Transcript origin of life

The Big Bang theory of the
formation of the universe
• All material in the universe
was created in a huge
"explosion," creating and
defining matter and space.
• The sudden cooling of the
superheated ejecta facilitated
the combination of atomic
components into atoms and
molecules.
• These clouds of gasses
eventually cooled and
formed the principle
components of galaxies including stars and planets.
Formation of the solar system
A. The earth formed approximately 4.6
BYA (billion years ago.) Initially,
there was a cloud of gasses and
dust particles, possibly originating
from the ejected particles of a
nearby supernova.
B. The cloud gradually contracted and
flattened, concentrating about 99%
of its mass in the center with the
rest rotating counterclockwise in a
flattened disk.
C. As the disk rotated, turbulence was
created, causing condensation of
the disk into small, turbular eddies.
These gradually accreted together
to form protoplanets.
D. These protoplanets further accreted,
creating the mature planets of the
solar system.
Origin of life
Oparin-Haldane hypothesis.
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The atmosphere of the early Earth may have been chemically reducing in
nature, composed primarily of
methane (CH4),
ammonia (NH3),
water (H2O),
hydrogen sulfide (H2S),
carbon dioxide (CO2) or
carbon monoxide (CO), and
phosphate (PO43-), with
molecular oxygen (O2) and
ozone (O3) either rare or absent.
In such a reducing atmosphere, electrical activity can catalyze the creation of
certain basic small molecules (monomers) of life, such as amino acids.
This was demonstrated in the Miller–Urey experiment by Stanley L. Miller
and Harold C. Urey in 1953.
Phospholipids (of an appropriate length) can spontaneously form lipid
bilayers, a basic component of the cell membrane
These organics, accumulated in the surface waters of the ocean, forming a
"primordial soup", out of which, in time, life in its most elementary form
emerged
Oparin-Haldane model
The steps of the Oparin-Haldane model are
described below.
• 1) Organic molecules including amino acids and
nucleotides are synthesized abiotically (without
living cells).
• 2) Organic building blocks in the prebiotic soup
are assembled into polymers of proteins and
nucleic acids.
• 3) Biological polymers are assembled into a selfreplicating organism that fed on the existing
organic molecules.
Miller-Urey Experiment
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Diagram of the Miller-Urey apparatus
Conducted in 1953 by Stanley Miller
under the supervision of Harold Urey;
the first experiment to test the OparinHaldane theory about the evolution of
prebiotic chemicals and the origin of
life on Earth.
1. A mixture of methane, ammonia,
hydrogen, and water vapor, to simulate
the version of Earth's primitive,
reducing atmosphere proposed by
Oparin, was introduced into a 5-liter
flask and energized by an electrical
discharge apparatus to represent
ultraviolet radiation from the Sun.
2. The products were allowed to
condense and collect in a lower flask
which modeled a body of water on the
Earth's surface.
3. Heat supplied to this flask recycled the
water vapor just as water evaporates
from lakes and seas, before moving
into the atmosphere and condensing
again as rain.
Miller-Urey Experiment
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After a day of continuous operation,
Miller and Urey found a thin layer of
hydrocarbons on the surface of the
water.
After about a week of operation, a dark
brown scum had collected in the lower
flask and was found to contain several
types of amino acids, including glycine
and alanine, together with sugars, tars,
and various other unidentified organic
chemicals
The conditions were:
A gaseous phase containing reduced
sources of carbon (methane), nitrogen
(ammonia), oxygen atoms (water), and
hydrogen atoms from any or all of
these precursors as well as hydrogen
gas.
Electrical energy provided by spark
discharge.
Ambient temperature between 0 and
100 C.
Sterile conditions to begin with (abiotic
environment).
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Apparatus used in the Miller-Urey
experiment
microspheres
• Fox was best known for his seminal experiments
in the synthesis of thermal proteins (previously
known as "proteinoids") from amino acids which
he carried out in the 1960s and for his
demonstration that these proteins, when placed
in water, spontaneously self-organize into
structures, known as microspheres, that
resemble primitive cells.
• His most recent experiments sought to
demonstrate that the cell-like structures he
created in the laboratory also act as protonerve
cells
Microspheres
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Microscopic, firm spherules which form on
the cooling of hot saturated solutions of
proteinoids.
They were first reported in 1959 by Sidney
Fox, K. Harada, and J. Kendrick who
proposed that microspheres might
represent a significant early stage in
precellular evolution.
It has been suggested that their greater
stability makes them a better proposition in
this regard than coacervates.
One milligram of proteinoids can yield 100
million microspheres, ranging from 1.4 to
about 2.5 microns in diameter.
Microspheres have been observed to retain
their form for several weeks and, when
sectioned, may display a double-walled
structure.
Recently, Fox argued that microspheres
also display characteristics of primitive
nerve cells.
Coacervates
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Their name derives from the Latin coacervare,
meaning to assemble together or cluster
Coacervates measure 1 to 100 micrometers across,
possess osmotic properties, and form spontaneously
from certain weak organic solutions
A spherical aggregation of lipid molecules making up a
colloidal inclusion which is held together by
hydrophobic forces.
It was suggested by Oparin that coacervates may have
played a significant role in the evolution of cells.
In water, organic chemicals do not necessarily remain
uniformly dispersed, but may separate out into layers
or droplets.
If the droplets which form contain a colloid rich in
organic compounds and are surrounded by a tight skin
of water molecules then they are known as
coacervates.
These structures were first investigated by
Bungenburg de Jong in 1932.
A wide variety of solutions can give rise to them; for
example, coacervates form spontaneously when a
protein, such as gelatin, reacts with gum arabic.
Origin of life
• Stage 1: The formation of the earth and atmosphere is
considered the first stage in the long trek from inanimate
matter to life. This stage provided the inorganic raw
materials for the evolution of life and set up the conditions
for their interaction.
• Stage 2: The second stage produced organic molecules
through interactions between inorganic substances,
driven by energy sources such as lightning and ultraviolet
radiation from the sun.
• Stage 3: In the third stage, the organic molecules present
assembled randomly into collections capable of chemical
interaction with the environment. As the collections
formed, interactions taking place within them produced
still more complex organic substances, including
polypeptides and nucleic acids. Some of these collections
of molecules were capable of carrying out primitive living
reactions. There is little agreement on the form taken by
the first spark of life in these primitive aggregates.
Origin of life
• Stage 4: In the fourth stage, a genetic code
appeared in the primitive living aggregates. This
code regulated duplication of information
required for reproduction of the aggregates and
established the link between nucleic acids and
the ordered synthesis of proteins. Things were
still pre-cellular, but with these developments
(directed synthesis and reproduction), life was
fully established in the molecular assemblages.
• Stage 5: The fifth and final stage involves
conversion of the pre-cellular assemblages into
fully organized cells with a nuclear region and a
cytoplasm, all enclosed by an outer boundary
membrane--a plasma membrane.
Eukaryotic cells are actually the descendents of
separate prokaryotic cells
• Evidence supports the idea that eukaryotic cells are actually
the descendents of separate prokaryotic cells that joined
together in a symbiotic union.
• In fact, the mitochondrion itself seems to be the "great-greatgreat-great-great-great-great-great-great granddaughter" of a
free-living bacterium that was engulfed by another cell,
perhaps as a meal, and ended up staying as a sort of
permanent houseguest.
• The host cell profited from the chemical energy the
mitochondrion produced, and the mitochondrion benefited
from the protected, nutrient-rich environment surrounding it.
• This kind of "internal" symbiosis - one organism taking up
permanent residence inside another and eventually evolving
into a single lineage - is called endosymbiosis.