Origin of Life
Chia sẻ bởi Nguyễn Hoàng Quí |
Ngày 24/10/2018 |
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ORIGIN OF LIFE
The facts……. hidden somewhere
The story….….. unrevealed
The truth….. not known exactly
The path…. untraced
An attempt to explore the way!!!
An effort to blend biology, chemistry, and physics in the search to identify and understand the origin of life in the universe
It’s a “Journey Back In Time”…
By Kalpana Stuti, Ritu, Gauri
Miranda House
ORIGIN OF LIFE
BIG BANG
Cosmic dust and gases+ H2O
Oceans
Haldane soup
Reducing atmosphere(gases like CH4,NH3,N2,CO2,H2O responsible for abiotic synthesis of organic compounds)
OPARIN-HALDANE THEORY
Haldane Soup
Simple Molecules
Complex Molecules (building blocks)
Aggregates (coacervates and microspheres)
Protocells( proprimitive stage before formation of true cell
Proto cells + nucleic acid = self replicating system
“CELL”
Microsphere
ENERGY YIELDING SYSTEM
“Cell”
Energy Yielding System
Chlorophyll development
Photosynthesis
O2 evolved
Ozone Formation (shielding effect)
Atmosphere changed to oxidizing from reducing.
Evolution of photosynthesis which is followed by respiration.
CELL
Replication
Metabolism
Homeostasis
Anaerobes
Aerobes
Chemotrophs
Heterotrophs
Chemoheterotrophs
Chemoautotrophs
Prokaryotic Cells
Eukaryotic cell
Endosymbiotic Theory
How Eukaryotic Cell Changed to Multicellular Organism….
EVIDENCES???
Geological Evidence
Precambrian Fossil Evidence
Laboratory Evidence
GEOLOGICAL EVIDENCE
Sedimentary rock in past 500 million years are silicate sands clay, quartz type indicating oxidizing conditions.
Ancient Precambrian sediments containing sands with reduced iron minerals found in Canada, Brazil, South Africa.
Banded iron ore deposits with mixed oxidation states in Quinland, Russia, India and Australia
PRECAMBRIAN FOSSIL EVIDENCE
Elso Barghoorn et al studied polished thin sections of silica rich cherts from Gunflint region of Northern Minnesota and Southern Canada with optical and electron microscope.
Living organisms algae, fungi, microbes associated with banded iron ore cherts indicates that they were probably laid down under reducing atmospheric conditions.
LABORATORY EVIDENCE MILLER & UREY EXPERIMENT
A mixture of H4,NH3, H2, and water was put into a flask and energized by an electrical discharge apparatus to represent ultraviolet radiation .
The products were allowed to condense and collect in a lower flask.
. After a week, Miller and Urey found a dark brown scum had collected in the lower flask and was found to contain several types of amino acids together with sugars, tars, and various other unidentified organic chemicals.
How could polymer form in dilute aqueous solution when polymerization is a dehydration process?
Sidney Fox experiment – Fox found that dry amino acids heated to 160-210OC, forms polymers of molecular weight 300,000 provided mixture contains Aspartic Acid and Glutamic Acid. Thermal protenoids so formed, if washed with water, form microspheres of fairly uniform diameter of 20, 000Ao
Cinder Cone Hypothesis - Protenoid material first polymerized on hot dry volcanic Cinder Cones and then it was leached into oceans by rains to form microspheres.
These became early segregated chemical systems and eventually led to protocells.
COACERVATES
They tend to concentrate some molecules in their interior and this in an ability that most primitive protocells would have acquired. Behavior of Coacervate shows how earlier protocells would have achieved internal compositions that were different from their surroundings and could have developed certain amount of chemical evidences.
Coacervate droplets formed by interaction between gelatin and gum arabic. A. I. Oparin
Amylase
Sunlight
Ascorbic Acid + Dye
Chloroplast e- + Dye
Reduced Dye (colour change)
Amylase
Starch
Maltose
PANSPERMIA THEORY
Organic compounds arrived from outer space
It states that hydrocarbons and other organic molecules (molecules that organisms contain or that might lead to the genesis of life) have been found in meteorites –
It means that at least prebiotic chemistry that leads to the primordial soup might be going on there.
Evidences in support of this theory
In 1969, a meteorite landed in Australia that was 12% water and contained traces of 92 amino acids.
