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Origin of Life Today How did life originate? Working back from today The most basic components How DNA and RNA work Working forward from simple molecules Bridging the gap Debate: how easily does life arise? Current Life: Animals and Plants • Very complex • Many organs, tissues with specialized functions QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. The Origins of Life on Earth • What is the simplest form of life today? The cell Eukaryotes Prokaryotic Cell The Origins of Life on Earth What about viruses? • Smallest form of “life” – if considered life • Genetic material is DNA or RNA Prions The Origins of Life on Earth • And herein lies the rub…. Viruses and Prions are dependent on hijacking the DNA of the host cell to reproduce.. • Which is the chicken and which is the egg… Sizes of Organisms • • • • Smallest eukaryote: 10^ 11atoms Smallest prokaryote: 10^ 9 atoms Smallest virus: 10^6 atoms Smallest prion/viroid: 10^3 atoms • Even smallest of these had to have smaller ancestors! Giant Molecular Clouds • Amino acids and other • Organic Molecules The Origins of Life on Earth • Miller-Urey Experiment – showed that complex molecules can be made with simple chemical reactions The Origins of Life on Earth The Origins of Life on Earth • Miller-Urey Experiment: did not produce any self-replicating molecules Today-debate about the composition of Earth’s early atmosphere Water • Polar Molecule Phospholipids Cell Membrane What about self-replicating molecules? Eukaryotic Cell • DNA contains genetic code • Gives instructions to mRNA • Instructions then transcribed by ribosome The Origins of Life on Earth The Origins of Life on Earth • Proteins serve a wide variety of functions– Best known is as enzymes Enzymes are needed to unzip the DNA for mRNA to read Chicken and egg? Gap in Understanding • DNA- is too complicated to have been first genetic molecule • Noted that some organisms use RNA instead. DNA vs RNA RNA in eukaryote cell • mRNA – messenger RNA is copied from part of the DNA and contains the blueprint for a protein • tRNA – delivers amino acids to ribosomes for building proteins • rRNA – ribsome RNA which does the decoding of mRNA • Ribosomes – structures of RNA and proteins which build proteins from amino acids delivered by transfer RNA QuickTime™ and a decompressor are needed to see this picture. DNA vs. RNA • RNA can duplicate itself • Catalyze reactions that produce subunits of RNA (more building blocks!) • Catalyze chains of amino acids which can be used to produce proteins! The Origins of Life on Earth RNA World Hypothesis: The first genetic molecule used was RNA not DNA. The Origins of Life on Earth RNA World Hypothesis: • Hypothesis that RNA were the first selfreproducing molecules. • They were capable of making themselves and proteins • Later evolved to make DNA, and later evolved into DNA dominated world. RNA world in eukaryote cell • mRNA – messenger RNA is copied from part of the DNA and contains the blueprint for a protein • tRNA – delivers amino acids to ribosomes for building proteins • rRNA – ribsome RNA which does the decoding of mRNA • Ribosomes – structures of RNA and proteins which build proteins from amino acids delivered by transfer RNA QuickTime™ and a decompressor are needed to see this picture. The Origins of Life on Earth What is the bare minimum for “life”? Perhaps the first “life” included the concept of a cell…. The RNA reproduced when the soup was concentrated enough… for whatever reason…. The step to RNA is huge. We don’t know how it happened! Gerald Joyce Lab • Scripps, in CA • Fitness of RNA, putting in only basic chemicals • Lenski-like: let run, take out solution, put in fresh batch • See clear improvement of fitness The Origins of Life on Earth • Working in the forward direction…. • From simple molecules to life? • We know a lot about the conditions on the Earth 4 Billion years ago. liquid water carbon dioxide methane ammonia hydrogen light geothermal energy The Origins of Life on Earth • Continuing extensions of the experiments with best estimates of the early Earth’s atmosphere continue at a modest level. • Experiments can produce amino acids, sugars. • No experiment to date has produced self-replicating molecules. • All of the chemistry is driven by the energy input in the form of “lightning” or light. • Biological and non-biological molecules are produced in these experiments The Origins of Life on Earth What is the bare minimum for “life”? • RNA – some molecule complex enough to carry genetic blueprints for the organism. • Cell wall – something to protect the RNA from the raw environment and contain replication • A rich organic soup of less complex molecules to “eat” Nature of Cell Walls Water is a polar molecule Negative on one side Positive on the other • Other polar molecules “like” water; nonpolar don’t • Phospholipids: one water-liking side, one water hating