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5.5: Eerste organiese molekules - Biologie

5.5: Eerste organiese molekules - Biologie


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Hoe maak jy groot molekules?

Van kleineres. Die eerste organiese molekules was waarskynlik baie eenvoudige koolstofgebaseerde molekules wat uit min atome bestaan. Hierdie molekules word dan gekombineer met ander eenvoudige molekules om meer komplekse molekules te vorm. Oor baie jare en waarskynlik triljoene en triljoene van chemiese reaksies, het meer komplekse molekules en meer stabiele molekules gevorm.

Die eerste organiese molekules

Alle lewende dinge bestaan ​​uit organiese molekules, gesentreer rondom die element koolstof. Daarom is dit waarskynlik dat organiese molekules voor selle ontwikkel het, miskien so lank as 4 miljard jaar gelede. Hoe het hierdie boustene van die lewe eers ontstaan?

Wetenskaplikes dink dat weerlig chemiese reaksies in die aarde se vroeë atmosfeer veroorsaak het. Die vroeë atmosfeer het gasse soos ammoniak, metaan, waterdamp en koolstofdioksied bevat. Wetenskaplikes veronderstel dat dit 'n "sop" van organiese molekules uit anorganiese chemikalieë geskep het.

In 1953 het wetenskaplikes Stanley Miller en Harold Urey hul verbeelding gebruik om hierdie hipotese te toets. Hulle het 'n simulasie -eksperiment gemaak om te sien of organiese molekules op hierdie manier kan ontstaan ​​(sien Figuur hieronder). Hulle het 'n mengsel van gasse gebruik om die aarde se vroeë atmosfeer voor te stel. Daarna het hulle vonke deur die gasse gelei om weerlig te verteenwoordig. Binne 'n week het verskeie eenvoudige organiese molekules gevorm.

U kan 'n dramatisering van Miller en Urey se eksperiment op hierdie skakel sien: https: //www.youtube.com/watch? V = NNijmxsKGbc.

Watter organiese molekule het eerste gekom?

Lewende dinge het organiese molekules nodig om genetiese inligting op te slaan en om die chemiese werking van selle uit te voer. Moderne organismes gebruik DNA om genetiese inligting en proteïene te stoor om chemiese reaksies te kataliseer. Het DNA of proteïene eers ontwikkel? Dit is soos om te vra of die hoender of die eier eerste kom. DNS kodeer proteïene en proteïene is nodig om DNS te maak, so elke tipe organiese molekule het die ander nodig vir sy eie bestaan. Hoe kon een van hierdie twee molekules voor die ander ontwikkel het? Het 'n ander organiese molekule eers ontwikkel, in plaas van DNA of proteïene?

RNA Wêreldhipotese

Sommige wetenskaplikes spekuleer dat RNA moontlik die eerste organiese molekule was wat ontwikkel het. Hulle dink eintlik dat die vroeë lewe slegs op RNA gebaseer was en dat DNA en proteïene later ontwikkel het. Dit word die RNA wêreld hipotese. Waarom RNA? Dit kan genetiese instruksies (soos DNA) kodeer, en sommige RNA's kan chemiese reaksies (soos proteïene) uitvoer. Daarom los dit die hoender-en-eier-probleem op, waarvan een van hierdie twee molekules eerste gekom het. Ander bewyse dui ook daarop dat RNA die oudste van die organiese molekules is. U kan meer leer oor die RNA -wêreldhipotese en die bewyse daarvoor op hierdie skakel: http: //www.youtube.com/watch? V = sAkgb3yNgqg.

Opsomming

  • Die eerste organiese molekules het sowat 4 miljard jaar gelede gevorm.
  • Dit het moontlik gebeur toe weerlig chemiese reaksies in die vroeë atmosfeer van die aarde veroorsaak het.
  • RNA was moontlik die eerste organiese molekule wat gevorm het, sowel as die basis van die vroeë lewe.

Verken meer

Gebruik die tydskuif in hierdie bron om die daaropvolgende vrae te beantwoord.

  • Evolusie by http://johnkyrk.com/evolution.swf.
  1. Wanneer het die element koolstof die eerste keer gevorm?
  2. Wanneer het die eerste elemente in die aarde se atmosfeer en op die oppervlak daarvan verskyn?
  3. Lys 5 van hierdie vroeë chemikalieë.
  4. Wanneer het die eerste organiese molekules verskyn?
  5. Wat was hierdie eerste organiese molekules? Hoe het hierdie organiese molekules opgehoop?

Resensie

  1. Beskryf Miller en Urey se eksperiment. Wat het dit getoon?
  2. Noem die RNA-wêreldhipotese.

Verskil tussen organiese en anorganiese molekules

Al die molekules kan grootliks in twee groepe verdeel word as organies en anorganies. Daar is verskillende studiegebiede rondom hierdie twee tipes molekules ontwikkel. Hul strukture, gedrag en eienskappe verskil van mekaar.

Organiese molekules

Organiese molekules is molekules wat bestaan ​​uit koolstofstowwe. Organiese molekules is die volopste molekule in lewende dinge op hierdie planeet. Die belangrikste organiese molekules in lewende dinge is koolhidrate, proteïene, lipiede en nukleïensure. Nukleïensure soos DNA bevat genetiese inligting van organismes. Koolstofverbindings soos proteïene maak strukturele komponente van ons liggame, en hulle vorm ensieme wat al die metaboliese funksies kataliseer. Organiese molekules bied ons energie om daaglikse funksies uit te voer. Daar is bewyse dat koolstofmolekules soos metaan selfs 'n paar biljoen jaar gelede in die atmosfeer bestaan ​​het. Hierdie verbindings met die reaksie met ander anorganiese verbindings was verantwoordelik vir die opwekking van lewe op aarde. Ons bestaan ​​nie net uit organiese molekules nie, maar daar is ook baie soorte organiese molekules wat ons elke dag vir verskillende doeleindes gebruik. Die klere wat ons dra is saamgestel uit óf natuurlike óf sintetiese organiese molekules. Baie van die materiale in ons huise is ook organies. Petrol, wat energie aan motors en ander masjiene gee, is organies. Die meeste medisyne, plaagdoders en insekdoders, bestaan ​​uit organiese molekules. Organiese molekules word dus met byna elke aspek van ons lewens geassosieer. Daarom het 'n aparte onderwerp as organiese chemie ontwikkel om meer te leer oor hierdie verbindings. In die agtiende en negentiende eeu is belangrike vordering gemaak in die ontwikkeling van kwalitatiewe en kwantitatiewe metodes vir die ontleding van organiese verbindings. In hierdie tydperk is empiriese formule en molekulêre formules ontwikkel om molekules afsonderlik te identifiseer. Koolstofatoom is tetravalent, sodat dit slegs vier bindings rondom dit kan vorm. En 'n koolstofatoom kan ook een of meer van sy valensies gebruik om bindings aan ander koolstofatome te vorm. Koolstofatoom kan óf enkel-, dubbel- of drievoudige bindings met 'n ander koolstofatoom of enige ander atoom vorm. Koolstofmolekules het ook die vermoë om as isomere te bestaan. Hierdie vermoëns stel koolstofatoom in staat om miljoene molekules met verskillende formules te maak. Koolstofmolekules word algemeen geklassifiseer as alifatiese en aromatiese verbindings. Hulle kan ook as takke of onvertak gekategoriseer word. 'N Ander kategorisering is gebaseer op die tipe funksionele groepe wat hulle het. In hierdie kategorisering word organiese molekules verdeel in alkane, alkene, alkyne, alkohole, eter, amien, aldehied, keton, karboksielsuur, ester, amied en haloalkane.

Anorganiese molekules

Diegene wat nie aan organiese molekules behoort nie, staan ​​bekend as anorganiese molekules. Daar is 'n groot verskeidenheid, in terme van geassosieerde elemente, in anorganiese molekules. Minerale, water, die meeste van die oorvloedige gasse in die atmosfeer is anorganiese molekules. Daar is anorganiese verbindings wat ook koolstof bevat. Koolstofdioksied, koolstofmonoksied, karbonate, sianiede, karbiede is 'n paar voorbeelde van hierdie tipe molekules.

