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Chapter Chapter 3

BIOL 1000 Chapter Notes - Chapter Chapter 3: Alexander Oparin, Reducing Atmosphere, Homeostasis

Course Code
BIOL 1000
Nicole Nivillac
Chapter 3

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Chapter 3 Defining Life and its Origins Pages (53-71)
The Cell and Evolution:
Introduction to Evolution and Evolution of Eukaryotes
3.1: What is Life? remember abiotic means nonliving
All life displays:
1) Order
2) Harnesses
3) Utilizes Energy
4) Reproduces
5) Responds to stimuli
6) Exhibits homeostasis
7) Grows, develops, and evolves
According to the most widely accepted hypothesis, all components of the solar system were
formed at the same time by the gravitational condensation of matter present in an interstellar
which initially consisted of hydrogen.
-Intense heat and pressure generated in the central region of the cloud formed the sun
-The remainder of the spiraling dust and gas condensed into the planets.
-It is estimated that it took approximately 500 million years to cool to temperatures that could
nurture the development of life.
-Because of the importance of water for the development of life, the region of space around a star
where temperatures would allow for liquid water is termed “habitable zone.
-All forms of life are composed of the major macromolecules including nucleic acids, proteins,
lipids, and carbohydrates.
The primordial atmosphere probably contained an abundance of water vapour from the
evaporation of water at the surface as well as large quantities of hydrogen, carbon dioxide,
ammonia and methane. There was an almost complete absence of oxygen.
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-Two scientists : Aleksander Oparin and John Haldane, independently proposed that
organic molecules could have formed in the atmosphere of primordial earth.
Oparin Haldane Hypothesis: The early atmosphere was a reducing atmosphere
because of the presence of large concentrations of molecules such as hydrogen, methane… These
molecules contain an abundance of electrons and hydrogen and would have entered into
reactions with one another yielding larger and more complex molecules.
-Todays atmosphere is considered as an oxidizing atmosphere. The presence of oxygen prevents
complex, electron rich molecules from being formed because oxygen is a strong oxidizing
molecule and would itself accept the electrons from organic molecules and be reduced to water.
-The lack of oxygen in the primordial atmosphere meant that there was no ozone (O3) layer. It
was hypothesized that without the ozone layer, energetic ultraviolet light was able to reach the
lower atmosphere, providing the energy needed to drive the formation of biologically important
HYPOTHESIS #2 Deep Sea Vents:
-Complex organic molecules could have originated on the ocean floor at the site of deep sea
hydrothermal vents.
-These cracks are found around the globe near sites of volcanic or tectonic activity and release
superheated nutrient rich water at very high temperatures (300 degrees) as well as the reduced
molecules including methane, ammonia, and hydrogen sulfide.
HYPOTHESIS #3 Extraterrestrial Origins:
-It is entirely possible that the key organic molecules required for life to begin came from space.
Each year many meteorities impact Earth many of which belong to the class called carbonaceous
chondrites. Murchison meteorite landed in Victoria, Australia showed that it contains an
assortment of biologically important molecules including amino acids such as alanine as well as
purines and pyrimidines.
Life Requires the Synthesis of Polymers:
-Molecules such as amino acids and nucleotides are monomers.
How were polymers that are required for life made without sophisticated enzymes?
Answer: The Clay Hypothesis
3.3: Lipid Spheres May have led to the Development of Cells:
-A critical step along the path to life is the formation of a membrane defined compartment
Allowing for metabolic reactions to take place in different environments.
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