PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25In one advance Louis PasteurLouis Pasteur discredited the concept of spontaneous generation. discredited the concept of spontaneous generation. He offered proof that even bacteria and other microorganisms arise from parents resembling themselves. microorganisms arise from parents resembling themselves. He thereby highlighted an intriguing question:How did the first generation of each species come into existence? When the earth formed some 4.6 billion years ago, it was a lifeless, inhospitable place. A billion years later it was teeming with organisms resembling blue-green algae. How did they get there? How, in short, did life begin?How, in short, did life begin? http://www.geocities.com/CapeCanaveral/Lab/2948/orgel.htmlLeslie E. Orgel… in the mid-19th century two important scientific advances set the stage for modern discussions of the origin of life.http://www.geocities.com/CapeCanaveral/Lab/2948/orgel.htmlThe theory therefore implied that all current life-forms could have evolved from a single, simple progenitorall current life-forms could have evolved from a single, simple progenitor - an organism now referred to as life's last common ancestorlife's last common ancestor. … individuals bearing traits that provide the best adaptation to the … environment meet with the greatest reproductive success. …… some of the differences between individuals in a population are heritable. In other words, environmental pressures select adaptive traits for perpetuation. Repeated generation after generation, natural selection natural selection could thus lead to the evolution of complex organisms from simple ones.could thus lead to the evolution of complex organisms from simple ones. The second advance, the theory of natural selectionthe theory of natural selection, suggested an answer. According to this proposal, set forth by Charles Darwin and Alfred Russell Wallace,For much of the 20th century, origin-of-life research has aimed to flesh out Darwin's private hypothesis - to elucidate how, without supernatural intervention, spontaneous interaction of the relatively simple molecules dissolved in the lakes or oceans of the prebiotic world could have yielded life's last common ancestorlife's last common ancestor. … it had to possess genetic informationit had to possess genetic information - heritable instructions … and the means to replicateand the means to replicate and carry out those instructions. Otherwise it would have left no descendants. Also, … its genetic material had to allow for some random variationits genetic material had to allow for some random variation in the heritable characteristics of the offspring so that new traits could be selected …Darwin …posited in the final paragraph of The Origin of Species that "the Creator" originally breathed life "into a few forms or into one." Then evolution took over: "From so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved." In private correspondence … he suggested life could have arisen through chemistry, life could have arisen through chemistry, "in some warm little pond, with all sorts of ammonia and"in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc. present." phosphoric salts, light, heat, electricity, etc. present." http://www.geocities.com/CapeCanaveral/Lab/2948/orgel.html… One can safely inferinfer that intricate features present in all modern varieties of life intricate features present in all modern varieties of life also appeared in thatalso appeared in that common ancestorcommon ancestor. …. …… all living things consist of similar organic (carbon-rich) compounds. … the proteins … are fashioned from one set of 20 standard amino acidsone set of 20 standard amino acids. …… carry their genetic information in nucleic acids - RNA and DNA - and use essentially the same genetic codeessentially the same genetic code. This code specifies the amino acid sequences of all the proteins …… … we can infer that our last common ancestor stored genetic information in we can infer that our last common ancestor stored genetic information in nucleic acids that specified the composition of all needed proteins.nucleic acids that specified the composition of all needed proteins.… … relied on proteins to direct … the reactions required for self-perpetuation.relied on proteins to direct … the reactions required for self-perpetuation. Hence, the central problem of origin-of-life research can be refined to ask, By what series of chemical reactions By what series of chemical reactions did this interdependent system of nucleic acids and proteins did this interdependent system of nucleic acids and proteins come into being? come into being? http://www.geocities.com/CapeCanaveral/Lab/2948/orgel.html… a paradoxa paradox. Nowadays nucleic acids are synthesized only with the help of proteins, and proteins are synthesized only if their … nucleotide sequence is present. Moreover, it was easy to envision ways that DNA could evolve from RNA and then, being more stable, take over RNA's role as the guardian of heredity. We suspected that RNA came before proteins … we had difficulty composing any scenario in which proteins could replicate in the absence of nucleic acids. C&R Fig 26.11 C&R Fig 26.13a world in which RNA catalyzed all the reactions necessary a world in which RNA catalyzed all the reactions necessary forfor a precursor ofa precursor of life's last common ancestorlife's last common ancestor to survive and replicateto survive and replicate. . … ribonucleotides in RNA are more readily synthesized than are the deoxyribonucleotides in DNA. In the late 1960s Carl R. Woese … Francis Crick … and I … independently … proposed that RNA might well have come first and established what is now called the RNA worldRNA world -http://www.geocities.com/CapeCanaveral/Lab/2948/orgel.html{similarities}{differences}… there is good reason to think the RNA world did exist and that RNA invented protein synthesis. Fortunately, even before the RNA-world hypothesis was proposed, investigators had gained useful