As late as 1977, all prokaryotes were put into one single kingdom called Monera. Taxonomists no longer
accept that concept. Some
prokaryotes are more closely
related to eukaryotes than other
prokaryotes. Most taxonomists
now accept the concept of super
kingdoms or domains. Two of the
three domains are prokaryotes.
General information
I. Three common shapes (cocci,
bacilli, spirilla)
II. Small 0.5-5 m
III. Bacterial cell wall made of
carbohydrate polymers that are
connected by polypeptide chains
(peptidoglycan). Gram-positive
bacteria (stain purple with Gramstain) have cell walls with just the
peptidoglycan wall connected to
plasma membrane. Gramnegative bacteria (stain pink) have
peptidoglycan wall sandwiched
between two membranes. The cell wall of Archae is made from polysaccharides and certain proteins but
NOT peptidoglycans.
Some prokaryotes have a second layer outside the cell wall.
-Capsule-sticky layer of carbohydrates or proteins.
-Fimbriae-protein appendages that allows the prokaryote to
attach to surfaces
IV. Nucleoid region-area where circular DNA
chromosome is located. Chromosome lacks
histones (some prokaryotes in Archae do).
May also contain smaller circular pieces of
DNA or plasmids.
V. Ribosomes are smaller than cytoplasmic
eukaryotic ribosomes.
VI. Some prokaryotes have infoldings of the
plasma membrane similar to cristae and
some photosynthetic prokaryotes have
internal membranes similar to thylakoid
membranes.
VII. Some prokaryotic cells have flagella.
The flagellum is different from eukaryotic
cells. It is a solid core of protein (1/10th width). It is driven by a system of rings in the cell wall. ATP
pumps transports H+ out cell. When the H+ diffuse back in it powers the flagella which rotates like a
helicopter rotor. Flagellated prokaryotes can exhibit taxis moving toward or away chemicals, nutrients or
oxygen.
Reproduction-Asexual
reproduction is via binary
fissionBacteria can obtain
genetic variation via
conjugation,
transformation, or
transduction
Conjugation-(Lederberg &
Tatum)
1. ConjugationCertain bacteria that have been mutated would need additional nutrients in their media in
order to grow. Bacteria without these mutations will grow on minimal media. E.Coli had been mutated
and 2 different strains were found
#1- needed methionine and vitamin biotin but could make its own leucine and threonine.
#2-needed threonine and leucine but could not make its own methionine and vitamin biotin. When these
two types were mixed, there emerged some new cells that had the ability to grow on minimal media.
Conclusion: There had to be some exchange of genes or recombination of genes.
Recombination has occurred because the new cells can grow on minimal media. It was also discovered
that in addition to the main chromosome, prokaryotic cells contained smaller circles of DNA (plasmids)
which also contained genes.
Plasmids replicate independent of the main
chromosome. These plasmids are being
replicated.
In order for conjugation to occur there must be 2
different mating types F+ (male) and F- (female).
F+ males have a plasmid (sex factor) which is
replicated. When a F+ and F- meet, they form a
cytoplasmic bridge or pilus. The copied F+
plasmid is transferred to F- making it F+.
The population never completely is converted to
F+ because
1. F- can undergo bacterial reproduction (fission) faster than F+ can conjugate.
2. The formation of the pilus, allows for certain viruses to attack, and they only attack F+ cells.
Some F+ plasmids are inserted into the main chromosome becoming Hfr (high frequency recombinants).
When Hfr conjugates with F-, the entire main chromosome is replicated.
However during transfer only part of the chromosome is transferred.
The gene for Hfr is usually at the end of the chromosome, so that the receiving cell F- will stay an F-. The
longer the pilus stays together, the more genes transferred.
Autono
mous
plasmid
sPlasmid
s that
never
integrate
themsel
ves into
the
chromos
ome.
They
may
carry
genes
that
include antibiotic resistance or a virulence factor. Plasmids have the ability to
replicate themselves so that a prokaryotic cell may have 1,000 to 3,000 copies of it.
2. Transformation- Involves prokaryotic cells taking up extraneous DNA from the
environment. Genetic engineering uses this technique in transforming bacteria and
using engineered plasmids.
