Transcript Kingdom Prokaryotae (Monera)

PROKARYOTES
(Domains: Bacteria and Archaea)
Prokaryotes
 They are not Plants, included because:
 Tradition
 Comparative studies: e.g. photosynthesis
 Cause diseases to plants
 Provide insecticides (G.E.), antibiotics
 Present everywhere therefore influence plants
(ecology)
Characteristics of Prokaryotes
 The
first organisms to inhabit earth (3.5 BYA)
 Have nucleoid with a single circular DNA*
 May have plasmid (accessory rings of DNA)
 No histones (DNA is naked)
Structure of the Prokaryotic cell
 Unicellular
 Small cell 1 - 10 µm
 Some lack cell wall (pleomorphic)
Cell wall gives bacteria its shape*
 Lack cell organelles
 Many bacteria (no cyanobacteria) have flagella
Prokaryotes: Reproduction
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Asexual reproduction by binary fission (no mitosis)
Sexual reproduction does not occur but genetic material
can be exchanged by:
Conjugation: transfer of genes between compatible
individuals*
Transformation: incorporation and replication of DNA
pieces from dead or alive prokaryotes
Transduction: incorporation of DNA pieces by means of
bacteriophage
Prokaryotes mutate faster than eukaryotes. Why?
Conjugation in Bacteria
http://www.mpimg-berlindahlem.mpg.de/~ag_lanka/Bacterial_Conjugation.html
http://www.mpimg-berlindahlem.mpg.de/~ag_lanka/Bacterial_Conjugation.html
Prokaryotes: Nutrition
Autotrophic prokaryotes
 Produce their own food
 1- Photoautrophs: use sun E. to reduce CO2 into sugar
Green sulfur bacteria: CO2 + 2H2S  sugar + 2S
Cyanobacteria: CO2+ H2O  sugar + O2
Important as primary producers
Prokaryotes: Nutrition
Autotrophic prokaryotes
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2- Chemoautotrophs:
aerobic, oxidize inorganic
compounds e.g., NH4 to obtain energy:
 Nitrifying bacteria: NH4  NO2  NO3
 The first step carried by Nitrosococcus &
Nitrosomonas
 The second step by Nitrobacter
 important in N2 cycle
Prokaryotes: Nutrition
Heterotrophic prokaryotes
 Cannot make their food
Chemoheterotrophs: aerobic, decomposers
Symbiotic chemoheterotrophs: live in association
with other living organisms as in
Rhizobium/legume’s root association
• Rhizobium: fix atmospheric nitrogen into
ammonia*
• Roots provide carbohydrates to Rhizobium
Rhizobium possesses
the enzyme nitrogenase
that breaks down
atmospheric (N2) into a
form usable by plants
(NH4)
The Need for O2
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Anaerobes:
 Obligate anaerobes: cannot grow in the presence of
O2
 Facultative anaerobes: grow in the presence or
absence of O2 (most bacteria)
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Aerobes: require oxygen
Classification of Prokaryotes
 Bacteria have very little anatomy and virtually no
morphology
 Traditional classified on
 Metabolism (nutrition)
 Wall chemistry
 Ability to carry photosynthesis
 Sensitivity to O2
 Presence of endospores
 For many years Prokaryotes are classified as one
Kingdom, Monera, with 2 divisions: Bacteria and
Cyanobacteria
Recent Classifications
 Recent
classifications based on Ribosomal RNA
 This type of classification reflects phylogenetic
relationships
 rRNA is chosen because of its involvement in
protein synthesis and
 Changes in rRNA sequence occur slowly over
time
Recent Classifications
Domain Bacteria
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Bacteria: the most common type of
Prokaryotes
Cyanobacteria
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Photosynthetic Cyanobacteria:
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Cyanobacteria have phycobilin & Chl(a), lack chl(b)
Have photosystem I & II, liberate oxygen*
Live in a variety of habitats including Antarctica
Very old, enrich environment with O2 (Stromatolites)*
Marine Cyanobacteria form Planktons
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Examples of Cyanobacteria
Cyanobacteria: primary producers in freshwater, soil, & moist habitats
Early organisms that introduced O2 into our atmosphere
Stromatolites
Stromatolites (2.7BYA)
Cyanobacteria’s mucus bind sand & CaCo3
Nitrogen Fixing Cyanobacteria
 Nitrogen
fixation occurs within the
heterocyst*
 The heterocyst contains nitrogenase enzyme
that breaks N3 into ammonia
Heterocyst
Cyanobacteria such as Nostoc & Anabaena possess a
heterocyst where nitrogen fixation takes place
Purple & Green Bacteria
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These are Photosynthetic, anaerobic
 Do not have Chlorophyll
 have baceriochlorophyll, carotenoid
 PS1 present, PSII lacking
 Electron flow is cyclic, (no O2, no ADPH+H)
 Use S (instead of water) to reduce CO2
 CO2 + 2H2S (Light) = (CH2O)n + H2O + 2S
Prochlorophytes
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Possess Chl a, b, & carotenoid, lack phycobilin
 When Prochloron was discovered, it arose
tremendous interest because:
 Resembles chloroplasts
 Exist as obligate symbiont inside marine
invertebrates
Other Important Bacteria
 Nitrogen
fixing bacteria
 Free-living bacteria (Azotobacter, Derxia)
 Nitrifying bacteria
 Denitrifying bacteria
 Symbiotic ( Rhizobium, Agrobacteria)
Domain Archaea
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Differ from bacteria in
Their base sequences of mRNA
Cell wall lack muramic acid
Their membranes have unusual lipid, not affected by drugs
that inhibit ribosomes and protein synthesis
Their metabolism is exotic, thrive in unusual habitats
Evolutionary origin?
Evolved from bacteria (their unusual habitat acts as a
selective pressure)
Their origin is ancient (began when earth is quite different:
reduced atmosphere, acid pools, hot volcanic habitats)
Archaea & Eukarya
 Archaea and Eukarya share:
The same ribosomal proteins
have histone proteins associated with
their DNA as we do
Initiate transcription in the same manner
Have similar types of tRNA
Therefore Eukarya are more closely related to Archaea
than Bacteria
Types of Archaea
 Most Archaea are chemoautotrophs.
 Highly adapted to live in unusual habitats
 Methanogens: Live in anaerobic habitats: swamps & marches
-The only organisms capable of metabolizing CH4 from H2 & CO2.
 Halophiles: Require high salt for growth.
– Common in areas such as the great salt lake and dead sea.
 Thermoacidophiles: Live in acidic hot environment e.g., hot
springs & around volcanoes.
– Their plasma membrane contain unusual lipid that allow them to
function at high temperature
– They reduce sulfide into acidic sulfate