1. 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 jpg
Campbell & Reece, Fig 1 1 1

2. What role did oxygen play in evolution?
great oxygenation event 2 2 2

3. “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?
Campbell & Reece, Fig 3 3 3

4. How do Bacteria and Archaea differ?
unique cell wall structures
unique cell membrane lipids
DNA replication, transcription & translation machinery similar to eukaryotes

5. Microfossils
Cyanobacteria (Nostocales) from the Bitter Springs Chert, Central Oz, 850 Ma (J.W. Schopf, UCLA
Ga microfossils (Schopf, Phil. Trans. R. Soc. B 361: ) 5 5 5 5

6. Stromatolites
Stromatolite fossils are structurally indistinguishable from living examples
Campbell & Reece, Fig 6 6 6

7. Microbes in the Biosphere
From Whitman et al PNAS 95: :
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
Pg* C = % of C in plants
30-50% of C in biosphere
90% of organic N, P in biosphere
*Pg = petagram = 1015 grams 7 7

8. 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 8 8

9. 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 Fe H2O
And injected oxygen into atmosphere! 9 9

10. Banded iron formed by iron oxide precipitates
(Image courtesy of Dr. Pamela Gore, Georgia Perimeter College)
(Hayes, 2002, Nature 417: ) 10 10 10

11. oxidation/reduction reactions power cells
Higher-energy molecules are oxidized (lose electrons)
Lower-energy molecules are reduced (gain electrons)
G = -nFE (kJ/mol)
n = # e- transferred
F = Faraday constant
E = redox potential difference 11 11

12. 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: H+
2e-
Electron donors (CH2O and other organic carbon food molecules) 12 12

13. NAD+/NADH is the cell’s main electron (hydrogen) carrier
NAD = nicotinamide adenine dinucleotide.
NADH + H+ +1/2 O2 ↔ NAD+ + H2O ΔGo = kcal/mol. 13 13 13

14. 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

15. Oxidative phosphorylation: F1 ATPase video
Periplasmic space
Oxidative phosphorylation: F1 ATPase video H+
Stator
Rotor
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:
ADP + P
ATP i
Cytoplasm 15 15 15

16. 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

17. A soil-based microbial fuel cell 17 17