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: http://zebu.uoregon.edu/disted/ph121/l9.html
Дата изменения: Thu Jan 6 20:48:06 2005
Дата индексирования: Tue Oct 2 03:05:06 2012
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Поисковые слова: jupiter
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Moving Towards Life
How did chemisty
and oceans produce this?
Remember the two keys to evolution of planetary atmospheres:
- Fate of the water vapor (gaseous, liquid, solid)
- Fate of the Carbon Dioxide (stays in atmosphere vs. dissolves
in liquid water)
After condensation of water vapor produced the earth's oceans, thus
sweeping out the carbon dioxide and locking it up into rocks, our
atmosphere was mostly nitrogen.
So now let's make some life over the next billion years or so:
Amino Acids now loosely mixed in the oceans
So now we have some amino acids (monomers) loosely mixed in the oceans.
Liquid medium is important:
- Protects molecules from UV photon disruption
- Ease of transport and Interaction
Next goal is to combine monomers into Polymers (peptide chains)
How did chemisty
and oceans produce this?
Cells Today:
- concentration of monomers and enzymes and proteins which
act as an energy source
- O and OH are removed (hydration)
- monomers join together to make polymers
4 Billion years ago:
- NO cells
- need to concentrate monomers together to facilitate polymer
formatoin
Step 2: Concentrate the Monomers:
- Local Evaporation (clays) Tides ?
- heat from expelled lava (St. Helens)
- tidal pools (bigger tides)
- freezing of water
Energy Sources:
- lightning (Jupiter)
- heat
- UV
All of the above are quite inefficient compared to enzymes
Clays Silicate Surfaces acts as a catalyst
Peptide chains of around 100 amino acids can be found today
Does the reaction on the silicate surfaces favor L amino acids?
Step 3: BIG, Unknown Next Step need to organize a system
capable of self-replication (e.g. DNA)
- Organic polymers in high concentration seperate out from
liquid medium as individual droplets proto-cells
- long chain molecules can act as a membrane
EVOLTUIONARY ADVANTAGE: Polymers that could reproduce themselves will
survive
- Trial and Error until "right" combination is acheived (DNA)
- every living organism on the earth has DNA
- Fossil Record indicates that single celled life first emerged
3.5 billion years ago
- Therefore it took one billion years to go from atmospheric
chemistry to blue green algaes via the oceanic pathway
- All you need is time?
Now we have a multiplying population of bacteria (prokaryotes) that
has to eat to survive:
What to eat?
- First feed off other organic molecules
via fermentation
- fermentation is very inefficient, releases little energy
- Big problem the food supply is running out
EVOLTUIONARY ADVANTAGE: Bacteria that could process plentiful UV light
and INorganic molecules will survive
- are most plentiful molecules
dissolved in the oceans
- requires least amount of energy to
break apart
- early blue green algae therefore metabolized
giving off sulfur as a waste product stinky anerobic photosynthesis
- Important photosynthesis evolved from a need for the bacteria
to be able to feed themselves and multiply