Wat is die verskil tussen organiese en anorganiese molekules?

• Organiese molekules is gebaseer op koolstofstowwe, en anorganiese molekules is gebaseer op ander elemente.

• Daar is sommige molekules wat as anorganiese molekules beskou word alhoewel hulle koolstofatome bevat. (bv. koolstofdioksied, koolstofmonoksied, karbonate, sianiede en karbiede). Daarom kan organiese molekules spesifiek gedefinieer word as molekules wat CH-bindings bevat.

• Organiese molekules kom meestal voor in lewende organismes waar anorganiese molekules meestal in nie -lewende stelsels voorkom.

• Organiese molekules het hoofsaaklik kovalente bindings, terwyl daar in anorganiese molekules kovalente en ioniese bindings is.

• Anorganiese molekules kan nie langketting polimere vorm soos organiese molekules dit doen nie.


Stikstofsiklus (Met Diagram) | Plantfisiologie

Stikstof is die vierde mees algemene element in lewende stelsels. Dit is 'n bestanddeel van 'n aantal organiese verbindings soos aminosure, proteïene, nukleotiede, nukleïensuur, hormone, chlorofil, baie vitamiene, ens.

Die beskikbaarheid en skaamte daarvan uit die grond is egter beperk, en selfs daarvoor moet plante meeding met mikrobes in natuurlike en landbou -ekosisteme. Stikstof is in die atmosfeer in oorvloed beskikbaar (78% van die atmosfeer as di-stikstof of N2) maar plante kan dit nie direk absorbeer nie.

Daarom is stikstof die belangrikste element. 'n Gereelde toevoer van stikstof aan die plante word deur stikstofsiklus gehandhaaf. Stikstofsiklus is gereelde sirkulasie van stikstof tussen lewende organismes, reservoirpoel in die atmosfeer en fietsrypoel in die litosfeer. Stikstofverbindings word verkry uit reservoirpoel deur stikstofbinding.

Die reservoirpoel word aangevul deur ontnitrifisering van nitrate en vrystelling van stikstof uit verrottende organiese materiaal. Fietsbad word aangevul deur ammonifikasie en nitrifikasie. Plante verkry stikstof uit die grond as NO3 – (nitraat), NH4 + (ammonium) en NO2– (nitriet) ione. Nitraat en nitriet word verminder tot ammonium, wat dan in aminosure, proteïene en ander organiese stowwe opgeneem word.

Dit is die omskakeling van inerte atmosferiese stikstof of di-stikstof (N2) in bruikbare stikstofverbindings soos nitraat, ammoniak, aminosure, ens. Daar is twee metodes van stikstofbinding - abiologies en biologies. Abiologiese stikstofbinding is verder van twee soorte, natuurlik en industrieel.

Natuurlike abiologiese stikstofbinding:

Atmosferiese stikstof kombineer met suurstof in die teenwoordigheid van elektriese ontladings, osonisering en verbranding. Verskillende tipes stikstofoksiede word vervaardig. Die stikstofoksiede los in water op en gee aanleiding tot hiponitriese, stikstofgas en salpetersure. Hulle kom in die grond saam met reënwater wat hiponitriete, nitriete en nitrate vorm.

Industriële abiologiese stikstofbinding:

Ammoniak word industrieel vervaardig deur direkte kombinasie van stikstof met waterstof (wat uit water verkry word) by hoë temperatuur en druk. Dit word verander na verskillende soorte kunsmis, insluitend ureum.

Biologiese stikstofbinding:

Dit is die tweede belangrikste natuurlike proses en die belangrikste bron van stikstofbinding wat deur twee soorte prokariote, bakterieë en sianobakterieë (= blougroen alge) uitgevoer word.

Hulle sluit beide vrylewende en simbiotiese vorms in:

(a) vry lewende stikstofbindende bakterieë:

Azotobacter, Beijerinckia (albei aërobies) en Bacillus, Klebsiella, Clostridium (almal anaërobies) is saprotrofiese bakterieë wat stikstofbinding uitvoer. Desulphovibrio is 'n chemotrofiese stikstofbindende bakterie. Rhodopseudomonas, Rhodospirillum en Chromatium is stikstofbindende anaërobiese foto -outotrofiese bakterieë. Vry lewende stikstofbindende bakterieë voeg 10-25 kg stikstof/ha/jaar by.

(b) Sianobakterieë wat vrye lewende stikstof herstel:

Baie vrylewende blougroen alge (BGA) of sianobakterieë voer stikstofbinding uit, bv. Anabaena, Nostoc, Calothrix, Lyngbia, Aulosira, Cylindrospermum, Trichodesmium. Hulle voeg 20-30 kg stikstof per hektaar grond en waterliggame by.

Sianobakterieë is ook ekologies belangrik, aangesien dit voorkom in water- en skuilgrond waar denitrifiserende bakterieë aktief kan wees. Aulosira fertilissima is die mees aktiewe stikstofbinder in ryslande terwyl Cylindrospermum aktief is in suikerriet- en mielielande.

(c) Simbiotiese stikstofbindende sianobakterieë:

Anabaena- en Nostoc -spesies is algemene simbiote in ligene, Anthoceros, Azolla en Cycad -wortels. Azolla pinnata ('n watervaring) het Anabaena azollae in sy blare. Dit word dikwels in ryslande ingeënt vir stikstofbinding.

(d) Simbiotiese stikstofbindende bakterieë:

Rhizobium is stikstofbindende bakteriese sim­biont van papilionagtige wortels. Sesbania rostrata het Rhizobium in wortelknoppies en Aerorhizobium in stamknoppies.

Frankia is simbiont in wortelknoppies van verskeie nie-peulplante soos Casuarina (Australiese denne), Myrica en Alnus (Alder). Xanthomonas en Mycobacterium vorm simbiotiese assosiasie met die blare van verskeie lede van rubiaceae en myrsinaceae (bv. Ardisia).

Beide Rhizobium en Frankia leef vry as aërobies in die grond, maar kan nie stikstof herstel nie. Hulle ontwikkel die vermoë om stikstof slegs as 'n simbiont vas te maak wanneer dit anaërobies word. Rhizobium is 'n staafvormige bakterie, terwyl Frankia 'n actinomycete is.

Hieruit is Rhizo­bium die belangrikste vir gewaslande omdat dit geassosieer word met peulgewasse en ander peulgewasse van familie fabaceae, bv. Kekerertjie of Gram (Cicer arietinum), Duifertjie of Rooi Gram (Cajanus cajan), Tuin- of Eetbare Ertjie ( Pisum sativum), Sojaboon (Glycine max), Lentil (Lens culinaris), Groen Gram (Vigna radiata = Phaseolus aureus), Swart Gram (Vigna of Phaseolus mungo), Soetklawer, Soetertjie, Lusern, Breëboontjie, Klawerboon. Verskeie spesies van die bakterie (bv. Rhizobium leguminosarum, R. meliloti) leef in die grond.

Hulle kan nie self stikstof regmaak nie. Die wortels van 'n peulgewas skei chemiese aantrekmiddels af (flavonoïede en betaines). Bakterieë versamel oor die wortelhare, stel knikfaktore vry wat wortelhare om die bakterieë laat krul, agteruitgang van selwand en vorming van 'n infeksiedraad wat die bakterieë omhul (Fig. 12.11).

Infeksiedraad groei saam met vermeerdering van bakterieë. Dit vertak en sy ente kom oorkant protokileempunte van die vaskulêre string lê. Die besmette kortikale selle dedifferensieer en begin verdeel. Dit produseer swellings of knoppies.