Inference- It points to not only the presence of organic compounds in outer space, but also the capacity of such compounds to reach earth.
Fred Hoyle and Chandra Wickramasinghe have argued persistently since the 1970s that complex organic substances, and perhaps even primitive organisms, might have evolved on the surface of comic dust grains in space and then been transported to the Earth's surface by comets and meteorites.
Where did life begin???
There is an ongoing debate regarding the most probable site of life's origins.
The prevailing paradigm - life began near the ocean's surface, bathed in sunlight.
Current Research - life arose near deep hydrothermal vents which is still under investigation.
"Scientists have long suspected that life on Earth originated in the ocean and strong evidence now suggests that the earliest life on our planet occurred in the depths of the ocean in the absence of heat and light."
-- Pulse of the Planet, American Museum of Natural History
Miller and Urey found
Photograph from National Geographic magazine
Deep-sea Vents
Their discovery in late 1970’s stretched our concept of the origin of life on earth.
Can life exist and that too thousands of meters beneath the surface of sea in absence of sunlight?
It raised the possibility that earlier vents supplied the energy and chemical precursors for origin of protobionts.
Exploring the deep ocean floor
View of the first high-temperature vent (380°C) ever seen by scientists during a dive of the deep-sea submersible Alvin in 1979.
Such geothermal vents are called smokers.
This photograph shows a black smoker, but smokers can also be white, grey, or clear depending on the material being ejected. Photograph by Dudley Foster from RISE expedition
Vent Community
A vent community in its prime: Pale pink eelpout fish and white brachyuran crabs swim and scuttle among blood-red tube worms large and small. Scientists are still trying to figure out how the offspring of such organisms disperse over long stretches of inhospitable seafloor to colonize widely separated vent systems.
Giant Clams
The size of deep-sea giant clams is evident from the hands of a scientist holding them.
(Photograph by William R. Normark, USGS.)
Giant Tube Worms: RIFTIA
On the bottom of the ocean around deep-sea hydrothermal vents, there is a profusion of life that thrives on the hydrogen sulfide (H2S) gas released from the vents.and live inside hard, shell-like protective tubes that attach to the rocks.
Giant tubeworms that live around hydrothermal vents on the sea floor. These creatures are about the size of your hand in shallower waters, but in the ocean's deep they have been found as big as eight feet long!
How they live….
These creatures lack mouths, anuses, intestines and stomachs, and scientists were at a loss to explain how these were getting nutrients to survive and grow.
Their insides are lined with bacteria that oxidize the H2S, turning it into usable nutrients for the worms.
The bacteria, in turn, benefit from the relationship because the worms deliver blood containing hemoglobin which helps the bacteria to break down the sulfides.
They live in a symbiotic relationship with a bacteria that may hold clues as to how life on earth began billions of years ago.
BIOCHEMISTRY AT THE VENTS
H2S
Oxidation by bacteria
Energy released helps in fixing CO2 into small organic molecules
So this cycle ... is the same metabolic pathway that is utilized by plants in photosynthesis ... takes inorganic carbon dioxide and fixes it into organic compounds that are then food. But, the difference here, the critical difference, is that rather than using sunlight, these animals and bacteria are completely independent of sunlight. They utilize chemical energy to power that reaction.
So, ever imagined a life out of toxic Hydrogen Sulphide?!
Released from vents
Chemical of Life - Ammonia, Produced at Vents
Hydrothermal vents were the most likely site for NH3 production where inorganic sulphides acted as catalyst.
N2 +NO2 +N03
Presumed to be present in ancient sea
NH3
FeS, 500oC
89% yield, 15 min
FeO
46% yield 15 min
Powdered Basalt.
20% yield
Stable upto 800oC
RESULTS
Since NH3 cannot survive at temperature above 800oC indicates that nitrogen would have been present only as N2 during early phase of earth’s development.
Life can exist on thermal and chemical energy as opposed to just sunlight as had been thought in the past. And so what was realized is that photosynthesis was not the only way to support life.
What has been discussed so far…
In 1920s, Oparin and Haldane revived the doctrine of spontaneous generation in a more sophisticated form.
In 1953, American chemists Stanley Miller and Urey showed that some amino acids can be chemically produced from NH3 and CH4
in 1970s, Fred Hoyle and Chandra Wickramasinghe rekindled interest in Panspermia. They found evidences, traces of life, in the intervening dust.
