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Pahs (Polycyclic Aromatic Hydrocarbons) and the Origins of Life

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Pahs (Polycyclic Aromatic Hydrocarbons) and the Origins of Life PAHsPAHs (Polycyclic(Polycyclic AromaticAromatic Hydrocarbons)Hydrocarbons) andand thethe OriginsOrigins ofof LifeLife Alexander Karol Padden Murphy Scott Pruessing WhatWhat AreAre PAHsPAHs?? z PAHSPAHS areare veryvery stablestable organicorganic moleculesmolecules mademade upup ofof onlyonly carboncarbon andand hydrogenhydrogen z PAHSPAHS areare planerplaner andand areare mademade upup ofof ringsrings thatthat areare fusedfused togethertogether z PAHSPAHS isis anan acronymacronym forfor "polycyclic"polycyclic aromaticaromatic hydrocarbons"hydrocarbons" z The “polycyclic” refers to fact that they are multiple rings of carbon atoms z The "aromatic" refers to the kinds of strong chemical bonds that exist between the carbon atoms. z The "hydrocarbon" refers to atomic composition, which is hydrogen and carbon. WhatWhat AreAre PAHsPAHs?? (Cont.)(Cont.) z PAHsPAHs havehave manymany differentdifferent typestypes andand isomersisomers ofof hydrogenhydrogen andand carboncarbon z PAHs commonly range from three to seven member rings, but most often have five or six z PAHs with more than six rings are “large” while those with more than six are called “small” z PAHs decrease in solubility as the ring number increases, so as a result they are more commonly found in oils and sediments. WhereWhere areare PAHsPAHs foundfound onon Earth?Earth? z On Earth, PAHs are formed by the partial combustion of carbon products z PAHS are lipophilic, and are therefore commonly found in oils and fats. z Examples where PAHs are found: z Coal z Diesel z Fats z Wood z Edible Oils z Tobacco z Most PAHs have no use, and are often known carcinogens. z Some PAHs are used to make: z Medicines z Plastics z Pesticides z Mothballs z Dyes z Anabolic Steroids PAHsPAHs outsideoutside ofof EarthEarth z TheThe NASANASA SpitzerSpitzer SpaceSpace TelescopeTelescope detectsdetects PAHsPAHs inin twotwo waysways z IRAC (Infrared Array Camera) z IRS (Infrared Spectrograph) z PAHsPAHs havehave beenbeen foundfound toto existexist inin thethe redred spectralspectral raysrays ofof aa dyingdying nebulanebula z TwoTwo typestypes ofof PAHsPAHs,, AnthraceneAnthracene andand PyrenePyrene,, werewere foundfound toto occuroccur inin thethe RedRed RectangleRectangle nebulanebula 10001000 lightlight yearsyears fromfrom Earth.Earth. TheoryTheory TimeTime z EverythingEverything fromfrom herehere onon outout basedbased inin fact,fact, butbut isis theorytheory z EmergingEmerging FieldField asas wewe havehave justjust beenbeen decodingdecoding thethe HumanHuman genomegenome z TheoriesTheories veryvery recentrecent RNARNA WorldWorld z HypothesisHypothesis thatthat RNARNA waswas thethe formationformation ofof lifelife z ContainsContains geneticgenetic informationinformation z ActsActs asas aa ribozymeribozyme,, similarsimilar toto anan enzymeenzyme FormationFormation TheoryTheory z NucleicNucleic acidsacids floatingfloating aroundaround inin thethe primordialprimordial soupsoup z MostMost formedformed bondsbonds weakweak andand breakbreak upup z SomeSome basebase pairspairs havehave catalyticcatalytic sequencingsequencing causingcausing themthem toto holdhold togethertogether togethertogether andand growgrow longerlonger FormationFormation TheoryTheory z RNA can self replicate z Formed a natural selection process z More efficient RNA lived and procreated z Developed proteins, dna, lipids, carbohydrates, and other molecules ProblemsProblems z ThereThere areare manymany problemsproblems withwith thethe formationformation theorytheory z RNARNA isis fragilefragile andand wouldwould likelylikely notnot formform onon itsits ownown z NucleotidesNucleotides mustmust bebe activatedactivated toto formform RNA,RNA, doesndoesn’’tt happenhappen autonomouslyautonomously z NucleotidesNucleotides dodo notnot stackstack wellwell onon theirtheir ownown PAHPAH WorldWorld z TheoryTheory forfor thethe formationformation ofof RNARNA z PAHsPAHs areare aa likelylikely constituentconstituent ofof thethe primordialprimordial soupsoup z PAHsPAHs areare amphiphilicamphiphilic andand tendtend toto stackstack withwith eacheach otherother withwith aa separationseparation ofof .034nm..034nm. z RNARNA andand DNADNA basesbases havehave aa separationseparation ofof .034nm..034nm. z Coincidence?Coincidence? PAHPAH WorldWorld (Cont.)(Cont.) z PAHsPAHs stackstack hydrophilichydrophilic endend out.out. z MoleculesMolecules attachattach toto them,them, butbut PAHsPAHs swivelswivel aroundaround eacheach otherother andand dislodgedislodge thesethese molecules.molecules. z PyrimidinesPyrimidines andand PurinesPurines cancan staystay attachedattached becausebecause theythey areare flatflat andand dodo notnot dislodgedislodge eacheach other.other. PAHPAH WorldWorld (Cont.)(Cont.) z Pyrimidines and Purines (Nucleic Bases) also are amphiphilic and line up in stacks. z Makes a scaffold for nucleic acid backbones to form. z Change in acidity would allow the chain to break off and form RNA. ConclusionConclusion z PAHsPAHs areare knownknown toto bebe foundfound bothboth inin thethe interstellarinterstellar mediummedium andand herehere onon Earth.Earth. z PAHsPAHs maymay havehave beenbeen thethe moleculesmolecules thatthat firstfirst formedformed RNA.RNA. z TheThe ideaidea ofof aa PAHPAH basedbased initiationinitiation toto thethe RNARNA worldworld isis veryvery appealingappealing butbut asas ofof yetyet untested.untested. ReferencesReferences z http://www.newscientist.com/article.ns?id=dn4552 z //www.npi.gov.au/database/substance- info/profiles/74.html z http://www.iupac.org/general/search.php z http://www.spitzer.caltech.edu/features/articles/2005062 7.shtml z http://en.wikipedia.org/wiki/Pahs z http://en.wikipedia.org/wiki/PAH_world_hypothesis z http://www.newscientist.com/article.ns?id=dn4552 z http://www.talkorigins.org/faqs/abioprob/originoflife.html z http://www.pahworld.com/ z http://en.wikipedia.org/wiki/RNA_World.
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