Origin of Life

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