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Origin of Life

Origin of Life. Chapter 14. Biogenesis vs. Spontaneous Generation. Biogenesis States that all living things come from other living things Spontaneous generation Early, now disproved, hypothesis that living organisms develop from nonliving material. Francesco Redi’s.

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Origin of Life

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  1. Origin of Life Chapter 14

  2. Biogenesis vs. Spontaneous Generation • Biogenesis • States that all living things come from other living things • Spontaneous generation • Early, now disproved, hypothesis that living organisms develop from nonliving material

  3. Francesco Redi’s • Middle of 17th century, Italian scientist Francesco Redi described different developmental forms of flies

  4. Redi’s Experiment • Belief: Maggots come from rotting meat • Redi’s 1668 Hypothesis: Maggots come from flies • Redi put meat in 3 separate jars • Jar 1: Left open • Jar 2: Covered with netting • Jar 3: Sealed from outside

  5. Left open Maggots developed Flies were observed laying eggs on the meat in the open jar Redi’s Experiment Step 1

  6. Covered with netting Maggots appeared on the netting Flies were observed laying eggs on the netting Redi’s Experiment Step 2

  7. Sealed No maggots developed Redi’s Experiment Step 3

  8. Redi’s Conclusions • Experiment showed convincingly that flies come only from eggs laid by other flies • 1st major blow towards idea of spontaneous generation

  9. Lazzaro Spallanzani • Italian scientist • In 1700s, designed experiment to test hypothesis of spontaneous generation of microorganisms • Spallanzani benefited from the invention of the microscope

  10. Spallanzani’s Experiment • Belief: Microorganisms came from the air • Hypothesis: Microorganisms came from other microorganisms. Boiling will kill the microorganisms. • Used meat broth to test his hypothesis • Spallanzani put broth into four flasks • Flask 1 was left open • Flask 2 was sealed • Flask 3 was boiled and then left open • Flask 4 was boiled and then sealed

  11. Left Open Turned cloudy Microbes were found Spallanzani's Experiment Step 1

  12. Sealed Turned cloudy Microbes were found Spallanzani's Experiment Step 2

  13. Boiled and left open Turned cloudy Microbes were found Spallanzani's Experiment Step 3

  14. Boiled and sealed Did not turn cloudy Microbes not found Spallanzani's Experiment Step 4

  15. Spallanzani’s Conclusions • Boiled broth became contaminated only when microorganisms from the air entered the flask • Opponents: Claimed Spallanzani heated experimental flasks too long, destroying the “vital force” in air inside them • Air lacking “vital force” could not generate life

  16. Louis Pasteur • French scientist • Developed experiment in mid-1800s that ended the controversy of Spallanzani’s experiment • Used special curved-shaped flasks

  17. Pasteur’s Experiment • Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself • Each flask was boiled and placed at various locations

  18. Filled with broth The special shaped was intended to trap any dust particles coming in Pasteur's Experiment Step 1

  19. Flasks boiled Microbes killed Pasteur's Experiment Step 2

  20. Flask left at various locations Did not turn cloudy Microbes not found Pasteur's Experiment Step 3

  21. Dust collected in the neck of the flask & prevented microorganisms from entering body of the flask Pasteur's Experiment Step 4

  22. Pasteur’s Conclusions • Experimental curve-necked flasks remained clear for up to a year • Once Pasteur broke off curved necks, broth became cloudy & contaminated with microorganisms within a day • Pasteur reasoned contamination was due to microorganisms in the air • Pasteur’s conclusions allowed the principle of biogenesis to become the cornerstone of biology

  23. Formation of the Earth • Solar system formed approximately 5 billion years ago • Began as a swirling mass of gas & dust • Over time, most of the material collapsed inward, forming sun • Left over material circled the young sun • Collisions between this left over debris formed the planets

  24. Earth’s Age • Estimated age of Earth is 4 billion years old • Scientists have created a geologic history of the earth by examining the layers of sediment • Early estimates were simply based on studying the sediment layers • Around mid-twentieth century, radioactive dating methods were implemented

  25. Radioactive Dating • Age of a material can be determined by measuring the amount of a particular radioactive isotope it contains • Compare this quantity with the amount of some other substance in the that remains constant over time

  26. Background Info for Radioactive Dating • Recall, all atoms of an element have the same atomic number, but their number of neutrons can vary • Isotopes are atoms of the same element that differ in the number of neutrons they contain • Mass number refers to the total number of protons & neutrons • Isotopes are designated by their chemical name followed by their mass number • Carbon-12; carbon-14

  27. Background Info for Radioactive Dating • Some isotopes, radioactive isotopes, have unstable nuclei—which undergo radioactive decay • Half-life refers to the length of time it takes for one-half of any size sample of an isotope to decay • Length depends on isotope & can vary from fraction of a second to billions of years

  28. Carbon-14 Dating • Limited to organic remains less than ~60,000 years old • Amount of carbon-14 (radioactive isotope) is compared to the amount of carbon-12 (stable isotope) • Living things take carbon into their bodies constantly, mostly in the form of carbon-12 but some in the form of carbon-14 • When an organism dies, the intake of carbon ceases • Over time, amount of carbon-14 declines with respect to amount of carbon-14 • Half-life of carbon-14 is 5,730 years

  29. Other Methods of Radioactive Dating • Earth’s age has by estimated using the decay of uranium & thorium in rock crystals • Half-life of thorium-230 is 75,000 years • Half-life of uranium-238 is 4,500,000,000 years

  30. The 1st Organic Compounds • All elements found in organic compounds are thought to have existed on Earth & rest of solar system when Earth formed • The question then is how & where these elements assembled into the organic compounds found in life?

