Microbio 310 1st Edition Lecture 19 Outline of Last LectureI. 15.6 Enzymes as Industrial ProductsII. 15.9 BiofuelsIII. 15.10 Expressing Mammalian Genes in BacteriaIV. 15.11Production of Genetically Engineered SomatotropinV. 15.12 Human proteins from microbesVI. 15.16 Genetic Engineering of AnimalsVII. 15.17 Gene Therapy in HumansVIII. 15.18 Transgenic Plants in Agriculture Outline of Current Lecture I. 16.1 Formation and Early History of Earth II. 16.2 Origin of Cellular Life III. 16.3 Microbial Diversification: Consequences for Earth’s Biosphere IV. 16.4 Endosymbiotic Origin of Eukaryotes V. 16.5 The Evolutionary Process VI. 16.6 Evolutionary Analysis: Theoretical Aspects VII. 16.7 Evolutionary Analysis: Analytical Methods Current Lecture16.1 Formation and Early History of Earth• The Earth is ~4.5 billion years oldThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• First evidence for microbial life can be found in rocks ~3.86 billion years old• Stromatolites– Fossilized microbial mats consisting of layers of filamentous prokaryotes and trapped sediment– Found in rocks 3.5 billion years old or younger16.2 Origin of Cellular Life• Early Earth was anoxic and much hotter than present day• Surface origin hypothesis– First self-replicating cells arose out of primordial soup rich in organic and inorganic compounds in ponds on Earth’s surface– Dramatic temperature fluctuations and mixing from meteor impacts, dust clouds, and storms argue against this hypothesis- Subsurface origin hypothesis– Life originated at hydrothermal springs on ocean floor• Conditions would have been more stable• Steady and abundant supply of energy (e.g., H2 and H2S) may have been available at these sites• Prebiotic chemistry of early Earth set stage for self-replicating systems• First self-replicating systems may have been RNA-based (RNA world theory: RNA came before DNA)– RNA can bind small molecules (e.g., ATP, other nucleotides)– RNA has catalytic activity; may have catalyzed its own synthesis• As early Earth was anoxic, energy-generating metabolism of primitive cells was exclusively anaerobic and likely chemolithotrophic (autotrophic)– Obtained carbon from CO2– Obtained energy from H2; likely generated by H2S reacting with H2S or UV light• Early forms of chemolithotrophic metabolism would have supported production of large amounts of organic compounds• Organic material provided an abundant, diverse, and continually renewed source of reduced organic carbon, stimulating evolution of various chemoorganotrophic metabolisms16.3 Microbial Diversification• Molecular evidence suggests ancestors of Bacteria and Archaea diverged ~4 billion years ago• As lineages diverged, distinct metabolisms developed• Development of oxygenic photosynthesis dramatically changed course of evolution• ~2.7 billion years ago, cyanobacteria developed a photosystem that could use H2O instead of H2S, generating O2 (oxygenated the planet)• By 2.4 billion years ago, O2 concentrations raised to 1 part per million; initiation of the Great Oxidation Event• O2 could not accumulate until it reacted with abundant reduced materials in the oceans (e.g., FeS, FeS2)– Banded iron formations: laminated sedimentary rocks formed in deposits of iron- and silica-rich materials; layers of iron oxides interspersed with layers containing iron silicatesand other silica materials; the iron oxides contain iron in the ferric (Fe3+) form produced from ferrous iron (Fe2+) primarily by the oxygen released by cyanobacterial photosynthesis. – prominent feature in geological record• Development of oxic atmosphere led to evolution of new metabolic pathways that yielded more energy than anaerobic metabolisms• Consequence of O2 for the evolution of life– Formation of ozone layer that provides a barrier against UV radiation (natural sunblock)• Without this ozone shield, life would only have continued beneath ocean surface and in protected terrestrial environments16.4 Endosymbiotic Origin of Eukaryotes• Endosymbiosis– Well-supported hypothesis for origin of eukaryotic cells– Contends that mitochondria and chloroplasts arose from symbiotic association of prokaryotes within another type of cell• Both hypotheses suggest eukaryotic cell is chimeric (cell made up of genes from both Bacteriaand Archaea) • This is supported by several lines of evidence:– Eukaryotes have similar lipids and energy metabolisms to Bacteria– Eukaryotes have transcription and translational machinery most similar to Archaea– Antibiotics– Double membrane with proteoglycan inner– Mitochondrial Ribosomes are prokaryotic– Mitochondrial DNA16.5 The Evolutionary Process• Mutations– Changes in the nucleotide sequence of an organism’s genome (sources of variation)– Occur because of errors in replication, UV radiation, and other factors– Adaptative mutations improve fitness of an organism, increasing its survivalo Ex: Bacteria grown under anoxic dark conditions quickly select for non-phototrophic mutants that outcompete and grow faster than cells still making bacteriochlorophyll and carotenoids• Other genetic changes include gene duplication, horizontal gene transfer, and gene loss16.6 Evolutionary Analysis: Theoretical Aspects• Phylogeny– Evolutionary history of a group of organisms– Inferred indirectly from nucleotide sequence data• Molecular clocks (chronometers)– Certain genes and proteins that are measures of evolutionary change– Used to estimate the time of divergence of closely and distantly related organisms– Major assumptions of this approach are that nucleotide changes occur at a constant rate, are generally neutral, and are random• The most widely used molecular clocks are small subunit ribosomal RNA (SSU rRNA) genes– Found in all domains of life• 16S rRNA in prokaryotes and 18S rRNA in eukaryotes– Functionally constant– Sufficiently conserved (change slowly) – Sufficient length (want large target area)16.7 Evolutionary Analysis: Analytical Methods• Comparative rRNA sequencing is a routine procedure that involves the following:– Amplification of the gene encoding SSU rRNA– Sequencing of the amplified gene– Analysis of sequence in reference to other sequences• The first step in sequence analysis involves aligning the sequence of interest with