Georgia Tech School of Biology Bio@Tech Earth History When did life begin? What was the first form...

Georgia Tech School of Biology

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Earth HistoryWhen did life begin?

What was the first form of life?

When did the first eukaryotes appear?

MinuteEarth: The Story of our Planet

Campbell & Reece, Fig. 26.10


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What role did oxygen play in evolution?

great oxygenation event


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“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

1

2

3

4

0

Billio

n years ag

o

Origin of life


According to this tree, which group, Bacteria or Archaea, are more closely related to eukaryotes?


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)


Stromatolites

• Stromatolite fossils are structurally indistinguishable from living examples



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Microbes in the BiosphereFrom 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 biosphere90% of organic N, P in biosphere

*Pg = petagram = 1015 grams


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

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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


Banded iron formed by iron oxide precipitates

(Image courtesy of Dr. Pamela Gore,Georgia Perimeter College)(Hayes, 2002, Nature 417: 127-128)


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


Respiration: electrons from NADHcharge a membrane pH gradient

NADH

Electron donors (CH2O and other organic carbon food molecules)

O2 or other terminal electronacceptors such as NO3

-, SO42-,

Fe3+, etc.

H+ electrochemical gradient

Electron transport chain

NAD+

cell membrane

H+

See also:http://www.microbelibrary.org/images/Tterry/anim/ETSbact.htmlH+ 2e-


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.


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


Oxidative phosphorylation:F1 ATPase video

Periplasmic space

Rotor

H+

Stator

Internalrod

Cata-lyticknob

ADP+P ATP

i

Cytoplasm

stored energy in proton gradient (proton motive force) powers ATP synthesis;analogous to a dam powering a water turbine

See also:http://www.microbelibrary.org/images/Tterry/anim/ATPsynthbact.html

http://www.youtube.com/watch?v=PjdPTY1wHdQ


Extraction of electrons from carbohydrates to reduce NAD+

Glycolysis Citric acid cycle

NADH

Glucose, NAD+, ADP

H+ electrochemical gradient

Pyruvate oxidation

ETC

ATPATP NADH + FADH2NADH

ADP

CO2 CO2NAD+ ADPNAD+FAD


A soil-based microbial fuel cell

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Georgia Tech School of Biology Bio@Tech Earth History When did life begin? What was the first form...

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