Kaučuk — разлика између измена

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== Hemijska struktura ==
[[File:NatVsSynPolyisoprene.png|thumb|upright=1.8|Hemijska struktura cis-poliizoprena, glavnog konstituenta prirodne gume. Sintetički cis-poliizopren i prirodni cis-poliizopren su izvedeni iz različitih prekursora, [[izopentenil pirofosfat]]a i [[izopren]]a.]]
{{rut}}
Lateks je polimer cis-1,4-poliizoprena – sa [[molecular weight|molekulskom težinom]] od 100.000 do 1.000.000 [[Dalton (unit)|daltona]]. Typically, a small percentage (up to 5% of dry mass) of other materials, such as [[proteins]], [[fatty acids]], [[resins]], and inorganic materials (salts) are found in natural rubber. Polyisoprene can also be created synthetically, producing what is sometimes referred to as "synthetic natural rubber", but the synthetic and natural routes are different.<ref name=Ullmann/> Some natural rubber sources, such as [[gutta-percha]], are composed of trans-1,4-polyisoprene, a [[structural isomer]] that has similar properties.
 
Lateks je polimer cis-1,4-poliizoprena – sa [[molecular weight|molekulskom težinom]] od 100.000 do 1.000.000 [[Dalton (unit)|daltona]]. Tipično, mali procenat (do 5% suve mase) drugih materijala, kao što su [[protein]]i, [[masna kiselina|masne kiseline]], [[rezin]]i, i neorganski materijali (soli) je prisutan u prirodnoj gumi. Poliizopren isto tako može da bude formiran sintetičkim putem, čime nastaje ono što se ponekad naziva „sintetičkom prirodnom gumom”. Sintetički i prirodni pristupi sintezi su različiti.<ref name=Ullmann/> Neki prirodni izvori gume, kao što je [[gutta-percha|gutaperča]], se sastoje od trans-1,4-poliizoprena, [[structural isomer|strukturnog izomera]] koji ima slična svojstva.
Natural rubber is an elastomer and a [[thermoplastic]]. Once the rubber is vulcanized, it is a [[thermoset]]. Most rubber in everyday use is vulcanized to a point where it shares properties of both; i.e., if it is heated and cooled, it is degraded but not destroyed.
 
Prirodna guma je elastomer i [[thermoplastic|termoplastika]]. Kada se guma vulkanizira, ona postaje [[Thermosetting polymer|reaktoplast]]. Većina guma u svakodnevnom životu je vulkanizirana do stepena u kome ima oba svojstva; i.e., ako se zagreva i hladi, ona se degradira ali ne biva uništena.
The final properties of a rubber item depend not just on the polymer, but also on modifiers and fillers, such as [[carbon black]], [[factice]], whiting and others.
 
Finalna svojstva gumenog predmeta ne zavise samo od polimera, nego i od modifikatora i punilaca, kao što je [[carbon black|čađ]], [[factice|faktis]] i drugi.
 
