rRNA 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 Zuckerkandl and Pauling
• When DNA is transcribed, the result is an RNA molecule DNA molecule Gene 1 Gene 2 Gene 3 • RNA is then translated into a sequence of amino acids DNA strand Transcription RNA Translation Codon Polypeptide Amino acid Figure 10.10
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
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???
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)
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
Actinobacteria • Many are slow-growing and funguslike • 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
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