In 1980’s the hunt for the most probable site of life’s origin began and then we came to deep sea hydrothermal vents.This discovery stretched our concept of the origin of life on earth.
Scientists are still debating over which came first, the nucleic acids or the proteins.
Recent experiments on the revised atmospheric conditions have been successful in producing the usual monomers and a few that were not formed in the Miller-Urey experiment.
The mass action law suggests that polymerization is not likely to have occurred in the sea, but more likely to have occurred in heated and highly concentrated pools of monomers. Treating amino acids in this manner, Sydney Fox produced polymers that aggregated into what he called proteinoids.
THE BIG BANG First proposed by George Lemaître in 1927 Salient Features
Our Universe began as an infinitesimally small, infinitely hot, infinitely dense singularity.
Then it inflated (big bang), expanded and cooled to the size and temperature of our present Universe.
Timeline of the Big Bang
What happened after the Big Bang?
Evidences for the Big Bang
Galaxies are moving away from us at speeds proportional to their distance. This is called "Hubble's Law," named after Edwin Hubble (1889-1953) who discovered this phenomenon in 1929
The abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins
Cosmic Background Radiation predicted by Cosmologist George Gamov in 1948 and discovered by Arno Penzias & Robert Wilson of Bell Labs in 1965.
THE COMPETITORS … FOR THE THEORY ON ORIGIN OF THE UNIVERSE
The Bubble Universe / Andre Linde's Self Creating Universe
The Inflationary Theory (1981, Alan Guth )
The Protouniverse (white hole theory)
The Steady State Theory (late 1940’s )
The Oscillating Universe Theory (1960’s -70’s )
References
The Cosmos by Carl Sagan
Text Book of Biology by Campbell
The Scientific American
http://scienceweek.com
www.nationalgeographic.com
Humphris, Susan E. and Tom McCollom. “The Cauldron Beneath the Seafloor,” Oceanus, Vol. 41, No. 2, 1998, 18.
Sawyer, Kathy. “Signs of Earliest Life in Ocean Depths—Scalding Habitat May Have Supported Microbes, Fossils Indicate,” Washington Post, June 8, 2000.
Nobody understands the origin of life. If they say they do, they are probably trying to fool you. — Ken Nealson, 2002
THANK YOU
The facts……. hidden somewhere
The story….….. unrevealed
The truth….. not known exactly
The path…. untraced
An attempt to explore the way!!!
An effort to blend biology, chemistry, and physics in the search to identify and understand the origin of life in the universe
It’s a “Journey Back In Time”…
By Kalpana Stuti, Ritu, Gauri
Miranda House
ORIGIN OF LIFE
BIG BANG
Cosmic dust and gases+ H2O
Oceans
Haldane soup
Reducing atmosphere(gases like CH4,NH3,N2,CO2,H2O responsible for abiotic synthesis of organic compounds)
OPARIN-HALDANE THEORY
Haldane Soup
Simple Molecules
Complex Molecules (building blocks)
Aggregates (coacervates and microspheres)
Protocells( proprimitive stage before formation of true cell
Proto cells + nucleic acid = self replicating system
“CELL”
Microsphere
ENERGY YIELDING SYSTEM
“Cell”
Energy Yielding System
Chlorophyll development
Photosynthesis
O2 evolved
Ozone Formation (shielding effect)
Atmosphere changed to oxidizing from reducing.
Evolution of photosynthesis which is followed by respiration.
CELL
Replication
Metabolism
Homeostasis
Anaerobes
Aerobes
Chemotrophs
Heterotrophs
Chemoheterotrophs
Chemoautotrophs
Prokaryotic Cells
Eukaryotic cell
Endosymbiotic Theory
How Eukaryotic Cell Changed to Multicellular Organism….
EVIDENCES???
Geological Evidence
Precambrian Fossil Evidence
Laboratory Evidence
GEOLOGICAL EVIDENCE
Sedimentary rock in past 500 million years are silicate sands clay, quartz type indicating oxidizing conditions.
Ancient Precambrian sediments containing sands with reduced iron minerals found in Canada, Brazil, South Africa.
Banded iron ore deposits with mixed oxidation states in Quinland, Russia, India and Australia
PRECAMBRIAN FOSSIL EVIDENCE
Elso Barghoorn et al studied polished thin sections of silica rich cherts from Gunflint region of Northern Minnesota and Southern Canada with optical and electron microscope.
