The Great Tree of Life
! "As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications." -- Charles Darwin, 1859
Origins ! Origins - How did life arise? ! “But if (and Oh! What a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity etc. …” Darwin, Letter to J. Hooker, 1871
1 “Prokaryotes” Organisms that run the world ! Dominant Life forms on Earth "10x the biomass of Eukaryotes "Extreme metabolic diversity "The basis for eukaryotic metabolism
“Prokaryotes” Organisms that run the world ! Dominant Life forms on Earth "10x the biomass of Eukaryotes "Extreme metabolic diversity "The basis for eukaryotic metabolism ! Crucial for many global processes "Biogeochemical cycling "It’s a prokaryotic world. We need them, but they don’t need us!
2 “Prokaryotes” vs. Eukaryotes (Briefly) ! Unlike Eukaryotes, prokaryotes have "No nuclear envelope "No membrane bound organelles "Circular DNA, with relatively few genes
“Prokaryotes” - Classification ! Formerly all prokaryotes lumped together
3 “Prokaryotes” - Classification ! Formerly all prokaryotes lumped together "Primitive similarities "“Prokaryotes” now considered to be __phyletic #United by primitive similarities ! Three domains of life
Prokaryotes - Two Domains Bacteria Archaea Eukarya Organelles, nucleus Linear chromosomes Mitosis and meiosis
LUCA(C) DNA/Proteins RNA, ribosomes Circular Chromosome RNA world?
Abiogenesis
4 Swapping Genes Lateral (= Horizontal) Gene Transfer ! Unlike most Eukaryotes, “prokaryotes” can laterally transfer genes!!! "Very important for evolution ! Various mechanisms "E.g. transformation, transduction, conjugation. Know general phenomenon, not details
The very early history of life
5 The very early history of life
The very early history of life ! Earth forms about 4.5 bya ! Life appears “quickly”! ! Environment very different "Volcanoes "Meteor impacts "Very little oxygen ! Glycolysis a widespread and primitive pathway - Implies …?
6 Photosynthesis Energy from the sun! ! Use light as an energy source for making ATP (Light reaction)
"O2 as a by-product (usually)
! Use ATP to create sugars from CO2 ! These are now photoautotrophs ! The oxygen revolution: "2.5 billion years ago "Good news, bad news
The oxygen revolution: Good news, bad news ! Origin of cyanobacteria "Increased Oxygen levels (eventually) "Oxygen is very reactive - breaks bonds "Bad news for anaerobic organisms
! But, allowed the evolution of aerobic respiration!
7 Aerobic Respiration ! Much greater yield of ATP ! In some ways, the opposite of Photosynthesis "Photosynthesis:
#ATP (from Light rxn) +CO2-> Sugar+O2 "Aerobic respiration:
#Sugar+O2 -> ATP + CO2
Big Idea: Evolution is a tinkerer ! 1) Pathways for production of ATP in aerobic respiration apparently borrowed from (or at least shared with) photosynthesis! ! 2) Anaerobic origins of photosynthesis apparent even in modern plants "Enzymes used for fixing CO2 are interfered with by O2 - photorespiration "Photorespiration as an “evolutionary relic”
8 Summary ! “Prokaryotes” oldest, most diverse group "All combinations of energy, carbon sources ! Early Earth environment anaerobic "Only anaerobic glycolysis possible - low yield "Very widespread, apparently old ! Photosynthesis -> Oxygen revolution 2.5bya "Bad for anaerobes (major extinction!) "Allowed aerobic respiration!!! ! Big Idea: Evolution as tinkering
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