CAMPBELL & REECE
CHAPTER 27

typical prokaryote:
 0.5 -5 microns
 unicellular
 variety of shapes
▪ cocci (spherical)
▪ bacilli (rods)
▪ spirochetes (corkscrews)

nearly all have cell wall
 maintains shape
 protects cell
 plasmolyze in hypertonic solution
▪ water loss inhibits cell division hence
salt used as food preservative (ham)
PROKARYOTES

bacterial cell walls
contain
peptidoglycan: a
polymer made of
sugars crosslinked with short
polypeptides
EUKARYOTES

cell walls mostly
cellulose or chitin
ARCHAEA
 (-) peptidoglycan
 (+) variety
polysaccharides &
proteins


used to classify many bacteria as
gram + or gram –
+ or – staining due to differences in
cell wall composition
GRAM +


simpler cell walls
more
peptidoglycan
GRAM 


more complex
less peptidoglycan
+ outer membrane
with
lipopolysaccharides
GRAM +
GRAM -
GRAM + RODS
GRAM - RODS
GRAM +
GRAM -
some strains
virulent
 some drug
resistance (staph)


many strains
virulent:
 tends to be:
 toxic (fever,
shock more
likely)
 drug resistance


works by inhibiting peptidoglycan
cross-linking  makes cell
nonfunctional
since none in eukaryotic cells 
does not harm them

Which infection would more likely
respond to treatment with pcn?


dense, well-defined outermost layer
(called slime layer if not welldefined)
Sticky
 stick to each other in a colony or to
infected individual’s cells

make it more difficult for immune
system to get to bacterial cell


used to stick to host cells
shorter & more numerous than pili


appendages that pull cells together
prior to DNA transfer between cells
aka sex pili


taxis: a directed movement toward
or away from a stimulus
chemotaxis: movement toward a
chemical (+ chemotaxis) or away
from a toxic chemical (- chemotaxis)

most common structure used for
prokaryotic motility



not covered by extension of plasma
membrane as in eukaryotic cell
flagellum
smaller (~ 1/10th width of
eukaryotic flagella)
Bacteria & Archaea flagella similar
in size & rotation mechanism but
composed of different proteins


all these differences suggest
flagella arose independently in all 3
Domains
so are analogous structures not
homologous structures
ARCHAEA
BACTERIA
3 main parts:
1. motor
2. hook
3. filament




evidence indicates it started as a
simpler structure that has been
modified in steps over time
(like evolution of eye) each step
would have had to have been useful
analysis shows only ~1/2 proteins
in flagellum necessary for it to
function



analysis shows only ~1/2 proteins
in flagellum necessary for it to
function
19 of 21 proteins in flagella are
modified versions of proteins that
perform other tasks in bacteria
this is example of exaption:
process in which existing
structures take on new functions
through descent with modification




most have less DNA than
eukaryotic cell
circular chromosome with many
fewer proteins
loop located in nucleoid
most also have a plasmid: smaller
ring(s) of independently replicating
DNA

So how do some prokaryotic cells
undergo photosynthesis and
cellular respiration if they do not
have membrane-bound organelles?
1.
BINARY FISSION


many bacteria can divide in 1- 3
hrs. (some in 20 min)
factors that slow down
reproduction:
1. loss of nutrients
2. toxic metabolic waste
3. competition with other bacteria
4. eaten by predators
1.



Halobacterium
rod-shaped
Archaea
lives in 4M saline (or higher)


developed by certain bacteria to
withstand harsh conditions
resistant cells develop when
essential nutrients lacking


survive boiling water
remain dormant & viable for
centuries




short generations (up to 20,000 in
8 yrs)
adapt rapidly
populations have high genetic
diversity
have been around for 3.5 billion yrs
Factors that promote genetic
diversity:
1. rapid reproduction
2. mutation
3. genetic recombination


because generations are so short
even 1 mutation will produce many
offspring and so increase genetic
diversity which contributes to
evolution


the combining of DNA from 2
sources
occurs 3 ways in prokaryotes
1. transformation
2. transduction
3. conjugation


uptake of foreign DNA from its
surroundings
many bacteria have cell-surface
proteins that recognize DNA from
closely related species & transport
it into the cell

bacteriophages (phages) carry
prokaryotic genes from 1 host cell
to another…..usually as result of
“accidents” during replicative cycle




DNA is transferred between 2
prokaryotic cells (usually same
species) that are temporarily joined
by a mating bridge (from pilus)
transfer in 1 direction only
must have particular piece of DNA:
F factor
DNA transferred either plasmid or
section of loop DNA




phototrophs: obtain energy from
light
chemotrophs: obtain energy from
chemicals
autotrophs: need CO2 as carbon
source
heterotrophs: require at least 1
organic nutrient to make other
organic compounds



obligate aerobes: must use O2 for
cellular respiration
obligate anaerobes: O2 is toxic to
them (fermentation)
faculative anaerobes: use O2 when
available but also carry out
fermentation if have to


N essential to make a.a. & nucleic
acids
Nitrogen Fixation
 cyanobacterium & some methanogens
 N2 from atmosphere  NH3  used by
plants
1.
2.
3.
heterocysts formation
biofilms
sulfate/methane consuming
bacteria


