THE PROKARYOTES

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THE PROKARYOTES

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THE PROKARYOTES. Systematics. Focus on animals and plants History limited to 20% of evolutionary time How to classify prokaryotes? Limited in morphological characters. Carl Richard Woese. 1928-2012, USA; Developed system based on 16S rRNA in 1977. Flow of information in a cell…. - PowerPoint PPT Presentation

Transcript of THE PROKARYOTES

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THE PROKARYOTES

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Systematics• Focus on animals and plants

– History limited to 20% of evolutionary time

• How to classify prokaryotes?

Limited in morphological characters

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Carl Richard Woese

1928-2012, USA; Developed system based on 16S rRNA in 1977

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Carl Woese and George Fox

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rRNA

Zuckerkandl and Pauling

Emile Zuckerkandl (1922-2013); Austria & USA. Molecular biology and molecular clock

Linus Carl Pauling (1901-1994) USA Founder of fields like quantum chemistry and molecular biology

Suggested that a tree of life might be generated by comparing sequences of biopolymers like RNA

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Flow of information in a cell…

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• When DNA is transcribed, the result is an RNA molecule

Figure 10.10

DNA molecule

Translation

Polypeptide

Gene 1

Gene 2

Gene 3

DNA strand

Transcription

RNA

Codon

Amino acid

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• When DNA is transcribed, the result is an RNA molecule

• RNA is then translated into a sequence of amino acids

Figure 10.10

DNA molecule

Translation

Polypeptide

Gene 1

Gene 2

Gene 3

DNA strand

Transcription

RNA

Codon

Amino acid

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Ribosomal Function

A typical prokaryotic cellmay have

10,000+ ribosomes

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Where does rRNA enter the picture?

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Ribosomal Structure

Two subunits

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Ribosomal subunits=rRNA molecules + proteins

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Prokaryotes Eukaryotes

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What’s the ‘S’?

• Svedberg units: a measure of how quickly particles sediment in an ultracentrifuge

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What’s the ‘S’?• Svedberg units: a measure of how

quickly particles sediment in an ultracentrifuge

• Larger the particle, the greater its S value

• Smaller subunit of a ribosome sinks slower than the larger subunit

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Why then does 5S + 23S = 50S?

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Why then does 5S + 23S = 50S?

Shape AND size determine sedimentation rate…

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Ribosomal RNA Molecules• Components of the ribosomes of ALL

ORGANISMS

• Changes in nucleotide sequence indicative of evolutionary history

• “highly conserved molecules”…

What does this mean?

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Ribosomal Function

• PROTEIN SYNTHESIS

• Not much room for error!

• Disruption of ribosome structure likely to disrupt protein synthesis…

Life threatening!

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Practical applications…• Some antibiotics (e.g. erythromycin and

streptomycin) work by targeting the 70S ribosomes

• Alter shape and prevent bacteria from synthesizing proteins needed to survive

• Why are our own ribosomes not affected by the same drugs???

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A modification of Woese from Brock et al. (1994).

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Two different supertrees generated by ML methods for complete genomes of 45 taxa. Daubin et al. 2002

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Ciniglia et al. 2004

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Lang et al. 2013Using 24 genes and 3000 taxa

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Gram Stain and Structure

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Eubacteria

• >9 Kingdoms• Same type of ribosomes• Polysaccharide of outer

wall made of murein• Most groups involved in

global nutrient cycling• Many of economic

importance• Disease• Other functions (e.g.

antibiotic producers)

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Proteobacteria

• Disparate functional groups joined by molecular sequences

• Likely the source of mitochondria

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Alphaproteobacteria• Rikettsias (typhus Rocky

Mtn spotted fever

• Rhizobias (N-fixing bacteria)

• Likely the ancestor of mitochondria was from this group

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Gammaproteobacteria• Usually small rods or

cocci• Causative agents of

Bubonic Plague, Tuleremia, Legioner’s Disease, Cholera

• Includes Escherichia coli

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Spirochaetae

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Spirochaetae• Spiraled with internal

flagella• Many are free-living• Causative agents of

Lyme disease, syphilis, yaws, and relapsing fever

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Cyanobacteria

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Cyanobacteria• Like free-living chloroplast • Group from which chloroplasts

appeared• Form filaments, colonies• Very large for bacteria• Some produce toxins• Many are nuisance algae in

over-fertilized waters• Source of most atmospheric

oxygen, especially prior to eukaryotes

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Firmicutae• Lack second outer

membrane of Eubacteria

• Gram positive

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Aphragmabacteria• Tiny, smallest

genome of any non-virus

• No walls• Obligate parasites • One causes

pneumonia; many plant pathogens

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Anoxybacteria• Obligate anaerobes

• Causative agents of botulism and tetanus

• Botox

• Common in soil and animal digestive systems

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Endosporobacteria• Produce resistant spores

• Many major human pathogens, including anthrax, staph (including methicillin-resistant Staphylococcus aureus), strep

• Includes Lactobacillus

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Actinobacteria• Many are slow-growing and fungus-

like• Antibiotic sources (e.g.

streptomycin, actinomycin)• Causative agents of leprosy and

tuberculosis; diptheria• Bacteria which cause holes in Swiss

cheese• Bifida, a necessary commensal in

our lower bowel

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Deinococcobacteria• Thermophiles

• Deinococcus withstands 6,000 rads (and up to 1500 megarads)

• Thermus, found at Yellowstone, enzymes used for PCR

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ArchaeaDiffer from the Eubacteria

– Form of ribosomes– No murein– Different lipids– Different RNA polymerase

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Crenarchaea• These are the

hyperthermophiles

• They tend to inhabit very hot environments that are rich in sulfur

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Euryarchaeota• Halobacteria

• Methanobacteria

• Thermoplasmobacteria

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Viruses• Non-cellular• Usually nucleic acid

and protein• Types

– DNA (ss & ds)– RNA (ss & ds)– DNA RT– RNA RT– Prions

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Some Human Viral Diseases• Herpes• Smallpox• Hepatitis (B, C, D)• Yellow Fever• Dengue fever• West Nile• HIV• Ebola• Rabies• Chicken Pox

/Shingles

• Rubella (German Measles)• Influenza• Polio• Mumps• Measles• Epstein-Barr• Hemorrhagic fever• Rota • Rhinovirus• Transmissible spongiform

encephalopathy (TSE)

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Theories on Origin of Viruses• Regressive Hypothesis: cellular parasites of

larger cells that became simplified

• Cellular Origin Hypothesis: pieces of living cells that can replicate (e.g. strands of nucleic acids like plasmids or transposons)

• Coevolution Hypothesis: evolved together with the first cells as their parasites