=== Biosinteza ===
 
RubberČestice particlesgume arese formedformiraju in theu [[cytoplasm|citoplazmi]] ofspecijalizovanih specializedćelija latex-producingunutar cellsbiljke calledkoje stvaraju lateks, zvanih [[laticifer|mlečnice]]s within rubber plants.<ref>{{cite book |editor-last= Koyama |editor-first= Tanetoshi |editor2-last= Steinbüchel |editor2-first= Alexander |chapter= Biosynthesis of Natural Rubber and Other Natural Polyisoprenoids |title= Polyisoprenoids |chapter-url={{google books |plainurl=y |id=1a_wAAAAMAAJ|page=73}}|series= Biopolymers |volume= 2 |publisher= Wiley-Blackwell |date= June 2011 |pages= 73–81 |isbn= 978-3-527-30221-5 }}</ref> Rubber particles areČestice surroundedgume bysu aokružene singlejednoslojnom [[phospholipidfosfolipid]]nom membranemembranom withsa [[hydrophobichidrofob]]nim tailsrepovima pointedusmerenim inwardka unutrašnjosti. TheMembrana membraneomogućava allowsbiosintetičkim biosyntheticproteinima proteinsda tobudu besekvesterani sequesteredna atpovršinu therastućih surfacečestica of the growing rubber particlegume, whichšto allowsomogućava newdodavanje monomericnovih unitsmonomernih tojedinica besa addedspoljašnjosti from outside the biomembranemembrane, but withinali theunutar lacticifermlečnice. TheČestica rubbergume particleje isenzimatski anaktivan enzymaticallyentitet activekoji entitysadrži thattri containssloja three layers of materialmaterijala, the rubbergumenu particlečesticu, abiomembranu biomembranei andslobodne freemonomerne monomeric unitsjedinice. TheBiomembrana biomembraneje isčvrsto heldpripijena tightlyuz togumenu thesrž rubberusled corevisokog duenegativnog tonaelektrisanja theduž highdvostrukih negativeveza charge along the double bonds of the rubberosnove polymergumenog backbonepolimera.<ref>{{cite journal |last1= Paterson-Jones |first1= J.C. |last2= Gilliland |first2= M.G. |last3= Van Staden |first3= J. |title= The Biosynthesis of Natural Rubber |journal= Journal of Plant Physiology |volume= 136 |issue= 3 |pages= 257–263 |date= June 1990 |doi= 10.1016/S0176-1617(11)80047-7 |issn= 0176-1617}}</ref> FreeSlobodne monomericmonomerne unitsjedinice andi conjugatedkonjugovani proteinsproteini makesačinjavaju upspoljašnji the outer layersloj. ThePrekurzor rubbergume precursor isje [[isopentenylizopentenil pyrophosphatepirofosfat]] (anjedno [[Allyl group|allylicalilno]] compoundjedinjenje), whichkoje elongatesse byprodužava pomoću -{Mg}-<sup>2+</sup>-dependentzavisne condensationkondenzacije byposredstvom thegumene action of rubber transferasetransferaze. TheMonomer monomerse addsdodaje tona the pyrophosphate end ofpirofosfatni thekraj growingrastućeg polymerpolimera.<ref>{{cite book |first1=Christian |last1=Schulze Gronover |first2=Daniela |last2=Wahler |first3=Dirk |last3=Prufer |editor-last= Magdy |editor-first= Elnashar |date=5 Jul 2011 |title=Biotechnology of Biopolymers |chapter=4. Natural Rubber Biosynthesis and Physic-Chemical Studies on Plant Derived Latex |isbn= 978-953-307-179-4 |chapter-url=http://www.intechopen.com/books/biotechnology-of-biopolymers/natural-rubber-biosynthesis-and-physic-chemical-studies-on-plant-derived-latex}}</ref> TheOvim processprocesom displacesse thezamenjuje terminalterminalni high-energyvisokoenergetski pyrophosphatepirofosfat. The reaction producesReakcija aproizvodi cis polymerpolimer. TheKorak initiationuvođenja stepmonomera isje catalyzed bykatalizovan [[prenyltransferase|preniltransferazom]], whichkoja convertskonvertuje threetri monomers ofmonomera isopentenylizopentenil pyrophosphatepirofosfata intou [[farnesylfarnezil pyrophosphatepirofosfat]].<ref>{{cite journal |last1= Xie |first1= W. |display-authors= 3 |last2= McMahan |first2= C.M. |last3= Distefano |first3= A.J. DeGraw, M.D. |last4= Cornish |first4= K. |last5= Whalen |first5= M. C. |last6= Shintani |first6= D.K. |date= 2008 |title= Initiation of rubber synthesis: In vitro comparisons of benzophenone-modified diphosphate analogues in three rubber preducing species |journal= Phytochemistry |volume= 69 |issue= 14 |pages= 2539–2545 |doi= 10.1016/j.phytochem.2008.07.011 |pmid=18799172}}</ref> TheFarnezil farnesylpirofosfat pyrophosphatese canmože bindvezati toza rubbertransferazu transferasegume toradi elongateprodužavanja arastućeg new rubbergumenog polymerpolimera.
 
TheNeophodni requiredizopentenil isopentenylpirofosfat pyrophosphatese isdobija obtained from theiz [[mevalonatemevalonat]]nog pathwayputa, whichgde derivesje fromizveden iz [[acetyl-CoA|acetil-KoA]] in theu [[cytosolcitosol]]u. InU plantsbiljkama, isopreneizopren pyrophosphatepirofosfat canse alsoisto betako obtainedmože fromdobiti theiz 1-deoxdeoks-D-xyuloseksiluloza-5-phosphatefosfat/2-C-methylmetil-D-erythritoleritritol-4-phosphatefosfat pathwayputa withinunutar plasmidsplazmida.<ref>{{cite journal |last1= Casey |first1= P.J. |last2= Seabra |first2= M.C. |date= 1996 |title= Protein Prenyltransferases |journal= Journal of Biological Chemistry |volume= 271 |issue= 10 |pages= 5289–5292 |doi= 10.1074/jbc.271.10.5289 |pmid=8621375}}</ref> TheRelativni relativeodnos ratiofarnezil ofpirofosfat theinicijatorske farnesyljedinice pyrophosphatei initiatorizoprenil unitpirofosfat andelongacionog isoprenylmonomera pyrophosphateodređuje elongationodnos monomerbrzine determinessinteze thenovih ratečestica ofu newodnosu particlena synthesis versus elongation ofproduživanje existingpostojećih particlesčestica. ThoughMada rubberje ispoznato knownda toje besinteza producedgume byposredovana onlysamo onejednim enzymeenzimom, extractsekstrakti oflateksa latexsadrže hostbrojne numerousproteine smallmale molecularmolekulske weightmase proteinsnepoznate withfunkcije. unknownPretpostavlja function.se Theda proteinsti possiblyproteini servesluže askao cofactorskofaktori, asjer se brzina thesinteze syntheticumanjuje ratekad decreasesse withoni completepotpuno removaluklone.<ref>{{cite journal |last1= Kang |first1= H. |last2= Kang |first2= M.Y. |last3= Han |first3= K.H. |date= 2000 |title= Identification of Natural Rubber and Characterization of Biosynthetic Activity |journal= Plant Physiol |volume= 123 |issue= 3 |pages= 1133–1142 |doi= 10.1104/pp.123.3.1133|pmid= 10889262 |pmc= 59076 }}</ref>
 
== Reference ==
Преузето из „https://sr.wikipedia.org/wiki/Kaučuk