Origin of life with turning point qs
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  • Life is defined by two properties: accurate replication and metabolism. Neither property can exist without the other. DNA molecules carry genetic information, including the information needed for accurate replication. The replication of DNA requires elaborate enzymatic machinery, along with a copious supply of nucleotide building blocks provided by cell metabolism. Although Miller-Urey experiments have yielded some of the nitrogenous bases of DNA and RNA, they have not produced anything like nucleotides. Thus, nucleotides were likely not part of the early organic soup. Self-replicating molecules and a metabolism-like source of the building blocks must have appeared together. The necessary conditions may have been provided by protobionts , aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure. Protobionts exhibit some of the properties associated with life, including reproduction and metabolism, and can maintain an internal chemical environment different from their surroundings.
  • Laboratory experiments show the spontaneous formation of protobionts from abiotically produced organic compounds. For example, droplets of abiotically produced organic compounds called liposomes form when lipids and other organic molecules are added to water. The hydrophobic molecules in the mixture form a bilayer at the droplet surface, much like the lipid bilayer of a membrane. Because the liposome bilayer is selectively permeable, liposomes undergo osmotic swelling or shrinking in different salt concentrations. Some liposomes can perform simple metabolic reactions.
  • The first genetic material was probably RNA, not DNA. Thomas Cech and Sidney Altman found that RNA molecules not only play a central role in protein synthesis but also are important catalysts in modern cells.
  • Laboratory experiments have demonstrated that RNA sequences can evolve under abiotic conditions. Unlike double-stranded DNA, single-stranded RNA molecules can assume a variety of three-dimensional shapes specified by their nucleotide sequences. RNA molecules have both a genotype (nucleotide sequence) and a phenotype (three-dimensional shape) that interact with surrounding molecules. Under particular conditions, some RNA sequences are more stable and replicate faster and with fewer errors than other sequences.
  • RNA catalysts, called ribozymes, can make complementary copies of short pieces of RNA when supplied with nucleotide building blocks.
  • Modern molecular biology may have been preceded by an “RNA world,” in which small RNA molecules that carried genetic information replicated and stored information about the protobionts that carried them. A protobiont with self-replicating, catalytic RNA would differ from others without RNA or with RNA that had fewer capabilities. If that protobiont could grow, split, and pass on its RNA molecules to its daughters, the daughters would have some of the properties of their parent.
  • The first protobionts must have had limited amounts of genetic information, specifying only a few properties. Because their properties were heritable, they could be acted on by natural selection. The most successful of these protobionts would have increased in numbers because they could exploit available resources and produce similar daughter protobionts. Once RNA sequences that carried genetic information appeared in protobionts, many further changes were possible.
  • One refinement was the replacement of RNA as the repository of genetic information by DNA. Double-stranded DNA is a more stable molecule, and it can be replicated more accurately. Once DNA appeared, RNA molecules began to take on their modern roles as intermediates in the translation of genetic programs. The “RNA world” gave way to a “DNA world.”

Origin of life with turning point qs Origin of life with turning point qs Presentation 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
  • Spontaneous Generation
    • 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
  • 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
  • Example #1
      • Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs
  • Example #2
    • 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 .
  • Example #2
      • Conclusion: It was obvious to them that the mice came from the moldy grain.
  • Example #3
    • 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 .
  • Example #3
      • Conclusion: Obviously, all the sewage and garbage turned into the rats .
  • Example #4
    • 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.
  • Example #4
      • Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies .
  • Abiogenesis Recipes
    • 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.
  • Abiogenesis Recipes
    • 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’s Experiment
    • 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.
  • Redi’s Findings
    • 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.
  • Francesco Redi
  • Did Redi Use the Scientific Method?
  • The Scientific Method
    • Observation
    • Hypothesis
    • Experiment
    • 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
  • Leeuwenhoek’s Microscope
  • 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 Results
    • 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
  • Needham’s Experiment
  • 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.
  • Spallanzani’s Results
  • Conclusion
    • 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)
  • Pasteur's Problem
    • 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
    • S-shaped Flask
    • Filled with broth
    • The special shaped flask was intended to trap any dust particles containing bacteria
  • Pasteur's Experiment - Step 2
    • Flasks boiled
    • Microbes Killed
  • 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
  • Review
    • 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?
    • Early Earth
  • 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.
  • Radioactive Decay
  • 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.
  • Miller-Urey Experiment
  • Lerman’s Bubble Model
  • Early Life on Earth
  • Protobionts
    • Aggregates of abiotically produced molecules.
    • Exhibit some properties of life.
      • Ex: Osmosis, Electrical Charge, Fission
  • Protobionts
  • Protobiont Formation
    • Proteinoids + H 2 O  microspheres
    • Liposomes + H 2 O  lipid membranes
  • Coacervates
    • Colloidal droplets of proteins, nucleic acids and sugars surround by a water shell.
    • Will form spontaneously from abiotically produced organic compounds.
  • Summary
    • Protobionts have membrane-like properties and are very similar to primitive cells.
    • Start for selection process that lead to cells?
  • Question ?
    • Where did the energy come from to run these early cells?
  • Answer
    • ATP.
    • Reduction of sulfur compounds.
    • Fermentation.
    • Rs and Ps developed much later.
  • Genetic Information
    • DNA  RNA  Protein
    • Too complex for early life.
    • Other forms of genetic information?
  • RNA Hypothesis
    • RNA as early genetic information.
  • Rationale
    • RNA polymerizes easily.
    • RNA can replicate itself.
    • RNA can catalyze reactions including protein synthesis.
  • Ribozymes
    • RNA catalysts found in modern cells.
      • e.g. ribosomes
    • Possible relic from early evolution?
  • Molecular Cooperation
    • Interaction between RNA and the proteins it made.
    • Proteins formed may serve as RNA replication enzymes.
  • Molecular Cooperation
    • Works best inside a membrane.
    • RNA benefits from the proteins it made.
  • Selection favored:
    • 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
    • How new life started
    • How simple organic molecules formed
    • How microspheres formed
    • How eukaryotes evolved
    20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
  • Redi’s experiment was important because it showed that
    • Maggots give rise to microorganisms
    • Flies swarm on rotting meat
    • Flies do not form from rotting meat
    • Air contains a “vital force”
    20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
  • People objected to Spallanzani’s experiment because he
    • Used an open jar of meat as a control
    • Boiled his flasks of broth for a long time
    • Drew the necks of his flasks into a long shape
    • Did not have a control group
    10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
  • The neck of Pasteur’s flasks
    • Allowed both air and particles to enter the flask
    • Allowed air but not particles in
    • Allowed particles in but not air
    • Kept both air and particles out
    20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
  • The oldest fossil of cellular life on Earth is
    • About 4.6 billion years old
    • About 4.2 billion years old
    • About 3.5 billion years old
    • Less than 2 billion years old
    20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
  • Coacervates and microspheres cannot evolve because they have no
    • Genetic information
    • Cell membrane
    • Complex organic molecules
    • Fluid in their interior
    20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
  • Miller and Urey’s experiment
    • Proved Oparin’s hypothesis about the origin of organic molecules
    • Disproved Oparin’s hypotheisi
    • Provided support for Oparin’s hypothesis
    • Is irrelevant to any hypothesis regarding the origin of life
    20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30