Transcript Chapter 14 – The Origin of Life

What is Biogenesis?
 Biogenesis states that all living things come from
other living things
 spontaneous generation
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Before the 1600’s
A process in which something arises from nothing
What Caused the Downfall of Spontaneous
Generation?
 Redi’s Experiment
 It was widely accepted that flies spontaneously
generated from rotting meat.
 Francesco Redi studied the developmental forms of flies
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He saw that maggots were often found places after adult flies
had previously landed
He noted that maggots ultimately led to the development of
adult flies
What Caused the Downfall of Spontaneous
Generation?
 In 1668 Redi conducted an experiment to prove that maggots
could only come from adult flies, and not rotting meat
Uncovered Jars
Maggots Appear

Covered Jars
No Maggots Appear
His results showed that files only came from eggs, in
opposition to the idea of spontaneous generation
What Caused the Downfall of Spontaneous
Generation?
 Spallanzani’s Experiment
 1700s, Lazzaro Spallanzani tested spontaneous generation
of microorganisms
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He boiled one flask of meat broth and immediately sealed it
after boiling
He boiled another flask of meat broth and let it sit out unsealed
Sealed flasks remained clear
Unsealed flasks became cloudy from microorganisms
What Caused the Downfall of Spontaneous
Generation?
Broth is boiled.
Flask is
open.
Broth becomes cloudy
with microorganisms.
Broth is boiled.
Flask is
sealed.
Broth is free of
microorganisms.
What Caused the Downfall of Spontaneous
Generation?
 Pasteur’s Experiment
 Louis Pasteur set out to confirm that spontaneous
generation is not possible in the mid-1800s
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Pasture conducted a similar experiment to Spallanzani
instead of sealing the flask shut, he made a curved-neck flask
that allowed air in, but kept microorganisms out
After boiling, the broth remained clear for a year
He broke the neck off of his flask, and the broth became
contaminated with microorganisms
The led to the downfall of spontaneous generation, and the
acceptance of biogenesis
What Caused the Downfall of Spontaneous
Generation?
Broth is boiled.
Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with
microorganisms.
What was Earth’s Early History?
 The Formation of the Earth
 The estimated age of the Earth is over 4 billion years old
 Radiometric dating allowed scientists to determine
the age of the Earth
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Isotopes
 atoms of an element with a different number of neutrons
Mass number of an isotope
 the total number of protons and neutrons for an atom
What was Earth’s Early History?
 Some isotopes have unstable nuclei that undergo
radioactive decay
 Half-Life
 The length of time that it takes for one-half of any size sample of
an isotope to decay
 The age of a material can be determined by measuring
the amount of a particular radioactive isotope it contains
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Carbon-14 is a radioactive isotope of carbon. Scientists can
compare the amount of carbon-14 found in a sample to the
amount of carbon-12 (which is not radioactive) to determine the
sample’s age
 To determine the age of the Earth, scientists use the
decay of uranium and thorium isotopes found in rock
crystals
Radioactive Decay
What Were the First Organic
Compounds?
 The First Organic Compounds
 All of the elements found in organic compounds are
believed to have existed on Earth and in the rest of the
solar system when Earth was formed
 How did they form the organic compounds found in
life?
What Were the First Organic
Compounds?
 Simple Organic Molecule Formation
 “The Primordial Soup Hypothesis”
▪
▪
▪
Alexander Oparin thought that Earth’s early atmosphere was
VERY different than it is today
He believed it was made of ammonia, hydrogen gas, water vapor
and compounds made of carbon and hydrogen
He believed these gases could have produced the first organic
compounds in the early oceans
What Were the First Organic
Compounds?
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UV light from the sun, and energy from lightening could
have been the energy sources needed to fuel these
reactions
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As the Earth cooled, and water vapor condensed to form
lakes and seas, the organic compounds could be found in
the water
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Over time, the organic compounds could have undergone
chemical reactions (fueled by lightening and UV
radiation) to form biological macromolecules
What Were the First Organic
Compounds?
 Stanley Miller and Harold Urey
 1953
 Used Oparin’s hypotheses to conduct experiments that
resulted in the production of organic compounds
 Recently, is has been suggested that Earth’s
atmosphere was made of CO2, water vapor and N2
gas
 These conditions would not allow for the production of
organic compounds
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Some hypothesize that areas found by undersea hot springs may
have produced organic compounds
Miller and Urey
Mixture of gases
simulating
atmospheres of
early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
Cold
water
cools
chamber,
causing
droplets
to form
Liquid containing
amino acids and
other organic
compounds
How Were the First Cells Formed?
 From Molecules to Cell-like Structures
 Cell-like structures that may have led to the first cells
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Microspheres
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Coacervates
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made of many protein molecules in a membrane
collections of droplets that are made of molecules like amino acids and sugars
Both of these form spontaneously in certain kinds of solutions.
Microspheres can bud to form smaller microspheres, while
cocervates can grow
These cell-like structures are NOT alive and also lack hereditary
characteristics
What Were the First Life Forms?
 The origin of Heredity
 The first molecule that held hereditary information may
have been RNA rather than DNA.
 serve as a template for protein assembly
 some RNA molecules can act as self-replicating enzymes
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called ribozymes.
What Were the First Life Forms?
 The First Prokaryotes
 When the first organisms arose, there was no oxygen,
which means they were anaerobic
 It is believed that the first prokaryotic cells were
heterotrophs
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feeding on organic molecules
 This resulted in the need for autotrophic organisms
What Were the First Life Forms?
 Chemosynthesis
 no oxygen
 the first autotrophic cells did not use photosynthesis
 These cells used chemosynthesis to produced food
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CO2 is used as the carbon source
The energy comes from inorganic substances like sulfur
 Archea are prokaryotic cells living today in harsh
environments that used chemosynthesis
What Were the First Life Forms?
 Photosynthesis & Aerobic Respiration
 Photosynthetic organisms such as cyanobacteria
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produced O2 as a byproduct of photosynthesis
 Since O2 could damage enzymes essential for life,
organisms developed a way to bond O2 to other
compounds to prevent damage
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Scientists believe this was one of the first steps in aerobic
respiration
 It took a billion years for the O2 levels to reach where
they are today
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As the O2 reached the upper levels of the atmosphere, it reacted
with the UV radiation from the sun forming the ozone
What is Endosymbiotic Theory?
 The First Eukaryotes
 Eukaryotes developed from endosymbiosis
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a mutual relationship between two prokaryotic cells
A small, aerobic prokaryote entered a larger prokaryote and was
able to live and reproduce
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modern day mitochondria
There was a second, successful invasion in which a small,
photosynthetic cell was able to live and reproduce in a larger
prokaryote
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chloroplasts
What is Endosymbiotic Theory?
Chloroplast
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Plants and
plantlike
protists
Photosynthetic
bacteria
Primitive Photosynthetic
Eukaryote
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
Animals, fungi, and
non-plantlike protists
What is Endosymbiotic Theory?
 Evidence for Endosymbiont Theory
 Mitochondria and chloroplasts have their own DNA
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Their DNA is circular, similar to prokaryotic DNA
 Mitochondria and chloroplasts have ribosomes similar
to prokaryotic cells
 Mitochondria and chloroplasts reproduce by binary
fission, independent from the rest of the cell