Origin of life with turning point qsPresentation Transcript
Origin of Life
Aristotle (384 –322 BC)
Proposed the theory of spontaneous generation
Also called abiogenesis
Idea that living things can arise from nonliving matter
Idea lasted almost 2000 years
For centuries , people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas
They didn’t use the scientific method to arrive at answers to their questions
Their conclusions were based on untested observations
Examples of Spontaneous Generation
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
Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain , and of course there were lots of mice around .
Conclusion: It was obvious to them that the mice came from the moldy grain.
Observation: In the cities centuries ago, there were no sewers, no garbage trucks, no electricity, and no refrigeration. Sewage flowed down the streets, and chamber pots and left over food were thrown out into the streets each morning. Many cities also had major rat problems and a disease called Bubonic plague .
Conclusion: Obviously, all the sewage and garbage turned into the rats .
Observation: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses . Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them.
Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies .
Recipe for bees:
Kill a young bull , and bury it in an upright position so that its horns protrude from the ground . After a month, a swarm of bees will fly out of the corpse.
Recipe for mice:
Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days , mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.
Disproving Spontaneous Generation
Francesco Redi (1668)
In 1668, Francesco Redi , an Italian physician, did an experiment with flies and wide-mouth jars containing meat
Redi used open & closed flasks which contained meat .
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 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.
Redi’s (1626-1697) 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.
Did Redi Use the Scientific Method?
The Scientific Method
Accept, Reject, or Modify hypothesis
Step 1 - Observation
There were flies around meat carcasses at the Butcher shop.
Where do the flies come from?
Does rotting meat turn into or produce rotting flies?
Step 2 - Hypothesis
Rotten meat does not turn into flies. Only flies can make more flies.
Step 3 - Testing
Wide-mouth jars each containing a piece of meat were subjected to several variations of “openness” while all other variables were kept the same.
Control group — These jars of meat were set out without lids so the meat would be exposed to whatever it might be in the butcher shop.
Experimental group(s) — One group of jars were sealed with lids, and another group of jars had gauze placed over them.
Step 4 - Data
Presence or absence of flies and maggots observed in each jar was recorded .
Control group – flies entered, laid eggs, & maggots emerged
Gauze covered – flies on gauze, but not in jar
Sealed jars – No maggots or flies on the meat
Step 5 - Conclusion
Only flies can make more flies . In the uncovered jars , flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggots from them dropped through the gauze onto the meat. In the sealed jars , no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms.
Disproving Spontaneous Generation of Microbes
Anton van Leeuwenhoek (1674)
Leeuwenhoek began making and looking through simple microscopes
He often made a new microscope for each specimen
He examined water and visualized tiny animals, fungi, algae, and single celled protozoa; “animalcules”
By end of 19 th century, these organisms were called microbes
Anton van Leeuwenhoek 1632-1723
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
Needham’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
Lazzaro Spallanzani’s (1765)
Boiled soups for almost an hour and sealed containers by melting the slender necks closed .
The soups remained clear .
Later, he broke the seals & the soups became cloudy with microbes.
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
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
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 (1822-1895)
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
Each flask was boiled and placed at various locations
Pasteur's Experiment - Step 1
Filled with broth
The special shaped flask was intended to trap any dust particles containing bacteria
Pasteur's Experiment - Step 2
Pasteur's Experiment - Step 3
Flask left at various locations
Did not turn cloudy
Microbes not found
Notice the dust that collected in the neck of the flask
Pasteur's Experimental Results
Pasteur’s S-shaped flask kept microbes out but let air in .
Proved microbes only come from other microbes (life from life) - biogenesis
The Theory of Biogenesis Figure 1.3
1668: Francisco Redi filled six jars with decaying meat.
Evidence Pro and Con Conditions: Results: 3 jars covered with fine net No maggots 3 open jars Maggots appeared From where did the maggots come? What was the purpose of the sealed jars? S pontaneous generation or biogenesis?
1745: John Needham put boiled nutrient broth into covered flasks.
Evidence Pro and Con Conditions: Results: Nutrient broth heated, then placed in sealed flask Microbial growth From where did the microbes come? S pontaneous generation or biogenesis?
1765: Lazzaro Spallanzani boiled nutrient solutions in flasks.
Evidence Pro and Con Conditions: Results: Nutrient broth placed in flask, heated, then sealed No microbial growth S pontaneous generation or biogenesis?
1861: Louis Pasteur demonstrated that microorganisms are present in the air.
Evidence Pro and Con Conditions: Results: Nutrient broth placed in flask, heated, not sealed Microbial growth Nutrient broth placed in flask, heated, then sealed No microbial growth S pontaneous generation or biogenesis?
Age of the Earth
The Earth began as a collection of cosmic dust 4.5 billion years ago.
Radiometric dating allows us to compare amounts of radioactive isotopes and their stable daughter products to determine age
A half-life is the time required for half a radioactive isotope to degrade.
Early Organic Molecules
Oparin and Haldane suggested the primordial soup model.
Miller-Urey conducted experiments to create organic molecules in the early atmosphere.
The Bubble model suggests: gases were trapped in bubbles. Gases went through chemical reactions and released to atmosphere to react like Miller-Urey and fell into the ocean.
Lerman’s Bubble Model
Early Life on Earth
Aggregates of abiotically produced molecules.
Exhibit some properties of life.
Ex: Osmosis, Electrical Charge, Fission
Proteinoids + H 2 O microspheres
Liposomes + H 2 O lipid membranes
Colloidal droplets of proteins, nucleic acids and sugars surround by a water shell.
Will form spontaneously from abiotically produced organic compounds.
Protobionts have membrane-like properties and are very similar to primitive cells.
Start for selection process that lead to cells?
Where did the energy come from to run these early cells?
Reduction of sulfur compounds.
Rs and Ps developed much later.
DNA RNA Protein
Too complex for early life.
Other forms of genetic information?
RNA as early genetic information.
RNA polymerizes easily.
RNA can replicate itself.
RNA can catalyze reactions including protein synthesis.
RNA catalysts found in modern cells.
Possible relic from early evolution?
Interaction between RNA and the proteins it made.
Proteins formed may serve as RNA replication enzymes.
Works best inside a membrane.
RNA benefits from the proteins it made.
RNA/protein complexes inside membranes as they were the most likely to survive and reproduce.
DNA Developed later as the genetic information
Why? More stable than RNA
The hypothesis of spontaneous generation was used to explain