Knoopvorming word gestimuleer deur auxien wat deur kortikale selle geproduseer word en sitokinien wat deur indringende bakterieë vrygestel word. Die besmette selle vergroot. Bakterieë hou op om te verdeel en vorm onreëlmatige veelvlakkige strukture wat bakteriodes genoem word (Fig. 12.12). Sommige bakterieë behou egter normale struktuur, verdeel en dring nuwe gebiede binne. In 'n besmette sel kom bakterieë voor in groepe omring deur gasheermembraan.

Die gasheersel ontwikkel 'n pienkerige pigment genaamd beenhemoglobien (Lb). Dit is 'n suurstofvanger en hou verband met bloedpigment hemoglobien. Dit beskerm stikstofbindende ensiem stikstofase teen suurstof. Simbiotiese stikstofbinding vereis samewerking van Nod -gene van peulgewasse, knik, nif en herstel geengroepe van bakterieë.

Meganisme van stikstofbinding:

Stikstofbinding vereis (i) 'n verminderende krag soos NADPH, FMNH2 (ii) 'n bron van energie soos ATP (iii) ensiem di-nitrogenase en (iv) verbindings vir die vang van ammoniak wat gevorm word deur die reduksie van di-stikstof. Ensiemnitrogenase het yster en molibdeen. Beide van hulle neem deel aan die aanhegting van 'n molekule stikstof (N2).

Bindings tussen die twee stikstofatome word verswak deur hul binding aan die metaalkomponente. Die verswakte stikstofmolekule word deur waterstof (Fig. 12.13) van 'n verminderde koënsiem inwerk. Dit produseer dimied (N.2H2), hidrasien (N.2H4) en dan ammunisie en shynia (2NH3).

Ammoniak word nie bevry nie. Dit is giftig in selfs klein hoeveelhede. Die stikstofbinders beskerm hulself daarteen deur organiese sure te verskaf. Die reaksie tussen ammoniak en organiese sure veroorsaak aminosure.

N.5 + 8e – 8H + + 16ATP- di-stikstofase → 2NH3 + 2H + + 16 ADP + l6Pi

Ammoniak + α-ketoglutaraat + NAD(P)H- dehidrogenase → Glutamaat + NAD(P) + + H2O

Simbiotiese stikstofbindende organismes oorhandig 'n deel van hul vaste stikstof aan die gasheer in ruil vir skuiling en voedsel. Gratis lewende stikstofbinders verryk die grond nie onmiddellik nie. Dit is eers ná hul dood dat die vaste stikstof die fietsrypoel binnegaan. Dit vind plaas in twee stappe, ammonifikasie en nitrifikasie.

Dit word uitgevoer deur organismes wat deur verval veroorsaak word. Hulle werk op nitrog- en skynagtige uitskeidings en proteïene van lyke van lewende organismes, bv. Bacillus ramosus, B. vulgaris, B. mesentericus, Actinomyces. Proteïene word eers in aminosure opgebreek. Laasgenoemde word gedemineer. Organiese sure wat in die proses vrygestel word, word deur mikroörganismes vir hul eie metabolisme gebruik.

Ammoniak bly nie in die gasvormige toestand in die grond nie, maar word na ioniese vorm (NH+) verander. Dit kan direk deur plante gebruik word mits die pH van die grond meer as 6 is en die plant volop organiese sure bevat. Anders as nitrate, kan baie min plante ammoniumione stoor (bv. Begonia, Oxalis).

Dit is die verskynsel van omskakeling van ammonium stikstof na nitraat stikstof. Dit word in twee stappe uitgevoer - nitrietvorming en nitraatvorming. Beide die stappe kan deur Aspergillus flavus uitgevoer word. In die eerste stap word ammoniumione geoksideer tot nitriete Nitrosococcus, Nitrosomonas. Nitriete word in die tweede stap na nitrate verander, byvoorbeeld Nitrocystis, Nitrobacter.

Die meeste bakterieë wat nitrifikasie verrig (bv. Nitrosococcus, Nitrosomonas, Nitrobacter) is chemo -outotrofe. Hulle gebruik die energie wat tydens nitrifikasie vrygestel word in die sintese van organiese stowwe uit CO2 en 'n waterstofskenker. Dit is dus outotrofe wat nie sonenergie gebruik om voedsel te sintetiseer nie.

Onder anaërobiese toestande (bv. Waterlogging, suurstofuitputting) gebruik sommige mikroörganismes nitraat en ander geoksideerde ione as suurstofbron. In die proses word nitrate gereduseer tot gasvormige stikstofverbindings. Laasgenoemde ontsnap uit die grond. Algemene bakterieë wat de-nitrifikasie van grond veroorsaak, is Pseudomonas denitrificans, Thiobacillus denitrificans, Micrococcus denitrificans.

Stikstofoksiede wat in die atmosfeer ontsnap of gevorm word tydens abiologiese fiksasie kan ook afgebreek word deur aanvalle om molekulêre stikstof te vorm. De-nitrifikasie van grond put nie net die grond uit van 'n belangrike voedingstof nie, maar veroorsaak ook versuring wat ewe skadelik is in die oplosbaarheid van skadelike metale.

Nitraat Assimilasie:

Nitraat is die belangrikste bron van stikstof vir die plante. Dit kan in die selsap van verskeie plante ophoop en deelneem aan die osmotiese potensiaal. Dit kan egter nie as sodanig deur die plante gebruik word nie. Dit word eers verminder tot die vlak van ammoniak voordat dit in organiese verbindings opgeneem word. Die vermindering van nitraat vind in twee stappe plaas.

(i) Vermindering van nitraat tot nitriet:

Dit word uitgevoer deur die agentskap van 'n induseerbare ensiem genaamd nitraatreduktase. Die ensiem is 'n molibdoflavoproteïen. Dit benodig 'n herverkode koënsiem (NADH of NADPH) vir sy aktiwiteit. Die verminderde koënsiem word deur FAD of FMN met nitraat in aanraking gebring.

(ii) Vermindering van nitriet:

Dit word uitgevoer deur ensiem nitrietreduktase. Die ensiem is 'n metalloflavoproteïen wat koper en yster bevat. Dit kom binne -in chloroplaste in die bladselle en leukoplaste van ander selle voor. Daarteenoor word nitraatreduktase gevind wat los aan die selmembraan geheg is. Nitrietreduktase vereis verminderende krag.

Dit is NADPH in verligte selle en NADH in ander. Die proses van reduksie vereis ook ferredoksien wat in hoër plante meestal in groen weefsels voorkom. Daarom word daar aangeneem dat nitriet in hoër plante óf nitriet na blaarselle oorgaan, óf 'n ander elektrondonor (soos FAD) in onbelichte selle werk. Die produk van nitrietreduksie is ammoniak.

Ammoniak word nie bevry nie. Dit kombineer met sommige organiese sure om aminosure te produseer. Aminosure vorm dan verskillende tipes stikstofverbindings.

Sintese van Amino:

Die eerste organiese verbindings van stikstofassimilasie is ammunisiesure.

Hulle word gesintetiseer deur die volgende drie metodes:

1. Reduktiewe aminering:

In die teenwoordigheid van dehidrogenase (bv. Glutamaat dehidrogenase, Aspartaat dehidrogenase), 'n verlaagde koënsiem (NADH of NADPH), kan ammoniak direk gekombineer word met 'n keto-organiese suur soos a-ketoglutariensuur en oxaloazynsuur om aminosuur te vorm.

2. Katalitiese amidasie:

Ammoniak kombineer met katalitiese hoeveelhede glutamiensuur in die teenwoordigheid van ATP en ensiem glutaminesintetase. Dit produseer 'n amied genaamd glutamien. Glutamien reageer met a-ketoglutaric suur in die teenwoordigheid van ensiem glutamaat sintetase om twee molekules glutamaat te vorm. Verminderde ko-ensiem (NADH of NADPH) word vereis.

Dit is oordrag van aminogroepe (> CH NH2) van een aminosuur met die ketogroep (& gt С = О) van ketosuur. Die ensiem wat benodig word, is transaminase of aminotrans­ferase. Glutamienzuur is die primêre aminosuur wat betrokke is by die oordrag van die aminogroep (tot soveel as sewentien aminosure).

