BIO 104 4/1/96
Introduction to the course (two handouts: course syllabus & laboratory topics)
The Origin of Life (chapter 3 in Raven & Johnson Text)
-How did life originate?
This idea is relatively recent; Oparin introduced a hypothesis in his
book about the origins of life (1936)
Almost everyone from the time of Aristotle to the middle of the nineteenth century,
believed that animals could be generated from non-living matter. This is called:
Abiogenesis: living things arise by "spontaneous generation" from non-
living matter.
-Aristotle (he was not a scientist, but a philosopher. 384-322 BC)
-Matter was injected with a life force or "soul".Only after the soul enters the matter does life originate.
-Virgil (70-19 B.C.) writing in the Georgics suggested a technique for producing swarms of insects
-Paracelsus (1493-1541) A Swiss medical philosopher offered a formula for the creation of human beings (bury a bottle in a dung heap)
-Jean Baptiste Van Helmont (1577-1644) a physician thought that the "germinating principle" in human sweat will generate live mice.
Biogenesis: life comes from previously existing life.
-Francisco Redi (1650)
He conducted an experiment which disproved the spontaneous generation of flies . He placed a
piece of dead meat in the bottom of a flask and noted that flies were present. Later he observed
maggots and the flies emerging from the meat. He covered the flask with a solid cover observed
that no maggots or flies emerged from the meat. Some argued that the solid cover excluded the
"life force" from entering the flask. So, Redi cover the flask with a gauze-like material so that
no flies could enter, but the "life force" could. The result no maggots or flies emerged from the
dead meat. Flies do not arise by spontaneous generation!
-Anton Van Leeuenhoek (1632-1723)
-inventor of the microscope
-he discovered microbes
-many people thought that microbes arise by spontaneous generation
-As a result of his observations, the French Academy of Science in the early 1860's awarded a prize to anyone who could conclusively prove that microbes were produced by biogenesis and NOT abiogenesis.
-Theodore Schwann (1837)
Conducted an experiment in which he heated air going through
a tube into a flask. The broth in the flask was sterile, but people
said that the experiment was not conclusive due to the fact heat may destroyed the
"life force".
-Louis Pasteur
-awarded the French Academy awarded him the prize in 1862
-He conducted the definitive experiment by utilizing a "swan neck"
flask.
Biology 104 Tuesday April 2, 1996
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.