Origin of Life

1. Origin of Life Ms. Pelullo 2013

2. How did life begin?? • Spontaneous Generation (*Abiogenesis): • the idea that life can arise from nonliving material • Examples • mice come from haystacks; • flies come from rotting meat; • bacteria arise from broth • Biogenesis • the idea of life arising from other living organisms • Examples • cats make cats; • humans make humans; • bacteria make bacteria; • plants make plants For thousands of years people believed that living organisms originated from nonliving matter

3. In 1668, Francesco Redi proposed a hypothesis to explain the specific example of maggots that appear on spoiled food. He had observed that maggots appear on meat a few days after flies have been seen on the food. He inferred that the flies had left behind eggs too small to see. Redi’s experiment is shown below. Francesco Redi

4. that flies do not arise from decaying meat (rather, they arise from eggs laid by other flies). What conclusion was drawn from Redi’s experiment?

5. Even though the conclusions of Redi's experiment were clear and easily reproducible, many scientists still believed in the idea of abiogenesis. In the mid-late 1700s… • Experiments by LazzaroSpallanzani further supported the idea that life did not arise spontaneously from food or air. • Scientists knew that heat would kill living organisms -- so Spallanzani boiled broth in flasks and removed air from the flasks, suspecting that the air was providing a source of contamination.

6. After observation of the results and seeing that no living organisms appeared in the flask unless the flask was opened to the air, Spallanzani inferred that some foods spoil because of growing populations of microorganisms - NOT because of spontaneous generation. • Some scientists criticized Spallanzani's experimental findings, insisting that air was necessary for some vital force that would begin life from nonliving organic matter.

7. Spallanzani • Heat • Removal of Air

8. Experiments by Pasteur In the Mid-1800s • He began by passing air through gun cotton filters and inspecting the particles which were isolated. He found that particles floating in air were populated with microorganisms (such as bacteria) and inferred that these particles would likely contaminate any material exposed to it. • He performed an experiment which was similar to Spallanzani's except that he used a specially-shaped swan-neck flask - this special design allowed air to enter the flasks but the curve of the neck trapped any particles floating in air and prevented them from contaminating the boiled broth. • The contents of the boiled flasks remained free of life until he broke off the flask necks and the solutions quickly became filled with a cloudy mixture of microbes. • Flasks which were unboiled showed the same result as the flasks which were opened to the air

9. pASTEUR What was his conclusion? • Bacteria do not spontaneously arise from broth • (rather, it was confirmed that new bacteria only appear when they were produced by existing bacteria).

10. What started it all?!?!? 13.7 billion years ago….

11. So… what happened? • Geologic and astronomical evidence suggests that Earth formed as pieces of cosmic debris collided with one another. While the planet was young, it was struck by one or more huge objects, and the entire globe melted. • An infinitely small, hot dense ‘speck’, inflated, expanded and cooled to the size and temperature of our current universe.

12. Keep going… • For millions of years, violent volcanic activity shook earth's crust. • Comets and asteroids bombarded its surface. • Slowly, heavier elements like iron settled to the interior of the young planet and lighter elements like C, H, and O remained at the surface. • About 4.2 billion years ago, Earth cooled enough to allow solid rocks to form and water to condense and fall as rain.

13. And what else happened? • The rain probably formed from the tremendous amounts of hydrogen and oxygen that escaped from underneath's earth crust. It is thought to have rained for a very long time. Earth's surface (eventually) became stable enough for permanent oceans to form.

14. This infant planet was very different from Earth today. Earth's atmosphere contained little or no oxygen. It was mostly composed of carbon dioxide, water vapor, and nitrogen • Because of the gases in the atmosphere, the sky was probably pinkish-orange and because there was lots of dissolved iron in the oceans, they were probably brown This is the Earth on which life began.