Dit is aminosuurderivate waarin – OH-komponent van karboksielgroep (- COOH) vervang word deur 'n ander aminogroep (- NH2). Amiede is dus dubbel geamineerde ketosure. Die twee mees algemene amiede is glutamien en asparagien.

Dit word gevorm deur middel van onderskeidelik glutamienzuur en asparagiensuur. Nog 'n algemene amied is vitamien niasien amied (niacien a). Glutamien en asparagien is komponente van proteïene saam met aminosure.

Die vorming daarvan vereis ATP-, ammoniak- en sintetase -ensiem (glutaminesintetase, asparagiensintetase). Amides vervul twee ander funksies: berging van oortollige stikstof en vervoer.


Die getypoel -scenario vir 'n oorsprong van polimere en repliserende chemie

In hierdie scenario konsentreer prebiotiese organiese monomere in getypoele in die hitte van 'n oerdag, gevolg deur polimerisasie deur dehidrasiesintese. Die vorming van polimeerverbindings is 'n 'opdraande' reaksie wat gratis energie benodig. Baie hoë temperature (die hitte van bak) kan monomere verbind deur dehidrasie sintese in die laboratorium, en het dit moontlik in getypoel sedimente gedoen om ewekansige polimere te vorm. Hierdie scenario veronderstel verder dat die verspreiding van hierdie polimere uit die getypoele met die eb en vloei van hoogwater. Die getypoel scenario word hieronder geïllustreer (Figuur 2).

Figuur 2: Getypoel scenario

Die konsentrasie van vermeende organiese monomere aan die onderkant van getypoele het moontlik geleenthede gebied om polimerisasie te kataliseer, selfs al is daar nie baie hoë hitte nie. Baie metale (nikkel, platinum, silwer, selfs waterstof) is anorganiese katalisators wat baie chemiese reaksies kan bespoedig. Die swaarder metale sou waarskynlik in die aardkors sowel as in die sedimente van oer-oseane bestaan, soos vandag. Daar is getoon dat sulke minerale aggregate in grond en klei katalitiese eienskappe besit. Verder is metale (bv. Magnesium, mangaan ...) nou 'n integrale deel van baie ensieme, in ooreenstemming met die oorsprong van biologiese katalisators in eenvoudiger saamgestelde minerale katalisators in oseanese sedimente.

Voor die lewe kon die mikro-oppervlaktes van mineraalverrykte sediment dieselfde, of ten minste soortgelyke reaksies, herhaaldelik kataliseer het, wat tot verwante stelle polimere gelei het. Oorweeg die moontlikhede vir RNA -monomere en polimere, gebaseer op die aanname dat lewe in 'n RNA -wêreld begin het. Die moontlikhede word hieronder in Figuur 3 geïllustreer.

Figuur 3: Repliserende polimere in 'n getypoel

Die resultaat wat hier voorspel word, is die vorming van nie net RNA-polimere nie (miskien eers kort), maar van H-gebonde dubbelstring-RNA-molekules wat effektief kan repliseer by elke siklus van konsentrasie, polimerisasie en verspreiding. Hitte en die vrye energie wat deur dieselfde reaksies vrygestel word, kon polimerisasie ondersteun het, terwyl katalise die getrouheid van RNA -replikasie sou verbeter het.

Natuurlik, in die getypoel -scenario, kan herhaalde hoë hitte of ander fisiese of chemiese aanval ook pas gevormde polimere afbreek. Maar wat as sommige RNA -dubbeldrade meer bestand was teen vernietiging? Sulke vroeë RNA -dupleks sal ophoop ten koste van die swakker, meer vatbare. Slegs die fiksste herhaalde molekules sal gekies word en in die omgewing bly! Die omgewingsophoping van struktureel verwante, repliseerbare en stabiele polimere weerspieël 'n prebiotiese chemikalie homeostase (een van daardie eienskappe van die lewe!)

Oor die algemeen hang hierdie scenario mooi saam, en het dit al vir baie dekades gedoen. Daar is egter nou uitdagende vrae oor die uitgangspunt van 'n prebiotiese verminderende omgewing. Nuwer bewyse dui op 'n aardatmosfeer wat glad nie verminder nie, wat twyfel laat ontstaan ​​oor die idee dat die eerste selle op die planeet heterotrofe was. Onlangse voorstelle stel alternatiewe bronne van prebiotiese vrye energie en organiese molekules voor wat heel anders lyk as dié van Oparin, Haldane, Urey en Miller.


Oorsprong van die lewe: Moderne teorie oor die oorsprong van lewe

Volgens hierdie teorie het lewe op die vroeë aarde ontstaan ​​deur fisies-chemiese prosesse van atome wat saamsmelt om molekules te vorm, wat molekules weer reageer om anorganiese en organiese verbindings te produseer. Organiese verbindings het 'n wisselwerking gehad om alle soorte makromolekules te produseer wat georganiseer was om die eerste lewende stelsel of selle te vorm.

Beeld met vergunning: upload.wikimedia.org/wikipedia/commons/6/6f/Blacksmoker_in_Atlantic_Ocean.jpg

Volgens hierdie teorie is 'lewe' dus spontaan op ons aarde afkomstig van nie-lewende materie. Eers word anorganiese verbindings en daarna organiese verbindings gevorm volgens die veranderende omgewingstoestande. Dit word chemiese evolusie genoem wat nie onder huidige omgewingstoestande op aarde kan plaasvind nie. Toestande wat geskik was vir die oorsprong van lewe, het slegs op primitiewe aarde bestaan.

Oparin-Haldane-teorie word ook chemiese teorie of naturalistiese teorie genoem. A. I. Oparin (1894-1980) was 'n Russiese wetenskaplike. Hy publiseer sy boek "The origin of Life" in 1936 en 'n Engelse uitgawe in 1938. J.B.S. Haldane (1892-1964) is in Engeland gebore, maar migreer in Julie 1957 na Indië en vestig hom in Bhubaneswar, Orissa. Hy was bioloog, biochemikus en genetikus. Beide Oparin (1938) en Haldane (1929) het soortgelyke sienings oor die oorsprong van lewe gegee.

Modeme sienings oor die oorsprong van lewe sluit in chemiese evolusie en biologiese evolusie:

A. Chemiese evolusie (chemogenie):

1. Die atoom fase:

Vroeë aarde het ontelbare atome van al daardie elemente gehad (bv. waterstof, suurstof, koolstof, stikstof, swael, fosfor, ens.) wat noodsaaklik is vir die vorming van protoplasma. Atome is in drie konsentriese massas geskei volgens hul gewigte, (a) die swaarste atome van yster, nikkel, koper, ens. Is in die middel van die aarde gevind, (b) mediumgewig atome van natrium, kalium, silikon, magnesium , aluminium, fosfor, chloor, fluoor, swael, ens. is in die kern van die aarde versamel, (c) Die ligste atome van stikstof, waterstof, suurstof, koolstof ens. het die primitiewe atmosfeer gevorm.

2. Vorming van anorganiese molekules:

Vrye atome gekombineer om anorganiese molekules soos H te vorm2 (Waterstof), N.2 (Stikstof), H.20 (Waterdamp), CH4 (Metaan), NH3 (Ammoniak), C02 (Koolstofdioksied). Waterstofatome was die meeste en die reaktiefste in die primitiewe atmosfeer.

Eerste waterstofatome het met alle suurstofatome gekombineer om water te vorm en geen vrye suurstof agter te laat nie. Primitiewe atmosfeer verminder dus die atmosfeer (sonder vrye suurstof) in teenstelling met die huidige oksiderende atmosfeer (met vrye suurstof).

Waterstofatome word ook gekombineer met stikstof, wat ammoniak vorm (NH3). Dus was water en ammoniak waarskynlik die eerste molekules van primitiewe aarde.

3. Vorming van eenvoudige organiese molekules (monomere):

Die vroeë anorganiese molekules het in wisselwerking getree en eenvoudige organiese molekules geproduseer soos eenvoudige suikers (bv. ribose, deoksiribose, glukose, ens.), stikstofbasisse (bv. puriene, pirimidiene), aminosure, gliserol, vetsure, ens.

