Transcript BioH Ch 19 Origin of Life 2013

History of Life on Earth
How long has life been on Earth?
What are the relationships between
organisms as time moved forward?
BioH - Ch 19
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Early Earth
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Early Earth Atmosphere
•Hydrogen
Cyanide
•Carbon
Dioxide
•Carbon
Monoxide
•Nitrogen
•Hydrogen
Sulfide
•Water
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Experimental Evidence
The spontaneous formation of organic molecules was first demonstrated
experimentally in the 1950s, when Stanley Miller (then a graduate student)
showed that the discharge of electric sparks into a mixture of H2, CH4, and
NH3, in the presence of water, led to the formation of a variety of organic
molecules, including several amino acids.
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• At the end of one week, Miller
observed that as much as 10-15%
of the carbon was now in the form
of organic compounds.
• Two percent of the carbon had
formed some of the amino acids
which are used to make proteins.
• Perhaps most importantly, Miller's
experiment showed that organic
compounds such as amino acids,
which are essential to cellular life,
could be made under the
conditions that scientists
believed to be present on the
early earth.
Miller’s Experiment
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“Agents” of Metabolism
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Origin of Prokaryotic cells
• The next step in evolution was the
formation of macromolecules.
• The monomeric building blocks of
macromolecules have been
demonstrated to polymerize
spontaneously under plausible
prebiotic conditions. Heating dry
mixtures of amino acids, for example,
results in their polymerization to form
polypeptides.
• But the critical characteristic of the
macromolecule from which life
evolved must have been the ability to
replicate itself. Only a macromolecule
capable of directing the synthesis of
new copies of itself would have been
capable of reproduction and further
evolution.
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Next Steps
 Only nucleic acids are capable of selfreplicating through complimentary basepairing.
 These self-replicating “units” may have
been enclosed in a double layer of
phospholipids.
 This would be considered the “first cell”.
 Because cells originated in a sea of organic molecules, they were able to
obtain food and energy directly from their environment.
 But such a situation is self-limiting, so cells needed to evolve their own
mechanisms for generating energy and synthesizing the molecules necessary
for their replication.
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Evolution of Metabolism
 The generation and controlled
utilization of metabolic energy is
central to all cell activities, and
the principal pathways of energy
metabolism are highly conserved
in present-day cells.
 All cells use adenosine 5′triphosphate (ATP) as their
source of metabolic energy to
drive the synthesis of cell
constituents and carry out other
energy-requiring activities, such
as movement (e.g., muscle
contraction).
 Generation of metabolic energy, using
glycolysis - the anaerobic breakdown of
glucose to lactic acid to produce ATP.
 Photosynthesis utilizes energy from sunlight to
drive the synthesis of glucose from CO2 and
H2O, with the release of O2 as a by-product.
 The O2 released by photosynthesis is used in
oxidative metabolism, in which glucose is
broken down to CO2 and H2O, releasing much
more energy than is obtained from glycolysis.
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Endosymbiotic Theory
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Common view of evolution of life forms
See text: Pages 306-307
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Where does this lead?
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