Living organisms algae, fungi, microbes associated with banded iron ore cherts indicates that they were probably laid down under reducing atmospheric conditions.
LABORATORY EVIDENCE MILLER & UREY EXPERIMENT
A mixture of H4,NH3, H2, and water was put into a flask and energized by an electrical discharge apparatus to represent ultraviolet radiation .
The products were allowed to condense and collect in a lower flask.
. After a week, Miller and Urey found a dark brown scum had collected in the lower flask and was found to contain several types of amino acids together with sugars, tars, and various other unidentified organic chemicals.
How could polymer form in dilute aqueous solution when polymerization is a dehydration process?
Sidney Fox experiment – Fox found that dry amino acids heated to 160-210OC, forms polymers of molecular weight 300,000 provided mixture contains Aspartic Acid and Glutamic Acid. Thermal protenoids so formed, if washed with water, form microspheres of fairly uniform diameter of 20, 000Ao
Cinder Cone Hypothesis - Protenoid material first polymerized on hot dry volcanic Cinder Cones and then it was leached into oceans by rains to form microspheres.
These became early segregated chemical systems and eventually led to protocells.
COACERVATES
They tend to concentrate some molecules in their interior and this in an ability that most primitive protocells would have acquired. Behavior of Coacervate shows how earlier protocells would have achieved internal compositions that were different from their surroundings and could have developed certain amount of chemical evidences.
Coacervate droplets formed by interaction between gelatin and gum arabic. A. I. Oparin
Amylase
Sunlight
Ascorbic Acid + Dye
Chloroplast e- + Dye
Reduced Dye (colour change)
Amylase
Starch
Maltose
PANSPERMIA THEORY
Organic compounds arrived from outer space
It states that hydrocarbons and other organic molecules (molecules that organisms contain or that might lead to the genesis of life) have been found in meteorites –
It means that at least prebiotic chemistry that leads to the primordial soup might be going on there.
Evidences in support of this theory
In 1969, a meteorite landed in Australia that was 12% water and contained traces of 92 amino acids.
Inference- It points to not only the presence of organic compounds in outer space, but also the capacity of such compounds to reach earth.
Fred Hoyle and Chandra Wickramasinghe have argued persistently since the 1970s that complex organic substances, and perhaps even primitive organisms, might have evolved on the surface of comic dust grains in space and then been transported to the Earth's surface by comets and meteorites.
Where did life begin???
There is an ongoing debate regarding the most probable site of life's origins.
The prevailing paradigm - life began near the ocean's surface, bathed in sunlight.
Current Research - life arose near deep hydrothermal vents which is still under investigation.
"Scientists have long suspected that life on Earth originated in the ocean and strong evidence now suggests that the earliest life on our planet occurred in the depths of the ocean in the absence of heat and light."
-- Pulse of the Planet, American Museum of Natural History
Miller and Urey found
Photograph from National Geographic magazine
Deep-sea Vents
Their discovery in late 1970’s stretched our concept of the origin of life on earth.
Can life exist and that too thousands of meters beneath the surface of sea in absence of sunlight?
It raised the possibility that earlier vents supplied the energy and chemical precursors for origin of protobionts.
Exploring the deep ocean floor
View of the first high-temperature vent (380°C) ever seen by scientists during a dive of the deep-sea submersible Alvin in 1979.
Such geothermal vents are called smokers.
This photograph shows a black smoker, but smokers can also be white, grey, or clear depending on the material being ejected. Photograph by Dudley Foster from RISE expedition
Vent Community
A vent community in its prime: Pale pink eelpout fish and white brachyuran crabs swim and scuttle among blood-red tube worms large and small. Scientists are still trying to figure out how the offspring of such organisms disperse over long stretches of inhospitable seafloor to colonize widely separated vent systems.
Giant Clams
The size of deep-sea giant clams is evident from the hands of a scientist holding them.
(Photograph by William R. Normark, USGS.)
Giant Tube Worms: RIFTIA
On the bottom of the ocean around deep-sea hydrothermal vents, there is a profusion of life that thrives on the hydrogen sulfide (H2S) gas released from the vents.and live inside hard, shell-like protective tubes that attach to the rocks.
Giant tubeworms that live around hydrothermal vents on the sea floor. These creatures are about the size of your hand in shallower waters, but in the ocean's deep they have been found as big as eight feet long!