Stormstortende reën het seker geval. Soos die water afgestorm het, moes dit opgelos het en soute en minerale saamgedra het, en uiteindelik in die vorm van oseane opgehoop het. So het antieke oseaniese water groot hoeveelhede opgeloste NH bevat3, CH4, HCN, nitriede, karbiede, verskillende gasse en elemente.

CH4 + C02 + H20 - & gt Suikers + Glycerol + Vetsure

CH4 + HCN + NH3 + H20 —> Puriene + Pirimidiene

Sommige eksterne bronne moes op die mengsel ingewerk het vir reaksies. Hierdie eksterne bronne kan (i) sonstraling wees, soos ultraviolet lig, X-strale, ens., (Ii) energie uit elektriese ontladings soos weerlig, (iii) hoë energie straling is ander bronne van energie (waarskynlik onstabiele isotope op die primitiewe aarde). Daar was geen osoonlaag in die atmosfeer nie.

'N Sopagtige sous van chemikalieë wat in die oseane van die vroeë aarde gevorm is, waarvan vermoedelik lewende selle verskyn het, word deur J.B. Haldane (1920)' prebiotiese sop 'genoem (ook' warm verdunde sop 'genoem). So was die verhoog vir die kombinasie van verskeie chemiese elemente. Sodra dit gevorm is, het die organiese molekules in water opgehoop omdat hul afbraak uiters stadig was in die afwesigheid van enige lewe of ensiem katalisators.

Eksperimentele bewyse vir abiogene molekulêre evolusie van lewe:

Stanley Miller in 1953, wat toe 'n gegradueerde was aan Harold Urey (1893-1981) aan die Universiteit van Chicago, het dit duidelik getoon dat ultravioletstraling of elektriese ontlading of hitte of 'n kombinasie hiervan komplekse organiese verbindings kan produseer uit 'n mengsel van metaan, ammoniak, water (waterstroom) en waterstof. Die verhouding van metaan, ammoniak en waterstof in Miller se eksperiment was 2:1:2.

Miller het vier gasse gesirkuleer—metaan, ammoniak, waterstof en waterdamp in ’n lugdigte apparaat en elektriese ontladings van elektrodes by 800°C deurgegee. Hy het die mengsel deur 'n kondensor gelei.

Hy sirkuleer die gasse op hierdie manier deurlopend vir een week en ontleed dan die chemiese samestelling van die vloeistof in die apparaat. Hy het 'n groot aantal eenvoudige organiese verbindings gevind, waaronder sommige aminosure soos alanien, glisien en asparaginsuur. Miller het die eksperiment uitgevoer om die idee te toets dat organiese molekules in 'n verminderende omgewing gesintetiseer kan word.

Ander stowwe, soos ureum, waterstofsianied, melksuur en asynsuur was ook teenwoordig. In 'n ander eksperiment het Miller die mengsel van die gasse op dieselfde manier gesirkuleer, maar hy het nie die elektriese ontlading geslaag nie. Hy kon nie die beduidende opbrengs van die organiese verbindings kry nie.

Later het baie ondersoekers 'n groot verskeidenheid organiese verbindings gesintetiseer, insluitend puriene, pirimidien's en eenvoudige suikers, ens. Dit word beskou dat die noodsaaklike 'boustene' soos nukleotiede, aminosure, ens. van lewende organismes dus kon gevorm het. op die primitiewe aarde.

4. Vorming van komplekse organiese molekules (makromolekules):

'N Verskeidenheid aminosure, vetsure, koolwaterstowwe, puriene en pirimidienbasisse, eenvoudige suikers en ander organiese verbindings wat in die ou seë opgehoop het. In die oeratmosfeer kon elektriese ontlading, weerlig, sonenergie, ATP en polifosfate die bron van energie wees vir polimerisasiereaksies van organiese sintese.

S.W. Fox van die Universiteit van Miami het getoon dat as 'n byna droë mengsel van aminosure verhit word, polipeptiedmolekules gesintetiseer word. Net so kan eenvoudige suikers polisakkariede vorm en vetsure kan saamvoeg om vette te produseer. Aminosure kan proteïene vorm as ander faktore betrokke was.

Dus, die klein eenvoudige organiese molekules wat saamgevoeg word om groot komplekse organiese molekules te vorm, bv. Aminosuur -eenhede wat saamgevoeg is om polipeptiede en proteïene te vorm, eenvoudige suiker -eenhede wat saamgevoeg word om polisakkariede, vetsure en gliserol te vorm, verenig om vette, suikers, stikstofbase en fosfate te vorm gekombineer in nukleotiede wat in die antieke oseane tot nukleïensure gepolimeriseer het.

Stikstofbasisse + Pentose Suikers + Fosfate - — — & gt Nukleotiede

Nukleotiede + Nukleotiede — — — – & gt Nukleïensure

Wat was die eerste RNA of proteïen?

Die RNA se eerste hipotese:

In the early 1980s three scientists (Leslia orgel, Francis Crick and Carl Woese) independently proposed the RNA World as the first stage in the evolution of life in which RNA catalysed all molecules necessary for survival and replication. Thomas Ceck and Sidney Altman shared Nobel Prize in chemistry in 1989 because they discovered that RNA can be both a substrate and an enzyme.

If the first cells used RNA as their hereditary molecule, DNA evolved from an RNA template. DNA probably did not evolve as a hereditary molecule un tills RNA based life became enclosed in membrane. Once cells evolved DNA probably replaced RNA as the genetic code for most organisms.

The Protein First Hypothesis:

A number of authors (for example Sidney Fox, 1978) claimed that a protein catalytic system must have developed before a nucleic acid replicative system. Sidney Fox had shown that amino acids polymerized abiotically when exposed to dry heat to form proteinoids.

Cairns-Smith’s Hypothesis:

It was proposed by Graham Caims-Smith, according to which both proteins and RNA originated at the same time.

Formation of Nucleoproteins:

The giant nucleoprotein molecules were formed by the union of nucleic acid and protein molecules. These nucleoprotein particles were described as free living genes. Nucleoproteins gave most probably the first sign of life.

B. Biological Evolution (Biogeny):

Conditions for the Origin of Life:

For origin of life, at least three conditions are needed.

(a) There must have been a supply of replicators, i.e., self-producing molecules.

(b) Copying of these replicators must have been subject to error through mutation.

(c) The system of replicators must have required a continuous supply of free energy and partial isolation from the general environment.

The high temperature in early earth would have fulfilled the requirement of mutation.

1. Protobionts or Protocells:

These are at least two types of fairly simple laboratory produced structures— Oparin’s coacervates and Fox’s microspheres which possess some of the basic prerequisites of proto cells.

Although these structures were created artificially, they point to the likelihood that non-biological membrane enclosures (proto cells) could have sustained reactive systems for at least short periods of time and led to research on the experimental production of membrane bound vesicles containing molecules, i.e., proto cells.

The first hypothesis was proposed by Oparin (1920). According to this hypothesis early proto cell could have been a coacervate. Oparin gave the term coacer­vates. These were non-living structures that led to the formation of the first living cells from which the more complex cells have today evolved.

Oparin speculated that a proto cell consisted a carbohydrates, proteins, lipids and nucleic acids that accumulated to form a coacervate. Such a structure could have consisted of a collection of organic macromolecules surrounded by a film of water molecules.

This arrangement of water molecules, although not a membrane, could have functioned as a physical barrier between the organic molecules and their surroundings. They could selectively take in materials from their sur­roundings and incorporate them into their structure.

Coacervates have been synthesized in the laboratory. They can selectively absorb chemicals from the surrounding water and incorpo­rate them into their structure. Some coacervates contain enzymes that direct a specific type of chemical reaction.

Because they lack a definite membrane, no one claims coacervates are alive, but they do exhibit some life like characters. They have a simple but persistent orga­nization. They can remain in solution for extended periods. They have the ability to increase in size.

