheterotrophs – get carbon from other
organisms but have chlorophyll to trap sunlight
 Autotrophs
– manufacture their own organic
• Photoautotrophs – use photosynthesis
• Chemoautotrophs – use chemosynthesis
 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
• Recycle chemical nutrients necessary for life
• Especially important in the nitrogen cycle
• 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