Transcript ORIGIN OF LIFE Chapter 14

ORIGIN OF LIFE
Chapter 14
Topics:
Biogenesis
Earth’s History
First Life Forms
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Spontaneous Generation
 Living things can arise from non-living things
 Many believed that the air had some sort of capacity
to generate life
 Invisible “ether”
 Widely accepted theory of the origin of living
things until ~1600s
 As the scientific theory took hold, many began
to discard this view
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Biogenesis
 All living things come from living things
 Many began to challenge the theory of
spontaneous generation in favor of biogenesis
 But, these scientists had rough road ahead to
change the minds of many
 Redi
 Spallanzani
 Pasteur
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Francesco Redi
 Italian scientist 1626-1697
 He hypothesized maggots/flies arose from
meat that had been infested with the fly eggs.
 He set up experiment with a control group of
meat with no cover and an experimental group
of meat with a cover to keep the flies out
 Control group became infested with maggots
 Experimental group remained maggot-free
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Lazzaro Spallanzani
 Italian scientist 1729-1799
 He theorized that the microorganisms found in
food came from pre-existing organisms not
from the air – folks still did not believe Redi’s
results
 Set up an experiment to test his hypothesis
 Control group – boiled meat broth, left open to
air after boiling
 Experimental group – boiled meat broth,
sealed immediately after boiling
 Results – no microorganisms in sealed
container
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Louis Pasteur
 French scientist 1822-1895
 He took Spallanzani’s work one step farther – he also
believed these microorganisms are in the air and
contaminate food
 He set up an experiment similar to Spallanzani’s
except he did not seal experimental group flasks
 Instead, he designed a special crooked neck flask to
allow air in but trap any organisms before they could
enter the sterile broth
 His broth remained open to air, but microorganism- free
for more than a year.
 So air is not able to spontaneously generate life
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So how did “it” all begin?
 As humans entered into this new age of
enlightenment, they began to question
not only what gives rise to living things,
but how did life and Earth begin.
 As you know, often finding answers takes
a long time and humankind needed to
acquire the tools and knowledge to find
the answers to the questions that plague
us all.
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Big Bang
 Current theory contends that “it” all began as a
singularity.
 This is something with infinitely large mass but
packed into an infinitely small volume with a
huge magnetic force.
 This singularity simply expanded, so the term
“big bang” is a bit of a misnomer – there was
no explosion, but a big expansion
 At that instant all the matter, energy, and forces
that exist now came into existence
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Big Bang…
 This expansion occurred ~13.7 B years ago.
 The matter from the singularity moving outward
at great speed and at extremely high
temperature.
 Swirling masses of matter eventually formed
our solar system and our Earth about 4.5 B
years ago
 The universe is still expanding and we are now
able to detect the faintest radio emissions
dating from the time of the Big Bang, enabling
scientists to better date that event.
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How do we know the age
of Earth?
 Primarily from radioactive dating methods
 Radioactive elements break down and decay
into more stable elements
 Half-life is the time it takes for ½ of a sample of
a radioactive element to decay
 Carbon-14 has a ½ life of 5730 Years
 C-14 used to date organic material
 Uranium-238 has a ½ life of 4.5 Million Years
 U-238 used to date inorganic material
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Early Earth
 But the surface cooled and water formed to
cover much of the surface
 Early Earth compounds very different from
modern
 Early atmosphere reducing atmosphere (CO2,
H2S, CH3)
 But many scientists thought this primordial
soup of the ancient oceans gave rise to the
first organic molecules that led to the
beginning of life
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Stanley Miller & Harold
Urey
 At the University of Chicago in the 1950s, they
devised & conducted an experiment to make
organic compounds from this primordial soup
 They created an apparatus to contain this
ocean mixture; using electricity to simulate
lightning strikes
 Experiment yielded: amino acids, ATP, &
nucleotides – all the necessary components of
a living cell
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Lerman’s Bubble Model
alternative to “primordial soup” model
 Proposed in 1986 by geophysicist Louis Lerman
 Suggests that chemicals necessary for life found in
bubbles at the ocean surface
 Bubbles produced at deep sea ocean vents, trapping
escaping gases (NH3, CH3) in bubbles
 The bubbles essentially protected compounds from
UV degradation & concentrated them; rxns leading to
amino acids thus occurred safely & faster
 As bubbles burst at ocean surface, UV radiation and
lightning energy provided E for further rxns, creating
the molecules required by living organisms
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http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AbioticSynthesis.html
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How do we get from
molecules to a cell?
 This is one question to which there is no
good answer – at least not yet.
 However, many organic molecules
naturally coalesce when in solution and
scientists theorize that this is what
happened
 Microspheres – protein molecules that group
 Coacervates – molecules of different types
linked by amino acids and sugars
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Terms
 Autotrophe – organism that uses E to synthesize organic molecules
from inorganic material
 Heterotrophe – organism that obtains organic “food” molecules by
eating other organisms or their by-products
 Prokaryote – cell with no nucleus, no membrane-bound organelles
 Eukaryote – cell with nucleus and membrane-bound organelles
 Photosynthesis – production of carbohydrates by using E from light
 CO2 + Light + H2O  C6H12O6 + O2
 Chemiosynthesis – production of carbohydrates by using E from
inorganic sources NOT light
 Glycolysis – first step to making ATP
 If oxygen present, aerobic respiration occurs
 If no oxygen present, fermentation occurs
 Fermentation – pathway for breaking down organic molecules when
NO oxygen is present
 Cellular Respiration – process by which cells make ATP by breaking
down organic compounds
 Aerobic Respiration – process of making ATP, oxygen is final electron
acceptor
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Archaebacteria –
to early living cells
closest link
- Early bacteria were autotrophic – using
chemosynthesis not photosynthesis (remember no
sunlight getting thru the thick cloud layer)
- They were able to survive harsh environments
(remember the atmosphere is full of poisonous gases and it is still
pretty hot)
- Some of these acquired the ability to
photosynthesize by 3 billion years ago
- Oxygen (O2) was the by product of these cells & it
built our modern atmosphere
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Eukaryotes
 Current theory as to how these arose is the
Endosymbiotic Theory proposed by Dr. Lynn
Margulis.
 Somehow a prokaryote entered another
prokaryote; a symbiotic relationship ensued;
the organism reproduced
 The “inside” prokaryote became the chloroplast
and mitochondria of today’s eukaryotic cells
 Remember mitochondria and chloroplasts have their
own DNA
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