An another hypothesis is that early proto cell could have been a microsphere. A microsphere is a non-living collection of organic macromolecules with double layered outer boundary. The term microsphere was given by Sydney Fox (1958-1964).

Sidney Fox demonstrated the ability to build microspheres from proteinoids. Proteinoids are protein like structures consisting of branched chains of amino acids. Proteinoids are formed by the dehydration synthesis of amino acids at a temperature of 180°C. Fox, from the University of Miami, showed that it is feasible to combine single amino acids into polymers of proteinoids. He also demonstrated the ability to build microspheres from these proteinoids.

Fox observed small spherical cell-like units that had arisen from aggregations of proteinoids. These molecular aggregates were called proteinoid microspheres. The first non-cellular forms of life could have originated 3 billion years back. They would have been giant molecules (RNA, Proteins, Polysaccharides etc.).

Microspheres can be formed when proteinoids are placed in boiling water and slowly allowed to cool. Some of the proteinoid material produces a double-boundary structure that encloses the microsphere. Although these walls do not contain lipids, they do exhibit some membrane like characteristics and suggest the structure of a cellular membrane.

Microspheres swell or shrink depending on the osmotic potential in the surrounding solution. They also display a type of internal movement (streaming) similar to that exhibited by cells and contain some proteinoids that function as enzymes. Using ATP as a source of energy, microspheres can direct the formation of polypeptides and nucleic acids. They can absorb material from the surrounding medium.

They have the ability of motility, growth, binary fission into two particles and a capacity of reproduction by budding and fragmentation. Superficially, their budding resembles with those of bacteria and fungi.

According to some investigators, microspheres can be considered first living cells.

2. Origin of Prokaryotes:

Prokaryotes were originated from proto cells about 3.5 billion years ago in the sea. The atmosphere was anaerobic because free oxygen was absent in the atmosphere. Prokaryotes do not have nuclear membrane, cytoskeleton or complex organelles. They divide by binary fission. Some of the oldest known fossil cells appear as parts of stromatolites. Stromatolites are formed today from sediments and photosynthetic prokaryotes (mainly filamentous cynobacteria— blue green algae).

3. Evolution of Modes of Nutrition:

The earliest prokaryotes presumably obtained energy by the fermen­tation of organic molecules from the sea broth in oxygen free atmosphere (reducing atmosphere). They required readymade organic material as food and thus they were heterotrophs.

Due to rapid increase in the number of heterotrophs the nutrient from sea water began to disappear and gradually exhausted. That led to the evolution of autotrophs. These organisms were capable of producing their own organic molecules by chemosynthesis or photosynthesis.

Drop in temperature stopped synthesis of organic molecules in the sea water. Some of the early prokaryotes got converted into chemoautotrophs which prepared organic food by using energy released during certain inorganic chemical reactions. These anaerobic chemoautotrophs were like present anaerobic bacteria. They released CO2 in die atmosfeer.

Evolution of chlorophyll molecule enabled certain protocells to utilize light energy and synthesize carbohydrates. These were anaerobic photoautotrophs. They did not use water as a hydrogen source. They were similar to present day sulphur bacteria in which hydrogen sulphide split into hydrogen and sulphur. Hydrogen was used in food manufacture and sulphur was released as a waste product.

Aerobic photoautotrophs used water as a source of hydrogen and carbon dioxide as source of carbon to synthesize carbohydrate in the presence of solar energy. The first aerobic photoautotrophs were cyanobacteria (blue green algae) like forms which had chlo­rophyll. They released oxygen in the atmosphere as the by product of photosynthesis. The main source of genetic variation was mutation.

As the number of photoautotrophs increased, oxygen was released in the sea and atmosphere. Free oxygen than reacted with methane and ammonia present in the primitive atmosphere and transformed methane and ammonia into carbon dioxide and free nitrogen.

The oldest fossil belonging to blue green algae, named Archaeospheroides barbertonensis which is 3.2 billion years old. Oxygen releasing prokaryotes first appeared at least 2.5 billion years ago.

4. Formation of Ozone Layer:

As oxygen accumulated in the atmosphere, the ultra­violet light changed some of oxygen into ozone.

The ozone formed a layer in the atmosphere, blocking the ultraviolet light and leaving the visible light as the main source of energy.

5. Origin of Eukaryotes:

The eukaryotes developed from primitive prokaryotic cells about 1.5 billion years ago. There are two views regarding the origin of eukaryotes.

According to Margulis (1970-1981) of Boston Uni­versity, some anaerobic predator host cells engulfed primitive aerobic bacte­ria but did not digest them. These aerobic bacteria established themselves inside the host cells as symbionts. Such preda­tor host cells became the first eukaryotic cells.

The predator host cells that engulfed aerobic bacteria evolved into animal cells while those that captured both aerobic bacteria and blue-green algae became eukaryotic plant cells. The aerobic bacteria established them­selves as mitochondria and blue green algae as chloroplasts.

(ii) Origin by Invagination:

Ac­cording to this view cell organelles of eukaryotic cells might have originated by invagination of surface membrane of primitive prokaryotic cells.


Although there is still no definitive answer, there is evidence that points to a likely scenario. Here are some of the most popular hypotheses for the origin of life on Earth.

Chemical evolution, or abiogenesis

In evolutionary biology, the term “chemical evolution” is used to refer to the hypothesis that says the building blocks of life, that is, aminosure, were formed through the combination of inorganic molecules.

Ook genoem abiogenesis, this is a well-known hypothesis for the origin of life on Earth.

Earth’s primitive atmosphere was quite hostile compared to today’s atmosphere. It was mostly composed of methane, hydrogen, water vapor, and ammonia.

In addition to containing almost no oxygen, the ozone layer that today protects us from deadly radiation from the Sun also did not exist. Consequently, ultraviolet rays were constantly hitting the Earth.

Taking into account that new atoms are only created in the core of stars or during supernovae explosions, all the atoms that exist on Earth today have been recycled for billions of years.

This leads us to two conclusions: either the elements that later gave rise to life were already on Earth when it was formed, or they came from outside, through meteors.

Within the hypothesis that inorganic elements were already on Earth, there are several other hypotheses about where on the planet the chemical evolution could have started.

The primordial soup

The idea that the mixture of gases present in the primitive atmosphere could create amino acids was proposed by scientists Oparin and Haldane in 1924.

They hypothesized that organic molecules could be created from inorganic molecules found on the ocean floor. However, they were unable to prove it.

In 1953, scientists Miller and Urey carried out an experiment that became known as “primordial soup”.

The experiment showed how amino acids could be created using only a few inorganic ingredients, in a controlled environment that mimicked conditions found on the primitive Earth.

Initially, the experiment was a success, yielding several other hypotheses about the composition of life. However, years later it was discovered that some of the elements of the primordial soup were not present in the primitive atmosphere.

Still, the theory was important in showing that organic molecules could be formed from inorganic elements with relative ease.

Related posts:

Hidrotermiese vents

Considering that the necessary inorganic elements were already on Earth, most theories agree that the transformation of inorganic molecules into organic ones started in the oceans.

The surface of the primitive Earth was also mostly covered by oceans, and the bottom of these oceans was protected from ultraviolet radiation. In addition, on the ocean floor, there are structures known as hydrothermal vents.

According to this hypothesis, these vents could have expelled hydrogen-rich molecules, which ended up accumulating in rocky corners, providing mineral catalysts for the reactions.

Even today, these extremely hot underwater areas are full of primitive life forms.

Life may have started because of lightning

In the Miller-Urey experiment, electrical sparks were used to generate amino acids from inorganic molecules, suggesting that lightning might have helped start life on Earth.

Volcanic clouds in the primitive atmosphere could contain methane, hydrogen, and ammonia. And being stimulated by lightning, these elements could have given rise to the first organic molecules.

A beginning under the ice

Another hypothesis suggests that life may have started under the ice. 3 billion years ago, the Sun was a third less bright than today, so the oceans were covered by ice.

