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L03 - Origins of Life

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Biology 1001A
Tom Haffie

Lecture 3 – Origins (September 17, 2012) What do we know about Life? - Earth is 4.6 billion years old - We have geological evidence of life from 4.5 bya * ex. Stromatolites (good example of something produced by microbial activity) - Perhaps the start of life 4 billion years ago - All domains of life are derived from a single point (Bacteria, Archaea, Eukaryotes) * Last Universal Common Ancestor (LUCA) - What do all these things have in common? Biochemical things all living things have 1. Cells are made of lipids 2. Genetic system based on DNA 3. DNA to RNA to Protein transfer of information (central dogma) 4. Common system of protein assembly 5. ATP 6. Glucose & Glycolysis What came before LUCA? - Many initial forms of life were produced - Some had RNA as genetic system, perhaps didn’t have lipid membranes - ONLY ONE LASTED Prokaryotic Cells do NOT Exist - Archaea are NOT related to bacteria at all - Archaea and Bacteria should not be grouped as prokaryotes b/c they are NOT the same thing and cannot be classified together. - There is no single group of organisms - “Pro” means anteriority - Suggests directionality in evolution (from simple  complex) which is NOT true - Evolution does not always run in this direction (another misconception) - Bacteria may have been evolved through reductive evolution - Reductive evolution – streamlining out the things that it does not need to function/ things that would make it more energy efficient (increased energy efficiency  faster reproduction, extremophiles) Extremophiles – growing in an extreme environment b/c they are so simplified that they can adapt rapidly Perhaps LUCA was a proto-eukaryotic cell Stages of Prebiotic Evolution - What do you need to make life? Abiotic Synthesis Heritable information Cells Metabolism Stages of Production of Life - Geophysical stage (composition of the atmosphere) - Chemical stage ( building blocks – how are they synthesized) - Biological Stage (How did the building blocks organize into living cells?)  POORLY UNDERSTOOD Ex. Australopithecus afarensis (Hominid evolution) Time is phenomenally distant Chemical Stage - Miller Urey experiment leaves unanswered questions: * Development of polymers * Chirality : - Two enantiomers (optical isomers, mirror images but not the same) - chiral molecules can have VASTLY different biological properties ex. Thalidomide (antiemetic drug in 50s) comes in two Chiral forms, one leads to birth defects and another leads to poor limb development - Life is Homochiral * we use one form of amino acids (L amino acids) and one form of sugars (D sugars) * essential to the evolution of life * Miller-Urey produced RACEMIC (mixture of the right and wrong types of amino acids & sugars) * Complexity of having to accept several sugars/aa’s was selected against and organisms are specific Biological Stage - Heritable information, cells, metabolism - GREAT hypothesis on heritable information (Central dogma)
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