Transcript The PROKARYOTES

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Archae and BacteriaThe PROKARYOTES
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 mm
III. Bacterial cell wall made of carbohydrate polymers that are
connected by polypeptide chains (peptidoglycan). Grampositive bacteria (stain purple with Gram-stain) have cell
walls with just the peptidoglycan wall connected to
plasma membrane. Gram-negative bacteria (stain pink)
have peptidoglycan wall sandwiched between two
membranes. The cell wall of Archae are 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.
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Reproduction-Reproduction is via binary fission. Bacteria
can obtain genetic variation via conjugation, transformation, or
transduction
Conjugation-(Lederberg & Tatum)
1. Conjugation-Certain 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.
The arrow points to a plasmid in a lysed E.Coli
cell which is then magnified. This plasmid
contains genes that makes the cell resistant to the
antibiotic tetracycline.
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.
Conjugating bacteria with
the pilli connecting the
cells to one another to
exchange DNA.
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.
Autonomous plasmids-Plasmids that never integrate themselves into
the chromosome. 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 CO2 as its
carbon source
-Chemoautotroph-uses CO2 to make organic compounds on
its own and uses 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 (N2) 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 O2
Type 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 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 (Marine
environments is 3.5% saline).
2. Extreme thermophiles can tolerate very hot environments.
Proteins are very stable at this temperature and DNA
remains as a double helix. One strain 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.
Prokaryotes 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.
This chart compares and
contrast three different
domains. It is based on the
sequencing of the rRNA
found in the small subunit.
The Archae prokaryotes are
more closely related to
eukaryotes than it is to the
Bacteria prokaryotes.