  31. Oparin’s Hypothesis • In 1923, Alexander I. Oparin, a Soviet scientist, suggested that the atmosphere of the primitive Earth was very different from that of today • Early atmosphere was thought to contain ammonia, hydrogen gas, water vapor, & methane

  32. Oparin’s Hypothesis • Temperatures above the boiling point of water could allow these gases to form simple organic compounds—like amino acids • As the Earth cooled & water vapor condensed, lakes & seas formed • Lakes & seas were a collection ground for the simple organic compounds • Over time, these simple compounds could have entered complex chemical reactions caused by lightening & UV radiation • Thus resulting in the macromolecules essential to life—like proteins

  33. Miller-Urey Experiment • Oparin never tested his hypothesis • In 1953, Stanley Miller & Harold Urey set up an experiment to test Oparin’s hypothesis • Apparatus included a chamber containing the gases Oparin assumed were present in the young Earth’s atmosphere • Electric sparks substituted the lightening to supply the energy necessary to drive chemical reactions • Experiment produced a variety of organic compounds—amino acids, ATP, nucleotides in DNA

  34. New Hypothesis • Early atmosphere of Earth was composed largely of carbon dioxide, nitrogen, & water vapor • Both carbon dioxide & oxygen interfere with production or organic compounds • Believed that areas like undersea hot springs, favored the production of organic compounds since they are protected from the atmosphere

  35. Organic Compounds from Beyond Earth • A newly fallen meteorite that was recovered before it was contaminated, was found to contain a broad mixture of organic compounds • Speculation that that life on Earth began in space and was carried here by space debris rather than originating here on Earth

  36. From Molecules to Cell-Like Structures • Sidney Fox’s research • Cell-like structures form spontaneously in laboratory from solutions of simple organic chemicals • Structures include… • 1). Microspheres • Spherical in shape, composed of many protein molecules, & are organized as a membrane • 2). Coacervates • Collections of droplets composed of molecules of different types—amino acids & sugars

  37. Coacervates & Microspheres • Have many life-like properties • Ability to take up certain substances from their surroundings • Coacervates can grow • Microsphres can bud to form smaller microspheres • Show that some important aspects of cellular life arose without direction from genes

  38. The 1st Life Forms • Oldest known cellular fossils were found in a desolate corner of Australia • The unicellular organisms were 3.5 billion years old

  39. Origin of Heredity • Recall… • DNA is transcribed to form mRNA • tRNA translates the 3-base codons, amino acids, into mRNA • RNA message is then translated into a protein

  40. Origin of Heredity • Question arose—why is RNA necessary to carry out protein synthesis? • Understanding function of RNA can be found in its shape • Can take on variety of shapes • Shapes are controlled by hydrogen bonds • Might behave like proteins & catalyze chemical reactions

  41. Roles of RNA • Early 1980s, researcher Thomas Cech found RNA found in some unicellular eukaryotes can act as an enzyme • Called it a ribozyme • RNA molecule that can act as an enzyme & promote a specific chemical reaction, but still has the ability to replicate

  42. Roles of RNA • Recent studies suggest life started with self-replicating molecules of RNA • RNA has hereditary information • RNA would be able to respond to natural selection & thus evolve • Also found that RNA plays a vital role in DNA replication, protein synthesis, RNA processing • Still many unanswered questions • Have not discovered ribozyme that can self-replicate

  43. 1st Prokaryotes • Characteristics of first cellular life • Anaerobic—little or no oxygen in existence • Heterotrophic—took in organic molecules from environment • Eventually resources depleted, push for organisms to evolve

  44. Chemosynthesis • Archaebacteria • Unicellular organisms • Thrive under harsh environmental conditions • Many are autotrophic, but obtain energy by chemosynthesis • In chemosynthesis, CO2, serves as carbon source for assembly of organic molecules

  45. Photosynthesis & Aerobic Respiration • Oxygen is a byproduct of photosynthesis • Oxygen destroyed coenzymes essential to cell function of early unicellular organisms • Some organisms were not damaged--bind the oxygen—aerobic respiration • Photosynthetic life formed by 3 billion years ago

  46. Photosynthesis & Aerobic Respiration • Took billion years or more for oxygen levels to reach today’s levels • Eventually reached upper atmosphere & formed ozone • Layer absorbs UV radiation from sun • UV radiation damages DNA

  47. 1st Eukaryotes • Differences between Prokaryotes & Eukaryotes • Eukaryotic cells are larger • Eukaryotes DNA is organized into chromosomes in a nucleus • Eukaryotes contain membrane bound organelles

  48. 1st Eukaryotes • How did eukaryotes evolve from prokaryotes? • Evidence that between 2 & 1.5 billion years ago, small aerobic prokaryote entered & began to live & reproduce inside larger anaerobic prokaryote • Endosymbiosis—mutually beneficial relationship • Believed that aerobic prokaryote gave rise to modern mitochondria

  49. 1st Eukaryotes • Another later invasion, gave rise to chloroplasts • Sites of photosynthesis • Both chloroplasts & mitochondria… • Replicate independently from replication cycle of cell • Contain some of their own genes

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