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

Carl Woese and George Fox

rRNA Zuckerkandl and Pauling Emile Zuckerkandl ( ); Austria & USA. Molecular biology and molecular clock Linus Carl Pauling ( ) 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 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 DNA molecule Translation Polypeptide Gene 1 Gene 2 Gene 3 DNA strand Transcription RNA Codon Amino acid

Ribosomal Function A typical prokaryotic cell may 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 Using 24 genes and 3000 taxa

Gram Stain and Structure

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)

Archaea Differ from the Eubacteria –Form of ribosomes –No murein –Different lipids –Different RNA polymerase