3.Transduction- Bacterial cells obtaining DNA via a viral vector.
The rapid reproduction, mutations, and genetic recombination allows for a great
variety in their metabolic pathways.
-Photoautotroph-does photosynthesis and uses CO 2 as its carbon source
-Chemoautotroph-uses CO2 and use chemicals like H2S and NH3 for energy instead of light
-Photoheterotroph-uses light for energy but obtains carbon from an organic source.
-Chemoheterotroph-uses organic compounds for both an energy source and carbon source. Most are
decomposers or pathogens that break organic compounds down.
Types of cell respiration
-Obligate aerobes must use oxygen for cell respiration or will die without it
-Obligate anaerobe- oxygen is not used for cell respiration and the cell is actually poisoned by it.
-Facultative anaerobes-can use oxygen when present or do fermentation if oxygen is not present.
Nitrogen fixation
Some prokaryotes have the ability to “fix” atmospheric nitrogen (N 2) into ammonia NH3. Then the
ammonia can be converted into nitrates and nitrites. The nitrogen compounds then can be converted into
amino acids. Important part of nitrogen cycle. Some prokaryotes live in symbiotic relationships with this
pathway. The root nodules of legumes contain nitrogen fixing bacteria.
Types of photosynthesis-Some prokaryotes are photosynthetic. There are two types of photosynthesis in
prokaryotes
Type I that gives off O2 as a by product.
Contains photosystem I and II like higher plants
Contains chlorophyll a like higher plants
Splits water
6 CO2 + 6 H2O -> C6H12O6 + 6 O2Type II that does not give off O2 as a by product.
Contains only photosystem I
Contains bacteriochlorophyll
Splits hydrogen sulfide
CO2 + 2H2S -> (CH2O)n + 2 S
Domain Bacteria-Supergroups
1. Proteobacteria-Gram negative with 5 subgroups. Metabolic diverse- photoautotrophs,
chemoautotrophs, and heterotrophs. Some are aerobic while others are anaerobes.
2. Chlamydias-Obligate parasites only live in other cells. Major cause of blindness.
3. Spirochetes-Spiraled shaped with internal like flagellum. Caused syphilis and Lyme disease.
4. Cyanobacteria-does type I photosynthesis generating oxygen. Some cells specialized (heterocysts) for
fixing nitrogen
5. Gram-positive bacteria-Metabolic diverse group. Some obligate parasites, some secrete antibiotics.
Domain Archaea-Supergroups can live in extreme environments and more normal environments. More
closely related to eukaryotes than other prokaryote
1.Extreme halophiles can tolerates saline environments. Tolerance from slightly saline to over 9% saline
(Ocean is 3.5% saline).
2.Exterme thermophiles can tolerate very hot environments. Proteins are very stable at this temperature
and DNA remains as a double helix. One strand of Geogemma barossi can tolerate temperature of over
121o C.
3. Methanogens- use CO2 to oxidize H2 to make methane gas. Obligate anaerobes. Found under ice,
swamps, guts of cattle, and termites.
4. Moderate environment-many prokaryotes from the Domain Archaea are live in moderate environments.
in the environment
Symbiotic relationshipsMutualistic- Ex-certain bacteria in your gut are important to the digestive system and the bacteria
benefit by the food that is provided to them.
Commensalistic-Ex There a many bacteria living on the surface of the skin. They do not harm or
provide any benefit to the epidermal cells. The epidermal cells provide oils, food and a habitat to
live
Parasitic-Ex-Some prokaryotes are pathogens (cause disease). Many bacterial diseases can be
treated with antibiotics which are compounds that destroy prokaryotic cells but not eukaryotic
cells. Usually the disease is caused by either an exotoxin (made and secreted by the prokaryote)
or endotoxin (made by the prokaryote and only released if the prokaryote dies). Botulism is
caused by an exotoxin made by Clostridium botulinum and typhoid fever is caused by an
endotoxin made by Salmonella typhi. Prokaryotes are the most dominant organisms on this earth.
Without them, life as we know would not exist. They are important in
-decomposers
-nutrient recycling
-nitrogen fixation
-food industry
-symbiosis
-medicine
-producers in food chains.