This thick layer of ice could have protected the first organic compounds from ultraviolet radiation and meteor impacts.

The low temperature could also have helped the molecules to survive longer, giving enough time for important reactions to take place.

Related posts:

Panspermia: life from space

The panspermia hypothesis holds that primitive cells and amino acids arrived on Earth through meteors.

Unlike other hypotheses that try to explain how the building blocks of life originated from inorganic molecules, proponents of the panspermia hypothesis argue that life may have formed in space, and only then reached Earth.

This hypothesis would explain not only how life came about, but also how it spread across the globe.

One of the great advocates of this hypothesis was Stephen Hawking, one of the reasons behind his interest in space exploration.

Meteors that fall to Earth are always analyzed. En amino acids are commonly found in them, which reinforces this hypothesis, since these same compounds could have fallen into the primitive oceans, producing simple proteins and essential enzymes for the first prokaryotic cells on Earth.

Which of these hypotheses do you think is correct? Leave your thoughts in the comments below.


Process that might have led to first organic molecules

New research led by the American Museum of Natural History and funded by NASA identifies a process that might have been key in producing the first organic molecules on Earth about 4 billion years ago, before the origin of life. The process, which is similar to what might have occurred in some ancient underwater hydrothermal vents, may also have relevance to the search for life elsewhere in the universe. Details of the study are published this week in the journal Verrigtinge van die National Academy of Sciences.

All life on Earth is built of organic molecules -- compounds made of carbon atoms bound to atoms of other elements such as hydrogen, nitrogen and oxygen. In modern life, most of these organic molecules originate from the reduction of carbon dioxide (CO2) through several "carbon-fixation" pathways (such as photosynthesis in plants). But most of these pathways either require energy from the cell in order to work, or were thought to have evolved relatively late. So how did the first organic molecules arise, before the origin of life?

To tackle this question, Museum Gerstner Scholar Victor Sojo and Reuben Hudson from the College of the Atlantic in Maine devised a novel setup based on microfluidic reactors, tiny self-contained laboratories that allow scientists to study the behavior of fluids -- and in this case, gases as well -- on the microscale. Previous versions of the reactor attempted to mix bubbles of hydrogen gas and CO2 in liquid but no reduction occurred, possibly because the highly volatile hydrogen gas escaped before it had a chance to react. The solution came in discussions between Sojo and Hudson, who shared a lab bench at the RIKEN Center for Sustainable Resource Science in Saitama, Japan. The final reactor was built in Hudson's laboratory in Maine.

"Instead of bubbling the gases within the fluids before the reaction, the main innovation of the new reactor is that the fluids are driven by the gases themselves, so there is very little chance for them to escape," Hudson said.

The researchers used their design to combine hydrogen with CO2 to produce an organic molecule called formic acid (HCOOH). This synthetic process resembles the only known CO2-fixation pathway that does not require a supply of energy overall, called the Wood-Ljungdahl acetyl-CoA pathway. In turn, this process resembles reactions that might have taken place in ancient oceanic hydrothermal vents.

"The consequences extend far beyond our own biosphere," Sojo said. "Similar hydrothermal systems might exist today elsewhere in the solar system, most noticeably in Enceladus and Europa -- moons of Saturn and Jupiter, respectively -- and so predictably in other water-rocky worlds throughout the universe."

"Understanding how carbon dioxide can be reduced under mild geological conditions is important for evaluating the possibility of an origin of life on other worlds, which feeds into understanding how common or rare life may be in the universe," added Laurie Barge from NASA's Jet Propulsion Laboratory, an author on the study.

The researchers turned CO2 into organic molecules using relatively mild conditions, which means the findings may also have relevance for environmental chemistry. In the face of the ongoing climate crisis, there is an ongoing search for new methods of CO2 vermindering.

"The results of this paper touch on multiple themes: from understanding the origins of metabolism, to the geochemistry that underpins the hydrogen and carbon cycles on Earth, and also to green chemistry applications, where the bio-geo-inspired work can help promote chemical reactions under mild conditions," added Shawn E. McGlynn, also an author of the study, based at the Tokyo Institute of Technology.


Fuel for earliest life forms: Organic molecules found in 3.5 billion-year-old rocks

3.5 billion-year-old barite (bottom) with fossilized microbial mat (top). This barite is part of the Dresser Formation in NW Australia. Credit: Helge Missbach

A research team including the geobiologist Dr. Helge Missbach from the University of Cologne has detected organic molecules and gases trapped in 3.5-billion-year-old rocks. A widely accepted hypothesis says that the earliest life forms used small organic molecules as building materials and energy sources. However, the existence of such components in early habitats on Earth was as yet unproven. The current study, published in the journal Natuur kommunikasie, shows that solutions from archaic hydrothermal vents contained essential components that formed a basis for the earliest life on our planet.

Specifically, the scientists examined about 3.5-billion-year-old barites from the Dresser Formation in Western Australia. The barite thus dates from a time when early life developed on Earth. "In the field, the barites are directly associated with fossilized microbial mats, and they smell like rotten eggs when freshly scratched. Thus, we suspected that they contained organic material that might have served as nutrients for early microbial life," said Dr. Helge Missbach of the Institute of Geology and Mineralogy and lead author of the study.

In the fluid inclusions, the team identified organic compounds such as acetic acid and methanethiol, in addition to gases such as carbon dioxide and hydrogen sulfide. These compounds may have been important substrates for metabolic processes of early microbial life. Furthermore, they are discussed as putative key agents in the origin of life on Earth. "The immediate connection between primordial molecules emerging from the subsurface and the microbial organisms—3.5 billion years ago—somehow surprised us. This finding contributes decisively to our understanding of the still unclear earliest evolutionary history of life on Earth," Missbach concluded.


STEPS INVOLVED IN WRITING IUPAC NAME

1) The first step in giving IUPAC name to an organic compound is to select the parent chain and assign a word root.

2) Next, the appropriate primary suffix(es) must be added to the root word to indicate the saturation or unsaturation.

3) If the molecule contains functional group or groups, a secondary suffix must be added to indicate the main functional group. This is optional and not necessary if the molecule contains geen functional group.

4) Prefix the root word with the infix "cyclo" if the parent chain is cyclic or with the infix "spiro" if it is a spiro compound or with the infix "bicyclo" if the compound is bicyclic.

5) Finally add prefix(es) to the IUPAC name, if there are side chains or substituents on the parent chain.

Bv. The IUPAC name of the following compound (3-methylbutan-2-ol) is arrived in steps mentioned below.

Step-1 How many carbons are there in the parent chain? 4 Root word = "but"
Step-2 Saturated or Unsaturated? Saturated 1 o suffix = "ane"
Step-3 Is there any functional group? Ja. There is an alcohol group on 2nd carbon. 2 o suffix = "2-ol"
Step-4 Are there any side chains or substituents? Ja. There is a methyl group on 3rd carbon. 2 o prefix = "3-methyl"

Now add them to makeup the IUPAC name of the compound.

You will learn how to select a parent chain? how to number the carbon atoms and give the locants to the functional groups, side chains ? etc., in the following section.

RULES OF IUPAC NOMENCLATURE

The following IUPAC nomenclature rules are helpful in assigning the systematic IUPAC name of an organic compound.

1) The selection of parent chain:

The first step in naming an organic compound is to select the parent chain and give the root word based on the number of carbon atoms in it.

The parent chain in an organic molecule is the longest continuous carbon chain containing as many functional groups, double bonds, triple bonds, side chains and substituents as possible.

i) In the following molecule, the longest chain has 6 carbons. Hence the word root is "hex-". Note that the parent chain may not be straight.

ii) The root word for the following molecule is "hept-" since the longest chain contains 7 carbons.

Moenie come under the impression that the ethyl groups (-C2H5) are side chains and the longest chain contains 5 carbons.

The shaded part shows the longest chain that contains 7 carbons. Also look at the alternate way of writing this molecule in which the ethyl groups are expanded to -CH2CH3.

iii) In the following molecule, there are three chains of equal length (7 carbons).

