georgia tech school of biology bio@tech earth history when did life begin? what was the first form...
Post on 02-Jan-2016
216 Views
Preview:
TRANSCRIPT
Georgia Tech School of Biology
Bio@Tech
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
Georgia Tech School of Biology
Bio@Tech
What role did oxygen play in evolution?
great oxygenation event
Georgia Tech School of Biology
Bio@Tech
“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
Campbell & Reece, Fig. 25.18
According to this tree, which group, Bacteria or Archaea, are more closely related to eukaryotes?
Georgia Tech School of Biology
How do Bacteria and Archaea differ? unique cell wall structures unique cell membrane lipids DNA replication, transcription & translation
machinery similar to eukaryotes
Georgia Tech School of Biology
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)
Georgia Tech School of Biology
Stromatolites
• Stromatolite fossils are structurally indistinguishable from living examples
Campbell & Reece, Fig. 26.11
Georgia Tech School of Biology
Bio@Tech
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
Georgia Tech School of Biology
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
Georgia Tech School of Biology
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
Georgia Tech School of Biology
Banded iron formed by iron oxide precipitates
(Image courtesy of Dr. Pamela Gore,Georgia Perimeter College)(Hayes, 2002, Nature 417: 127-128)
Georgia Tech School of Biology
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
Georgia Tech School of Biology
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-
Georgia Tech School of Biology
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.
Georgia Tech School of Biology
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
Georgia Tech School of Biology
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
Georgia Tech School of Biology
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
top related