BIO 104 4/2/96

Biogenesis
     -Louis Pasteur
          -Through his experiments the idea of spontaneous generation 
     was put to rest.  He concluded that life indeed comes from
     previously existing life. He said in 1864 "There is no condition known today in which     you can affirm that microscopic beings come into the world without germs, without    parents like themselves"

Where did life begin?
     Origin of Life
          3 possibilities:
               1) Life came from outerspace or extraterrestrial means (Jim Watson).
               2) Life was created through divine or supernatural means
               -Both of these cannot be observed thus out of the realm of
               science.
               3) Life began through interaction among molecules.  
     The Earth
          age:  4.5-5 billion years old
          Life may have begun 3.1 billion years ago.
          -The Calendar Analogy
               -1 day= 12 million years
                    Jan.= beginnings of the earth
                    July= earliest life 
                    Nov.= lower forms of life appear
                    Dec. 11= first land plants
                    Dec. 18= reptiles
                    Dec. 27= mammals
                    Dec. 31 10pm= humans appear
                    Dec. 31 11:59:30pm= written history
     Archaebacteria
          -use a form of photosynthesis called chemosynthesis.
          -anaerobic bacteria
          
     The Single Day Analogy of life:

          * see figure 3.11 A clock of biological time - page 59
     - A billion seconds ago it was 1957
     - A billion minutes ago Jesus was alive and walking in Galilee
     - A billion hours ago, the first humans had not yet been born
     - A billion days ago, no biped walked on earth
     - A billion months ago, dinosaurs had not yet been born
     - A billion years ago, no creature had ever walked on the face of the earth
     (it would take 31.7 years to go back a billion years if one second equaled one year)

          This analogy of the succession of life shows us that life must have begun in    water. 

     Formation of the Earth
          -When cosmic dust came together by gravity, the heavier elements
          went towards the center creating a light troposphere and 
          atmosphere

"The Origin of Life" by George Wald
     -if a chance event has a possibility then we can assign it a probability,
     and given enough trials that probability becomes an inevitability.

Al Oparin (1936) Origins of life
     Assumptions:
          1) Primitive atmosphere composed of 
               -H2O
               -CH4 (Methane)
               -N2
               -NH3 (Ammonia)
               -H2
          "reducing atmosphere"
          CH4, H2O, and NH3 can yield nucleotides and amino acids
          CH4, and H2O can yield alcohols, carbohydrates, and fatty acids
               -they could also form colloids
          2) Colloids-hydrophobic and hydrophilic properties.
               -formation of coacervates
                    -RNA was a catalyst and able to replicate itself
                    -coacervates can be made by "chance,"  RNA can act like
                    an enzyme

Stanley Miller - tested Oparin's hypothesis
     He simulated the atmosphere of the early earth and introduced electrical
charges to the gas, to simulate lightning.  The reactions that followed produced
detectable amount of amino acids and complex organic molecules.  This experiment was
consistent with Oparin's hypothesis.  See page 52 in the textbook.
          -early Earth was devoid of oxygen 
          -heterotropes:  organisms that eat other organisms
          -Archaebacteria used anaerobic respiration, which does not require
          oxygen.

Evolution of Photosynthesis
     -allowed for development of autotrophs
     1) CO2+H2O yield organic compounds
     2) the byproduct is O2 which is essential in oxidative metabolism
     3) Oxygen forms the ozone layer which block ultra violet rays, this 
          enabled land development.
     -Thus, all life must have arisen in water.