15. Primitive Atmosphere lacked free O2 Abundant Energy for chemical reactions • Early atmosphere contained mostly CO2 and water vapor . Simple organic compounds could remain stable even when exposed to air • Oxygen is a highly reactive compound which tends to break bonds that form between simple organic compounds and destroy them. • Lacking a protective ozone (O3) layer • the atmosphere had abundant UV radiation • Lightning in the atmosphere • Heat from volcanoes above and below ocean level 2 Major Differences between Primitive Earth & Modern Earth

17. OXYGEN

18. Oparin & Haldane Theory of Chemical Evolution

19. Alexander Oparin & J.B. Haldane • Conditions on primitive earth gave rise to simple organic compounds, the precursors to life. • Inorganic Matter like CO2 & NH3, plus organics like CH4 in the atmosphere combined using the energy sources listed previously. • Simple Organic Molecules- Like HCN (hydrogen cyanide) and formaldehyde formed primitive clumps of organic matter. • However they came to be on earth, once organic compounds were present on earth, the stage would be set for the origin of Earth's earliest life forms.

20. In 1953 chemists Miller and Urey tried to answer that question. Could organic molecules assemble under conditions on early Earth?

21. Steps of the Miller-Urey Experiment 1 2 3

22. Steps of the Miller-Urey Experiment 4 5

24. Results of Miller-Urey Experiment • They produced 21 amino acids • The building blocks of proteins. • Miller and Urey's experiment suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds on a primitive earth. • We now know that Miller and Urey's ideas on the composition of the early atmosphere were incorrect. • But new experiments based on current ideas of the early atmosphere have also produced organic compounds. • In fact, in 1995, one of Miller's more accurate mixtures produced cytosine and uracil • two nitrogenous bases found in the nucleotides of RNA

25. The leap from nonlife to life is the greatest gap in scientific hypotheses of life's early history. Even though their findings were remarkable, Miller and Urey did not simulate the origin of life.

26. Once simple, organic compounds were formed, polymers of carbs, proteins, lipids, and nucleic acids could give rise toprotocells Protocells simple precursors to cells then evolved into primitive cells with RNA as the genetic material.

28. Heterotroph Autotroph • heterotrophs Were the primitive cells autotrophs or heterotrophs? • Organism that obtains food by consuming other organisms. • Also called a consumer. • Requires external supply of energy in the form of food as it cannot synthesize its own • Organism that is able to capture energy from sunlight or chemicals and use it to produce its own food from inorganic compounds. • Also called a producer The Heterotroph Hypothesis:

29. Which form of life (autotrophic, heterotrophic) is a simpler design? • Heterotrophic • synthesis of high-energy organic molecules by autotrophs requries many enzymes & extra genes. • Heterotrophs are a simpler design (though their metabolism is still relatively complex)…but remember, autotrophs still have to do most of the same reactions as heterotrophs too!

30. Which form of cellular respiration (aerobic-uses O2, anaerobic-no O2 used) was used by these organisms? • Heterotrophs at this point must have been undergoing some type of anaerobic respiration (fermentation) • No O2 used

31. What’s an Anaerobic Heterotroph? Anaerobic heterotrophs consumed organic matter (organic “soup”) and underwent anaerobic respiration.

32. It is believed that the ancestors of all life on earth today, were anaerobic heterotrophic prokaryotes. Over time, organic nutrients were probably being used up faster than they were being formed. Evolutionary pressures next led to the development of...(drum roll, please)...autotrophs!

33. Summary of the effects of the evolution of photosynthesis on early Earth:

34. Oxygen began to accumulate in the atmosphere The ozone (O3) layer began to form, and the skies turned their present shade of blue. Oxygen concentrations continued to rise over the next several hundred million years, creating a crisis for certain organisms to which this oxygen gas was a deadly poison -- some early life forms were driven to extinction. Some organisms, however, evolved new metabolic pathways to protect themselves from oxygen's powerful reactive abilities by using that oxygen for respiration

38. Diversity of Life • Eukarya • Domain consisting of all organisms that have a NUCLEUS • Multicellular • Includes • Protists • Plants • Fungi • Animals • Prokaryotic • Consisting of organisms that LACK a nucleus • Unicellular • Includes Domains • Bacteria • “Eubacteria” • Archaea

39. Prokaryotic Eukaryotic Prokaryotic