Origin of Life The theory of spontaneous generation The theory of spontaneous generation Also called abiogenesis Also called abiogenesis Idea that living things can arise from nonliving matter Idea that living things can arise from nonliving matter Idea lasted almost 2000 years Idea lasted almost 2000 years Conclusions based on untested observations Conclusions based on untested observations

Examples of Spontaneous Generation

Example #1 Observation: 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 Observation: 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

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

Mice came from the moldy grain.

Sewage and garbage turned into the rats Sewage and garbage turned into the rats.

Challenging Spontaneous Generation

Francesco Redi (1668) In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide- mouth jars containing meat In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide- mouth jars containing meat

Redi’s Experiment Redi used open & closed flasks which contained meat. Redi used open & closed flasks which contained meat. His hypothesis was that rotten meat does not turn into flies. His hypothesis was that rotten meat does not turn into flies. He observed these flasks to see in which one(s) maggots would develop. 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. 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. 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.

Redi’s ( ) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat

Results of Redi’s Experiments The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way. The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way.

Francesco Redi

Disproving Spontaneous Generation of Microbes

John Needham (1745) Showed that microorganisms flourished in various soups that had been exposed to the air 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 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

Needham’s Results Needham’s experiments seemed to support the idea of spontaneous generation Needham’s experiments seemed to support the idea of spontaneous generation People didn’t realize bacteria were already present in Needham’s soups People didn’t realize bacteria were already present in Needham’s soups Needham didn’t boil long enough to kill the microbes Needham didn’t boil long enough to kill the microbes

Needham’s Experiment

Lazzaro Spallanzani’s (1765) Boiled soups for almost an hour and sealed containers by melting the slender necks closed Boiled soups for almost an hour and sealed containers by melting the slender necks closed. The soups remained clear. The soups remained clear. Later, he broke the seals & the soups became cloudy with microbes. Later, he broke the seals & the soups became cloudy with microbes.

Spallanzani’s Results

Conclusion Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force” 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 Therefore, spontaneous generation remained the theory of the time

The Theory Finally Changes

How Do Microbes Arise? 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 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 disproved spontaneous generation in microscopic organisms The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disproved spontaneous generation in microscopic organisms

Louis Pasteur ( )

Pasteur's Problem Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself. Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself. Pasteur put broth into several special S-shaped flasks Pasteur put broth into several special S-shaped flasks Each flask was boiled and placed at various locations Each flask was boiled and placed at various locations

Pasteur's Experiment - Step 1 S-shaped Flask S-shaped Flask Filled with broth Filled with broth The special shaped was intended to trap any dust particles containing bacteria The special shaped was intended to trap any dust particles containing bacteria

Pasteur's Experiment - Step 2 Flasks boiled Flasks boiled Microbes Killed Microbes Killed

Pasteur's Experiment - Step 3 Flask left at various locations Flask left at various locations Did not turn cloudy Did not turn cloudy Microbes not found Microbes not found Notice the dust that collected in the neck of the flask Notice the dust that collected in the neck of the flask

Pasteur's Experimental Results

The Theory of Biogenesis Pasteur’s S-shaped flask kept microbes out but let air in. Pasteur’s S-shaped flask kept microbes out but let air in. Proved microbes only come from other microbes (life from life) - biogenesis Proved microbes only come from other microbes (life from life) - biogenesis Figure 1.3

Current Thinking about Origin of Life Extra-terrestrial origin: Arrhenius Panspermia Did not explain how life originated. Chemical evolution: life originated from natural chemical processes which can be observed and evaluated experimentally. Inorganic matter->organic matter-> living forms Role of meteorites

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.

The “Big Bang” and Origin of Earth Universe began as a very dense mass of matter. Exploded in a big bang about 13 billion years ago. Original Universe consisted of atoms of H and He. Gravitation led to formation of stars and solar system Earth formed about 4.6 billion years ago: Hadean Eon (Hellish!!!) Reducing Environment: no Oxygen was present initially. Cooling led to condensation.

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 me enclosed in a membrane. Source of energy to survive.

Formation of first organic molecule

The Oparin-Haldane theory 1920s: J.B.S. Haldane and Aleksandr 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.

Physico-chemical changes Chemical evolution A) Formation of inorganic molecules and compounds B) Formation of simple organic compounds Biological evolution A) origin of aggregates of complex organic molecules capable of growth and division (Coacervates: Large colloidal aggregates in ocean) B) Protobionts and Eubionts (Protocells) C) Prokaryotes D) Eukaryotes

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.

Urey-Miller Experiment 1953 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.

hill.com/sites/ /student_view0/chapter26/ animation_-_miller-urey_experiment.html hill.com/sites/ /student_view0/chapter26/ animation_-_miller-urey_experiment.html

Formation of Macromolecules Dehydration synthesis: evaporation led to concentration. Freezing as a means of concentration Role of electrically charged clay particles that attract and concentrate molecules.

Origin of Genetic Material RNA could have been the first genetic material Evidence Can make copies of itself Can act as enzyme Much simpler than DNA Mutates quickly

First Life forms Prebionts: Non living structures that led to first living cells. Formed of proteins, carbohydrates, lipids and Nucleic acids. Interacted to form Coacervates: Structure that could have consisted of a collection of organic molecules surrounded by a film of water molecules (barrier).

Microsphere: early prebiotic cell structure A non living collection of organic molecules with a double layered boundary Formed from proteinoids. Donot contain lipids in membrane but they exhibit membrane like characters eg. Response to osmotic potential, streaming, can use ATP to form NAs and Polypeptides. Absorb materials from surroundings and form buds

Membrane could form with lipids interacting with water. Separation of organic molecules from primordial soup led to protocells

Towards Complexity Additional steps required: Proteins must become catalysts of cells Control of protein synthesis must be taken over by RNA DNA must replace RNA as genetic material First cellular units must be able to reproduce Must have away to obtain energy.

Quiz First living organisms could have been??? Heterotrophs Autotrophs

Major Evolutionary changes Development of oxidizing atmosphere Establishment of three domains of life Origin of Eukaryotic cell: Endosymbiotic theory