However, the chain with more number of substituents (that with 3 substituents as shown in the following diagram) is to be taken as the parent chain. Thus "hept" appears as word root in the IUPAC name of this compound.

iv) The double bonds and triple bonds have more priority than the alkyl side chains and some other substituents like halo, nitro, alkoxy etc. Hence, whenever there are two or more chains with equal number of carbons, the chain that contains double or triple bond is to be selected as the parent chain irrespective of other chain containing more number of substituents.

There are two chains with 6 carbons. But the chain with the a double bond as shown in the diagram (II) is to be selected as the parent chain.

Note: The double bond has more priority than the triple bond.

v) However, the longest chain must be selected as parent chain irrespective of whether it contains multiple bonds or not.

Bv. In the following molecule, the longest chain (shaded) contains no double bond. It is to be selected as parent chain since it contains more carbons (7) than that containing double bond (only 6 carbons).

vi) The chain with main functional group must be selected as parent chain even though it contains less number of carbons than any other chain without the main functional group.

The functional group overrides all of above rules since it has more priority than the double bonds, triple bonds, side chains and other substituents.

Remember that the functional group is king.

Bv. The chain (shaded) with 6 carbons that includes the -OH functional group is to be selected as parent chain irrespective of presence of another chain with 7 carbons that contains no functional group.

There are other situations which will decide the parent chain. These will be dealt at appropriate sections.

2) Numbering the parent chain:

i) The positions of double bonds or triple bonds or substituents or side chains or functional groups on the parent chain are to be indicated by appropriate numbers (or locants). The locants are assigned to them by numbering carbon atoms in the parent chain.

Even though two different series of locants are possible by numbering the carbon chain from either sides, the correct series is chosen by following the rule of first point of difference as stated below.

Note: In iupac nomenclature, the number which indicates the position of the substituent is called 'locant'.

The rule of first point of difference:

When series of locants containing the same number of terms are compared term by term, that series which contains the lowest number on the occasion of the first difference is preferred.

For example, in the following molecule, the numbering can be done from either side of the chain to get two sets of locants. However the 2,7,8 is chosen since it has lowest number i.e., 2 on the first occasion of difference when compared with the other set: 3,4,9.

Actually the so called “Least Sum Rule” is the special case of above “Rule of First point of Difference”. Though looking simple, the least sum rule is valid only to chains with two substituents, a special case. However use of Least sum rule is not advisable when there are more than two substituents since it may violate the actual rule of first point of difference.

Therefore, while deciding the positions, we should always use "the rule of first point of difference" only.

ii) If two or more side chains are at equivalent positions, the one to be assigned the lower number is that cited first in the name.

In case of simple radicals, the group to be cited first in the name is decided by the alphabetical order of the first letter in case of simple radicals. While choosing the alphabetical order, the prefixes like di, tri, tetra must not be taken into account.

In the following molecule, 4-ethyl-5-methyloctane, both methyl and ethyl groups are at equivalent positions. However the ethyl group comes first in the alphabetical order. Therefore it is to be written first in the name and to be given the lowest number.

Note: The groups: sec-butyl and tert-butyl are alphabetized under "b". However the Isobutyl and Isopropyl groups are alphabetized under "i" and not under "b" or "p".

iii) However, if two or more groups are nie at equivalent positions, the group that comes first alphabetically may not get the least number.

Bv. In the following molecule, 5-ethyl-2-methylheptane, the methyl and ethyl groups are not at equivalent positions. The methyl group is given the least number according to the rule of first point of difference.

But note that the ethyl group is written first in the name.

iv) The multiple bonds (double or triple bonds) have higher priority over alkyl or halo or nitro or alkoxy groups, and hence should be given lower numbers.

Bv. In the following hydrocarbon, 6-methylhept-3-ene, the double bond is given the lower number and is indicated by the primary suffix 3-ene. The position of methyl group is indicated by locant, 6.

v) The double bond is preferred over the triple bond since it is to be cited first in the name.

Therefore the double bond is to be given the lower number whenever both double bond and triple bond are at equivalent positions on the parent chain.

Bv. In the following hydrocarbon, hept-2-en-5-yne, both the double and triple bonds are at equivalent positions. But the position of double bond is shown by 2-ene. The counting of carbons is done from the left hand side of the molecule.

vi) However, if the double and triple bonds are not at equivalent positions, then the positions are decided by the rule of first point of difference.

Bv. In the following hydrocarbon, hept-4-en-2-yne, the double and triple bonds are not at equivalent positions. The triple bond gets the lower number.

Again note that the 4-ene is written first.

vii) Nevertheless, the main functional group must be given the least number even though it violates the rule of first point of difference. It has more priority over multiple bonds also.

For example, in the following organic molecule, 6-methyloct-7-en-4-ol, the -OH group gets lower number (i.e., 4) by numbering the carbons from right to left.

3) Grammar to be followed in writing the IUPAC name:

i) The IUPAC name must be written as one word. Daar is egter uitsonderings.

ii) The numbers are separated by commas.

iii) The numbers and letters are separated by hyphens.

iv) If there are two or more same type of simple substituents they should be prefixed by di, tri, tetra, penta etc.

Bv. The number of methyl groups are indicated by di and tri in the following cases.

v) If the side chains themselves contain terms like di, tri, tetra etc., the multiplying prefixes like bis, tris, tetrakis etc., should be used.

Bv. The two 1,2-dimethylpropyl groups are indicated by the prefix "bis" as shown below.

vi) If two or more side chains of different nature are present, they are cited in alphabetical order.

* In case of simple radicals, they are alphabetized based on the first letter in the name of simple radical without multiplying prefixes.

Bv. In the following molecule, the ethyl group is written first since the letter 'e' precedes the letter 'm' of methyl in the alphabetical order. We should not compare 'e' in the word 'ethyl' and 'd' in the word 'dimethyl'

* However the name of a complex radical is considered to begin with the first letter of its complete name.

Bv. In the following case, “dimethylbutyl” is considered as a complete single substituent and is alphabetized under "d".


The First Organic Molecules

All living things consist of organiese molekules, centered around the element carbon. Therefore, it is likely that organic molecules evolved before cells, perhaps as long as 4 billion years ago. How did these building blocks of life first form?

Scientists think that lightning sparked chemical reactions in Earth’s early atmosphere. The early atmosphere contained gases such as ammonia, methane, water vapor, and carbon dioxide. Scientists hypothesize that this created a “soup” of organic molecules from inorganic chemicals. In 1953, scientists Stanley Miller and Harold Urey used their imaginations to test this hypothesis. They created a simulation experiment to see if organic molecules could arise in this way (see the figure below). They used a mixture of gases to represent Earth’s early atmosphere. Then, they passed sparks through the gases to represent lightning. Within a week, several simple organic molecules had formed.

Miller and Urey’s Experiment. Miller and Urey demonstrated that organic molecules could form under simulated conditions of early Earth. What assumptions were their simulation based upon?

Which Organic Molecule Came First?

Living things need organic molecules to store genetic information and to carry out the chemical work of cells. Modern organisms use DNA to store genetic information and proteins to catalyze chemical reactions. So, did DNA or proteins evolve first? This is like asking whether the chicken or the egg came first. DNA encodes proteins and proteins are needed to make DNA, so each type of organic molecule needs the other for its own existence. How could either of these two molecules have evolved before the other? Did some other organic molecule evolve first, instead of DNA or proteins?

RNA World Hypothesis

Some scientists speculate that RNA may have been the first organic molecule to evolve. In fact, they think that early life was based solely on RNA and that DNA and proteins evolved later. Dit word die RNA world hypothesis. Why RNA? It can encode genetic instructions (like DNA), and some RNAs can carry out chemical reactions (like proteins). Therefore, it solves the chicken-and-egg problem of which of these two molecules came first. Other evidence also suggests that RNA may be the most ancient of the organic molecules.


Kyk die video: 5V - BvJ Max - T3 - Stofwisseling (September 2022).