the prokaryotes. systematics of prokaryotes focus on animals and plants –history limited to 20% of...
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THE PROKARYOTES
Systematics of Prokaryotes• 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
Carl Woese and George Fox
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
Why should rRNA be conserved?
• 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
• 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
Ribosomal Function
A typical prokaryotic cellmay have
10,000+ ribosomes
Where does rRNA enter the picture?
Ribosomal Structure
Two subunits
Ribosomal subunits=rRNA molecules + proteins
Prokaryotes Eukaryotes
What’s the ‘S’?
• Svedberg units: a measure of how quickly particles sediment in an ultracentrifuge
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
Why then does 5S + 23S = 50S?
Why then does 5S + 23S = 50S?
Shape AND size determine sedimentation rate…
Ribosomal RNA Molecules
• Components of the ribosomes of ALL ORGANISMS
• Changes in rRNA nucleotide sequence indicative of evolutionary history
SSU rRNA
A modification of Woese from Brock et al. (1994).
Two different supertrees generated by ML methods for complete genomes of 45 taxa. Daubin et al. 2002
Ciniglia et al. 2004
Lang et al. 2013Using 24 genes and 3000 taxa
Gram Stain and Structure
Eubacteria
>9 KingdomsSame type of ribosomesPolysaccharide of outer wall made of MureinMost groups involved in global nutrient cyclingMany of economic importanceDiseaseOther functions (e.g. antibiotic producers)
Archaea
• Differ from the Eubacteria– Form of ribosomes– No murein– Different lipids– Different RNA polymerase