Anabaena, a cyanobacterium
carries genes for both
photosynthesis and N fixation but
any one cell can only do one or the
other at same time
Anabaena forms filamentous
chains, most carry out
photosynthesis but a few,
heterocysts only do N fixation


heterocysts surrounded by
thickened cell wall to prevent O2
from getting in (O2 turns off
enzymes for N fixation)
intercellular connections allow
heterocyst to send fixed N to
neighboring cells
surface-coating colonies of
different prokaryotic species
 channels in biofilm allow nutrients
to reach cells in interior (& wastes
to leave)
 cells secrete
1. signaling molecules  recruit
nearby cells
2. polysaccharides & proteins that
stick cells together



1 archaea species that is a methane
consumer forms ball-shaoed
aggreagate with 1 sulfate
consuming bacteria on ocean floor:
1 uses wastes of other to obtain
necessary nutrients

b/4 technology made molecular
systematics available prokaryotic
organisms grouped by:
 nutrition
 shape
 motility
 Gram stain


began comparing prokaryotic genes
in the 1970’s
concluded some prokaryotes more
closely related to eukaryotes than
to rest of bacteria…..Bacteria &
Archaea Domains

http://www.sumanasinc.com/webcontent/ani
mations/content/pcr.html

used in 1980’s to make multiple
copies of genes from prokaryotes in
soil & water:
handful of soil could have up to
10,000 species of prokaryotes (overall
there are only 7,800 with scientific
names)

BACTERIA
ARCHAEA
EUKARYA
PEPTIDOGLYCAN IN
CELL WALL
+
-
-
MEMBRANE LIPIDS
unbranched
hydrocarbons
RNA
polymerase
Introns in genes
initiator a.a. for
protein synthesis
1 kind
very rare
formylmethionine
some branched unbranched
hydrocarbons hydrocarbons
several
kinds
in some genes
methionine
several
kinds
in many genes
methionine


share some traits with Bacteria,
some with Eukarya
some unique traits too
1.extreme halophiles
 live in highly saline environments
 some tolerate high salinity
 some require high salinity
 proteins function best in extremely
salty environments (die if salinity <9%)
(ocean is 3.5%)
2. extreme thermophiles
 thrive in hot environments
 Sulfolobus live in sulfur-rich
volcanic springs up to 90ºC
 strain-121 lives in deep-sea
hydrothermal vents up to 121ºC
 Most cells would die: DNA would
unfold, proteins would unwind; these
cells have adaptations that avoid this.
3. methanogens
 live in moderate environments
 swamps, marshes
 under ice in Greenland
 in bovine colon, in termites


use carbon dioxide to oxidize H2
gas  produces energy & methane
as a waste product
strict anaerobes

new clades continue to be found


majority of prokaryotic species
have diverse nutritional &
metabolic capabilities




a large & diverse clade
Gram (-)
(+) for photoautotrophs,
chemoautotrophs, & heterotrophs
some aerobic, some anaerobic




all parasites
Intracellular
Gram(-) but lack peptidoglycan in
cell wall
Chlamydia trachomatis: #1 cause
of blindness in the world & causes
most common STD in USA



helical heterotrophs
internal flagellum-like structures
that allows them to corkscrew
through their environment
pathogenic strains:
 Treponema pallidum: syphilis
 Borrelia burgdorferi: Lyme disease
SYPHILIS
LYME DISEASE




photoautotrophic
likely have common ancestor with
chloroplast
solitary or filamentous (some filaments
have cells specialized for N fixation)
component of freshwater or marine
phytoplankton
ACTINOMYCES
fungus-like
form branched
chains
 includes TB and
leprosy
 includes many
decomposers in soil
(earthy odor in soil)


ACTINOMYCES
ODONTOLYTICUS
Mycoplasmas only
bacteria known to
lack cell walls
 smallest known
cells (diameters 0.1
micron)
 some free-living soil
bacteria, some
pathogens


Mycoplasma
pneumoniae
Decomposers
1.

recycle nutrients from dead organisms &
waste products
2. Autotrophic bacteria convert CO2 
organic cpds; some releasing O2
others (kingdom Crenarchaeota) fix N2
gas  organic cpds
3.




Symbiotic Relationships
Mutualism
Commensalism
Parasitism
Pathogens

usually cause illness by producing:
1. exotoxin
2. endotoxin
EXOTOXINS
ENDOTOXINS
released by
pathogen
 cause illness even if
bacteria no longer
present
 example:
Clostridium
botulinum


lippolysaccharide
from outer
membrane of gram
(-) bacteria
 released when
bacteria die
 example: Salmonella
typhi
carry resistant genes
horizontal gene transfer
1.
2.

harmless bacteria  virulent strains


E coli strain 0157:H7 has become a global
threat: causes severe bloody diarrhea
1,387 genes in this strain not originally
from E coli …many are phage genes
 1 of those genes codes for an adhesive
fimbriae that allow bacteria to attach self to
intestinal wall cells & extract nutrients
long history: making cheese, wine, sewage
treatment
new biotechnologies:
 transgenic grains, rice
 bacteria used in manufacture of plastics
 biodegradable
 ethanol- producing bacteria
 bioremediation:
 bacteria that can degrade oil spills

with genetic engineering bacteria
can produce:
 Vitamins
 Antibiotics
 Hormones
 Enzymes