Prebiotic evolution

THEORIES ON HOW LIFE CAME ABOUT

1. PREBIOTIC EVOLUTION By: Alizay BS MICROBIOLOGY AND MOLECULAR GENETICS THE WOMEN UNIVERSITY MULTAN

2. Evolution , as the term is used here, signifies any development or change adapting to the environment.   Prebiotic Evolution  refers to evolution before life, describing ideas about how life began from a ‘prebiotic soup’.

3. CONDITIONS ON EARTH BEFORE Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide , carbon monoxide , nitrogen , hydrogen sulfide , and water. Volcanic activity probably formed it. Released great amounts of water vapor that later condensed to form oceans. Released CO2 that warms the atmosphere by absorbing outgoing heat.

4. A common theme is that the ingredients for life were generated by the flow of energy ( sunlight, lightning, or thermal radiation ) through the primordial hydrosphere so that the putative mechanisms for the origin of life should be compatible with the conditions that would have prevailed in the early atmosphere and oceans.

5. How life came about? FOSSIL EVIDENCE HYDROTHERMAL VENTS However, evidence of extant organisms appears in fossilized stromatolites in Western Australia from 3.5 billion years ago, suggesting that the appearance of life occurred quite rapidly on a geologic time scale once the conditions were favourable These vents release important hydrogen-rich Molecules Mineral catalysts could have critical reactions occurs faster

6. CLAY PANSPERMIA Clay may have provided the foundation for first organic compounds. Mineral crystals in clay could have arranged organic compounds into organized patterns. Life could have come from outer space in a comet or meteorite.

7. ELECTRIC SPARK A historic demonstration of the feasibility of prebiotic simulations was performed by Stanley Miller during the fall of 1952 in the laboratory of Harold Urey at the University of Chicago They theorized that electric spark can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen

8. OPARIN-HALDENE THEORY ( Primordial Soup Theory ) Oparin reasoned that O2 prevents the synthesis of certain organic compounds that are necessary building blocks for the evolution of Life Oparin proposed that the "spontaneous generation of life" did in fact occur once, but was now impossible because the conditions found on the early Earth had changed Oparin argued that a "primeval soup" of organic molecule could be created in an oxygen-less atmosphere.

9. BIOGENESIS Biogenesis states that every living thing came from a pre-existing living thing. In 1668 Francesco Redi , proved that no maggots appeared in meat when flies were prevented from laying eggs. In 1768, Lazzaro Spallanzani demonstrated that microbes were present in the air, and could be killed by boiling. In 1861, Louis Pasteur performed a series of experiments which demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media.

10. Appearance of oxygen About 2.7 b.y.a ., cyanobacteria or blue-green algae began photosynthetic reactions About 1.8 b.y.a , the atmosphere contained abundant free oxygen. Allowed for the development of more complex, oxygen-breathing life forms Caused the first mass extinction of organism that had evolved in an oxygen-less planet Ended the process of chemical evolution

11. Spirulina

12. Physical Structures That May Have Given Rise To The First Cells Cell like structures, including microspheres and coacervates , form spontaneously in certain kinds of solutions. Polysaccharides form coacervates in solution. Membrane-like boundary Act like cells Absorb molecules and release products Form new spheres by budding

13. ENDOSYMBIOTIC THEORY According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotic organisms.

14. RNA-World Hypothesis RNA is a complex molecule found in all living things that seems to be able to catalyze its own reproduction. According to this "RNA World" hypothesis, RNA was the crux molecule for primitive life and only took a backseat when DNA and proteins—which perform their jobs much more efficiently than RNA—developed.

15. But the RNA World hypothesis doesn't explain how RNA itself first arose. Like DNA, RNA is a complex molecule made of repeating units of thousands of smaller molecules called nucleotides that link together in very specific, patterned ways. While there are scientists who think RNA could have arisen spontaneously on early Earth, others say the odds of such a thing happening are astronomical.

16. Cyanide John Oro at the University of Houston in 1960 made a startling observation: adenine , a constituent of RNA as well as the nicotinamide and flavin cofactors, was formed after acid hydrolysis of ammonium cyanide solutions, which were deemed prebiotic starting materials based on the prior detection of HCN in the Miller-Urey electric discharge reactions

17. HCN oligomerization also provides a source of the RNA component , uracil , which was first identified in such a mixture by Alan Schwartz and Andries Voet at the University of Nijmegen

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