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Origin of LifeOrigin of LifeBTY100-Lec#1.1

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Outline

• Understanding LIFE• Origin of Life• Spontaneous Generation and its Examples• Challenging Spontaneous Generation:

Theories

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Understanding LifeWhat is LIFE?The condition that distinguishes animals and

plants from inorganic matter.It includes • the capacity for growth,• reproduction, functional activity, • and continual change preceding death.This study of life and its properties is called……..

Biology

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Understanding biology…..why???

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Have you ever wondered?• What are you made up of?• How your body works? • How do we grow?• Why do we fall ill?• How we react to diseases?• How you resemble or differ from

other people such as your sisters, brothers and parents?

Knowledge of Biology helps us to explore answers of such questions

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Lets check the pitch before we actually start answering all those questions!!!

Lets check the pitch before we actually start answering all those questions!!!

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Origin of Life

The theory of Spontaneous GenerationAlso called AbiogenesisIdea that living things can arise from

nonliving matterIdea lasted almost 2000 yearsConclusions based on untested

observations

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Examples of Spontaneous Generation

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Example #1Observation: Every year in the spring, the Nile

River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times

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Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs.

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Mice came from the moldy grain.Sewage and garbage turned into the rats.

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Challenging Spontaneous Generation

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Francesco Redi’s Experiment (1668)In 1668, Francesco Redi, an Italian

physician, did an experiment with flies and wide-mouth jars containing meat.

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Experimental ProtocolRedi used open & closed flasks which

contained meat. His hypothesis was that rotten meat

does not turn into flies.

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Redi’s (1626-1697) Observations and Evidences

Evidence against spontaneous generation:1. Unsealed – maggots on meat2. Sealed – no maggots on meat3. Gauze – few maggots on gauze, none on meat

He observed these flasks to see in which one(s) maggots would develop.

He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within.

In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.

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Results of Redi’s Experiments

The results of this experiment disproved the idea of spontaneous generation for larger organisms.

but people still thought small organisms bacteria could arise that way.

Redi’s (1626-1697)`Results:

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Challenging Abiogenesis: John Needham

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John Needham (1745)

Showed that microorganisms flourished in various soups that had been exposed to the air.

Claimed that there was a “life force” present in the molecules of all inorganic matter, including air and the oxygen in it, that could cause spontaneous generation to occur

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Needham’s Experiment

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Needham’s ResultsNeedham’s ResultsNeedham’s experiments seemed to

support the idea of spontaneous generation

People didn’t realize bacteria were already present in Needham’s soups

Needham didn’t boil long enough to kill the microbes.

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Lazzaro Spallanzani’s (1765))

He constructed his own experiment by placing broth in each of two separate bottles.

Boiling the broth in both bottles, then sealing one bottle and leaving the other open.

Days later, the unsealed bottle was teeming with small living things that he could observe more clearly with the newly invented microscope.

The sealed bottle showed no signs of life.

Later, he broke the seals & the soups became cloudy with microbes.

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Spallanzani’s Results

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Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force”

Therefore, spontaneous generation remained the theory of the time

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The Theory Finally Changes

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The Final Blow!!

By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize for any experiments that would help resolve this conflict

The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disprove spontaneous generation in microscopic organisms.

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Louis Pasteur (1822-1895)

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Pasteur's Experiment

Hypothesis: Dust particles in the air contains microbes; they are not formed from air itself.

Pasteur put broth into several special S-shaped flasks

Each flask was boiled and placed at various locations.

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Pasteur's Experiment - Step 1

S-shaped Flask (Swan-neck flask)Filled with broth The special shaped was intended

to trap any dust particles containing bacteria

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Pasteur's Experiment - Step 2 Flasks boiled Microbes Killed

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Pasteur's Experiment - Step 3Flask left at various

locations Did not turn cloudyMicrobes not foundNotice the dust that

collected in the neck of the flask

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Pasteur's Experimental Results

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CONCLUSION

• There is something(life form) in the air to which when the broth was exposed, it turned cloudy.

• The broth itself did not convert into microorganisms.

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The Theory of BiogenesisPasteur’s S-shaped flask kept microbes out but

let air in.Proved microbes only come from other

microbes (life from life) - biogenesis

Figure 1.3

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Current Thinking about Origin of Life

• Extra-terrestrial origin: given by Arrhenius• His concept Panspermia hypothesized that life

arose outside the Earth and the living things were transported to earth to seed the planet.

• Chemical evolution: life originated from natural chemical processes which can be observed and evaluated experimentally.

• Inorganic matter->organic matter-> living forms• Role of meteorites

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Origin of life on Earth• Proper temp for water in liquid state.• Earlier Earth lacked oxygen: necessary for

generation of organic molecules.• High atmospheric temperature of early Earth.

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Steps needed to produce life from inorganic molecules

• Organic molecules must be formed from inorganic molecules

• Simple organic molecules must combine to form large organic molecules.

• A molecule must serve as genetic material.• Some molecules must act as enzymes.• Genetic material must be self replicating.• All molecules should be enclosed in a membrane.• Source of energy to survive.

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Formation of first organic molecule

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The Oparin-Haldane theory

1920s: J.B.S. Haldane and Aleksander Oparin independently set forth ideas concerning the conditions required for the origin of life on Earth.

Organic molecules could be formed from abiogenic materials in the presence of an external energy source (e.g., ultraviolet radiation) and primitive atmosphere was reducing (having very low amounts of free oxygen) and contained ammonia and water vapour, among other gases.

First life-forms appeared in the warm, primitive ocean and were heterotrophic.

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REDUCING ATMOSPHERE

• A/o oxygen allowed these organic molecules to remain and combine with each other.

• In present environment the organic molecules are either consumed by organisms or oxidized into simpler inorganic molecules.

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Urey-Miller Experiment1953 American chemists Harold C. Urey and Stanley

Miller tested the Oparin-Haldane theory .Successfully produced organic molecules from some of the

inorganic components thought to have been present on prebiotic Earth.

Combined warm water with a mixture of four gases—water vapour, methane, ammonia, and molecular hydrogen—and pulsed the “atmosphere” with electrical discharges.

The different components were meant to simulate the primitive ocean, the prebiotic atmosphere, and heat (in the form of lightning), respectively.

One week later Miller and Urey found that simple organic molecules, including amino acids (the building blocks of proteins), had formed under the simulated conditions of early Earth.

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First Life forms

• Prebionts: Non living structures that led to first living cells.

• Formed of proteins, carbohydrates, lipids and Nucleic acids.

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Towards Complexity

• Additional steps required:• Proteins must become catalysts of cells• Development of genetic material• Must have away to obtain energy.

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Next Class:Evolution