Earth History When did life begin? What was the first form of life? When did the first eukaryotes appear? MinuteEarth: The Story of our Planet Figures\Chapter22\High-Res\life7e-tab-22-01-1.jpg Bio@Tech Campbell & Reece, Fig. 26.10 1 1 1
What role did oxygen play in evolution? great oxygenation event Bio@Tech 2 2 2
“Tree of Life” Bacteria Eukarya Archaea 4 Symbiosis of chloroplast ancestor with ancestor of green plants 3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes 2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells 1 Last common ancestor of all living things 4 3 2 1 Billion years ago Origin of life According to this tree, which group, Bacteria or Archaea, are more closely related to eukaryotes? Bio@Tech Campbell & Reece, Fig. 25.18 3 3 3
How do Bacteria and Archaea differ? unique cell wall structures unique cell membrane lipids DNA replication, transcription & translation machinery similar to eukaryotes
Microfossils Cyanobacteria (Nostocales) from the Bitter Springs Chert, Central Oz, 850 Ma (J.W. Schopf, UCLA http://www.cushmanfoundation.orgt/slides/stromato.html) 2.5-2.7 Ga microfossils (Schopf, 2006. Phil. Trans. R. Soc. B 361: 869-885) 5 5 5 5
Stromatolites Stromatolite fossils are structurally indistinguishable from living examples Campbell & Reece, Fig. 26.11 6 6 6
Microbes in the Biosphere From Whitman et al. 1998 PNAS 95:6578-6583: 4 x 1030 prokaryotic cells on Earth Subsurface ~3.8 x 1030 Aquatic ~1 x 1029 Soils ~2.5 x 1029 Animals (termites) ~5 x 1024 Air ~ 5 x 1019 350-550 Pg* C = 60-100% of C in plants 30-50% of C in biosphere 90% of organic N, P in biosphere *Pg = petagram = 1015 grams Bio@Tech 7 7
Microbes R Us 70 x 1012 prokaryotic cells per person Mostly in gut: colon has 300 x 109/g Approx. 30% of solid matter in feces Gut microbiome > 100 x human genome Human microbiome project Bio@Tech 8 8
Microbes are planetary engineers Invented all metabolism Catabolism Anabolism Depleted ocean of dissolved iron (Fe2+) Anoxygenic photosynthesis 4 Fe2+ + CO2 + 4 H+ 4 Fe3+ + CH2O + H2O Oxygenic photosynthesis H2O + CO2 + CH2O + O2 4 Fe2+ + O2 + 4 H+ 4 Fe3+ + 2 H2O And injected oxygen into atmosphere! Bio@Tech 9 9
Banded iron formed by iron oxide precipitates (Image courtesy of Dr. Pamela Gore, Georgia Perimeter College) (Hayes, 2002, Nature 417: 127-128) 10 10 10
oxidation/reduction reactions power cells Higher-energy molecules are oxidized (lose electrons) Lower-energy molecules are reduced (gain electrons) G = -nFE (kJ/mol) n = # e- transferred F = Faraday constant E = redox potential difference 11 11
Respiration: electrons from NADH charge a membrane pH gradient H+ electrochemical gradient H+ Electron transport chain cell membrane NADH O2 or other terminal electron acceptors such as NO3-, SO42-, Fe3+, etc. NAD+ See also: http://www.microbelibrary.org/images/Tterry/anim/ETSbact.html H+ 2e- Electron donors (CH2O and other organic carbon food molecules) 12 12
NAD+/NADH is the cell’s main electron (hydrogen) carrier NAD = nicotinamide adenine dinucleotide. NADH + H+ +1/2 O2 ↔ NAD+ + H2O ΔGo = -52.4 kcal/mol. 13 13 13
Terminal Electron Acceptors Microbes can use different terminal electron acceptors, but prefer oxygen because it givies the highest energy yield. O2 ∆G = -479 kJ mol-1 NO3- ∆G = -453 kJ mol-1 Mn4+ ∆G = -349 kJ mol-1 Fe3+ ∆G = -114 kJ mol-1 SO42- ∆G = -77 kJ mol-1 14 14 14
Oxidative phosphorylation: F1 ATPase video Periplasmic space Oxidative phosphorylation: F1 ATPase video H+ Stator Rotor http://www.youtube.com/watch?v=PjdPTY1wHdQ stored energy in proton gradient (proton motive force) powers ATP synthesis; analogous to a dam powering a water turbine Internal rod Cata- lytic knob See also: http://www.microbelibrary.org/images/Tterry/anim/ATPsynthbact.html ADP + P ATP i Cytoplasm 15 15 15
Extraction of electrons from carbohydrates to reduce NAD+ H+ electrochemical gradient ETC ADP ATP NADH NADH NADH + FADH2 ATP Pyruvate oxidation Glycolysis Citric acid cycle NAD+ CO2 NAD+ FAD CO2 ADP Glucose, NAD+, ADP 16 16
A soil-based microbial fuel cell Bio@Tech 17 17