Unformatted text preview: or can be highly chemically dis?nct from the exterior environment two diﬀerent hypothesis on this early world Günter Wächtershäuser: 1st catalysis by pyrite (iron disulﬁde) and not proteins or RNA? ‘nucleic acid replicator ﬁrst’ seems plausible except: primordial soup experiments have never produced RNA polymers DNA is not cataly1c RNA probably came before DNA evidence: RNA is capable of forming many complex structures and cataly?c ac?vi?es • protein synthesis is carried about by RNA structures (ribosomes) • retroviruses can synthesize DNA copies of RNA molecules by reverse transcrip?on hMp://www.darwinthenandnow.com/2010/06/rna‐world/ the early Earth ?meline 4.6 bya ‐ solar system began forming pre‐life earth: hot, most water was in the atmosphere as vapor (a lot was lost to space), lots of UV radia?on reaching surface later, Earth cooled, liquid water from comet impacts was able to persist on surface [these impacts also brought N2 and heat energy; note that Mars is thought to have had a similar early history] ~ 3.5 ‐ 4 bya ‐ life on Earth begins hMp://www.cosmographica.com/gallery/
poroolio2007/content/297_EarlyEarth_large.html Earliest fossils Stromatolites ‐ structures formed by cyanobacteria‐like organisms •
• • Evolu?on of Earth’s ancient ecosystem Marine photosynthe?c bacteria dominated the earth for 1‐2 billion years Before this ?me ‐ no oxygen in atmosphere Massive produc?on of oxygen for a very long ?me – Oxygenated the oceans – Oxidized most of the iron on Earth (now mined as iron ore) – Then, increased percentage of oxygen in atmosphere Enabled the evolu?on of organisms with respiratory metabolism Current composi1on of Earth’s atmosphere hMp://en.wikipedia.org/wiki/Earth's_atmosphere#Composi?on Eukaryotes appear in the fossil record 2.3 billion years aTer prokaryotes The 3 domains of life •
• Bacteria Prokaryotes Archaea Eukarya (Eukaryotes) All three have in common: – Glycolysis hMp://en.wikipedia.org/wiki/Glycolysis –
– DNA replica?on mechanism Transcrip?on, transla?on, gene?c code Plasma membranes Ribosomes Diﬀerences between Prokaryotes and Eukaryotes • Prokaryotes do not have cytoskeleton • Prokaryotes do not divide by mitosis – They use binary ﬁssion • Prokaryotes do not have a nucleus • DNA is usually circular • Prokaryotes do not have membrane‐enclosed organelles (mitochondria, chloroplasts, Golgi apparatus) – But they can have infoldings of the plasma membrane for various func?ons • For diﬀerences between two domains of Prokaryotes, see table 26.1 – Don’t have to memorize these When did Prokaryotes originate? • First fossils – 3.5 billion years ago (bya) • First fossil evidence of cellular life – But there was already signiﬁcant diversity • Billions of years to adapt and diversify before Eukaryotes appeared >3 bya >2 bya Prokaryote success • Es...
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- Spring '08
- Biology, HMP, • Spiral movement, – Gas vesicles, asexual •