How they live….
These creatures lack mouths, anuses, intestines and stomachs, and scientists were at a loss to explain how these were getting nutrients to survive and grow.
Their insides are lined with bacteria that oxidize the H2S, turning it into usable nutrients for the worms.
The bacteria, in turn, benefit from the relationship because the worms deliver blood containing hemoglobin which helps the bacteria to break down the sulfides.
They live in a symbiotic relationship with a bacteria that may hold clues as to how life on earth began billions of years ago.
BIOCHEMISTRY AT THE VENTS
H2S
Oxidation by bacteria
Energy released helps in fixing CO2 into small organic molecules
So this cycle ... is the same metabolic pathway that is utilized by plants in photosynthesis ... takes inorganic carbon dioxide and fixes it into organic compounds that are then food. But, the difference here, the critical difference, is that rather than using sunlight, these animals and bacteria are completely independent of sunlight. They utilize chemical energy to power that reaction.
So, ever imagined a life out of toxic Hydrogen Sulphide?!
Released from vents
Chemical of Life - Ammonia, Produced at Vents
Hydrothermal vents were the most likely site for NH3 production where inorganic sulphides acted as catalyst.
N2 +NO2 +N03
Presumed to be present in ancient sea
NH3
FeS, 500oC
89% yield, 15 min
FeO
46% yield 15 min
Powdered Basalt.
20% yield
Stable upto 800oC
RESULTS
Since NH3 cannot survive at temperature above 800oC indicates that nitrogen would have been present only as N2 during early phase of earth’s development.
Life can exist on thermal and chemical energy as opposed to just sunlight as had been thought in the past. And so what was realized is that photosynthesis was not the only way to support life.
What has been discussed so far…
In 1920s, Oparin and Haldane revived the doctrine of spontaneous generation in a more sophisticated form.
In 1953, American chemists Stanley Miller and Urey showed that some amino acids can be chemically produced from NH3 and CH4
in 1970s, Fred Hoyle and Chandra Wickramasinghe rekindled interest in Panspermia. They found evidences, traces of life, in the intervening dust.
In 1980’s the hunt for the most probable site of life’s origin began and then we came to deep sea hydrothermal vents.This discovery stretched our concept of the origin of life on earth.
Scientists are still debating over which came first, the nucleic acids or the proteins.
Recent experiments on the revised atmospheric conditions have been successful in producing the usual monomers and a few that were not formed in the Miller-Urey experiment.
The mass action law suggests that polymerization is not likely to have occurred in the sea, but more likely to have occurred in heated and highly concentrated pools of monomers. Treating amino acids in this manner, Sydney Fox produced polymers that aggregated into what he called proteinoids.
THE BIG BANG First proposed by George Lemaître in 1927 Salient Features
Our Universe began as an infinitesimally small, infinitely hot, infinitely dense singularity.
Then it inflated (big bang), expanded and cooled to the size and temperature of our present Universe.
Timeline of the Big Bang
What happened after the Big Bang?
Evidences for the Big Bang
Galaxies are moving away from us at speeds proportional to their distance. This is called "Hubble's Law," named after Edwin Hubble (1889-1953) who discovered this phenomenon in 1929
The abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins
Cosmic Background Radiation predicted by Cosmologist George Gamov in 1948 and discovered by Arno Penzias & Robert Wilson of Bell Labs in 1965.
THE COMPETITORS … FOR THE THEORY ON ORIGIN OF THE UNIVERSE
The Bubble Universe / Andre Linde's Self Creating Universe
The Inflationary Theory (1981, Alan Guth )
The Protouniverse (white hole theory)
The Steady State Theory (late 1940’s )
The Oscillating Universe Theory (1960’s -70’s )
References
The Cosmos by Carl Sagan
Text Book of Biology by Campbell
The Scientific American
http://scienceweek.com
www.nationalgeographic.com
Humphris, Susan E. and Tom McCollom. “The Cauldron Beneath the Seafloor,” Oceanus, Vol. 41, No. 2, 1998, 18.
Sawyer, Kathy. “Signs of Earliest Life in Ocean Depths—Scalding Habitat May Have Supported Microbes, Fossils Indicate,” Washington Post, June 8, 2000.
Nobody understands the origin of life. If they say they do, they are probably trying to fool you. — Ken Nealson, 2002
THANK YOU
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