THE PROKARYOTES. Systematics of Prokaryotes Focus on animals and plants –History limited to 20% of evolutionary time How to classify prokaryotes? Limited.

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