Origin & Evolution of Life PDF

Origin & Evolution of Life Module 2 Dr. Priyanka Singh Department of Bioscience & Bioengineering IIT Jodhpur To account for the origin of life on our earth requires solving several problems: How the organic molecules that def...

Origin & Evolution of Life Module 2 Dr. Priyanka Singh Department of Bioscience & Bioengineering IIT Jodhpur To account for the origin of life on our earth requires solving several problems: How the organic molecules that define life, e.g. amino acids, nucleotides, were created. How these were assembled into macromolecules, e.g. proteins and nucleic acids, - a process requiring catalysts. How these were able to reproduce themselves. How these were assembled into a system delimited from its surroundings (i.e., a cell). How the organic molecules that define life, were created? Proposed scenarios: Organic molecules: 1. were synthesized from inorganic compounds in the atmosphere, 2. Molecules from Outer Space 3. were synthesized at hydrothermal vents on the ocean floor, Scenario 1: Miller's Experiment At the end of a week, Miller used paper chromatography to show that the flask now contained several amino acids as well as some other organic molecules. However, it is now thought that the atmosphere of the early earth was not rich in methane and ammonia - essential ingredients in Miller's experiments. In the years since Miller's work, many variants of his procedure have been tried. Virtually all the small molecules that are associated with life have been formed Miller experiment  Scenario 2 Scenario 3 Astronomers, using infrared spectroscopy, have identified Some deep-sea hydrothermal vents discharge a variety of organic molecules in interstellar space copious amounts of hydrogen, hydrogen sulfide, and carbon dioxide at temperatures around 100°C These gases bubble up through chambers rich in iron sulfides (FeS, FeS2). These can catalyze the formation of simple organic molecules like acetate. (And life today depends on enzymes that have Fe and S atoms in their active sites.) Murchison meteorite at the The National Museum of Natural History (Washington). Assembling Polymers In solution, hydrolysis of a growing polymer would soon limit the size it could reach. Abiotic synthesis produces a mixture of L and D enantiomers. Each inhibits the polymerization of the other. (So, for example, the presence of D amino acids inhibits the polymerization of L amino acids (the ones that make up proteins here on earth). Theory: early polymers were assembled on solid, mineral surfaces that protected them from degradation, “RNA world” Reproduction? Perhaps the earliest form of reproduction was a simple fission of the growing aggregate into two parts - each with identical metabolic and genetic systems intact. The First Cell? To function, the machinery of life must be separated from its surroundings : Plasma Membrane (lipid bilayer) fatty acids, fatty alcohols, and monoglycerides - all molecules that can be synthesized under prebiotic conditions - can also form lipid bilayers and these can spontaneously assemble into enclosed vesicles. From Unicellular to Multicellular Organisms colonial flagellated green algae provide a clue. The Last Universal Common Ancestor (LUCA)? Researchers believe that all life forms— the Bacteria, the Archaea, and the Eukarya —originated from a single cell known as the last universal common ancestor (LUCA). It is suggested to have been a “cellular organism that had a lipid bilayer and used DNA, RNA, and protein“. There is a lack of clarity about direct fossil evidence of LUCA. However, the shared features of modern genomes provide significant insights into this ancient ancestor. Inquiring About Life An organism’s adaptations to its environment are the result of evolution For example, the color of the beach mouse has come to be well matched, or adapted, to its local background Evolution is the process of change that has transformed life on Earth Properties of life Growth and development Reproduction Energy flow Adaptations Regulation Order Response to the environment Living systems can last for a long time because they are self-organizing and can adapt to change. Living systems are open systems that interact with their environment and are maintained by flows of energy, matter, and information Theme: Emergent Properties “Novel properties absent at one level that emerge at a new level” Result from the arrangement and interaction of parts within a system Emergent properties characterize non-biological entities as well For example, a functioning bicycle emerges only when all of the necessary parts connect in the correct way Structure and Function At each level of the biological hierarchy, we find a correlation between structure and function Analyzing a biological structure gives us clues about what it does and how it works Conversely, knowing the function of something provides insight into its structure and organization  The Biological Purpose of Cellular and Organism Structures 1. Supporting structures, not directly involved in processes which constitute life, but providing a framework and foundation for such processes. 2. Structures directly involved in the functioning of living organisms, i.e., those that facilitate metabolism and motion. 3. Storage structures, i.e., structures used to store information and energy. The factory as an autonomous entity with subunits which fulfill (a) supporting, (b) functional, and (c) storage tasks