Domov Technika Genom

Genom



Úvod

V oblastech molekulární biologie a genetiky se genomer vztahuje k souhrnnému genetickému materiálu fanorganismu. Tyto genetické materiály zahrnují DNA nebo RNA (virální RNA).

GenomickáDNAzahrnuje kódujícíDNAa nekódujícíDNA,mitochondriálníDNAachloroplastovouDNA.

Thetermgenomewascreatedin1920byHansWinkler,professorofbotanyattheUniversityofHamburg,Germany.

Věda o studiu genomu se nazývá genomika.

Klasifikace

Viralgenom

Virální genom může být složen z RNA nebo DNA. Genomeof RNA viru obsahuje jednovláknovou nebo dvouvláknovou RNA a také jednu nebo více jednotlivých molekul RNA. úhlově lineární molekuly DNA, ale některé jsou složeny z virových genomů DNA složených z kruhových molekul DNA.

Prokaryoticgenome

ThegenomesofprokaryotesandeukaryotesarecomposedofDNA.ArchaeahaveaDNAgenomecomposedofcircularchromosomes.Mostbacteriaalsohaveacircularchromosome,however,somebacterialspeciescontainlinearchromosomesormultiplechromosomes.ThegenomesofmostprokaryotesdonotcontainrepetitiveDNA.Somesymbioticbacterialgenomespeciescontainahighproportionofpseudogenes.Forexample,Serratiasymbioticagenomespecieshasonlyabout40%ofitsDNAencodingproteins.Somebacterialgenomesalsocontainauxiliarygeneticmaterial,whichispresentinplasmids.Forthisreason,thetermgenomeshouldnotbeusedasasynonymforchromosome.

Theeukaryoticgenome

TheeukaryoticgenomeconsistsofoneormorelinearDNAchromosomes.Thenumberofchromosomesthatmakeupthegenomeofeukaryotesvariesgreatly.Jackjumperantsandasexualnematodeshaveonlyonepairofchromosomeseach,whilefernspecieshave720pairsofchromosomes.Humancellshave22pairsofautosomesand1pairofsexchromosomes.

Inadditiontothechromosomesinthenucleus,eukaryoticorganellessuchaschloroplastsandmitochondriahavetheirownDNAandchromosomes.Therefore,therearealsotheterms"mitochondrialgenome"and"plastidgenome".Likethebacteriafromwhichtheyoriginate,bothmitochondriaandchloroplastscontaincircularchromosomes.

Differentfromprokaryotes,eukaryoteshaveexon-intronorganizationofprotein-codinggenesandacertainamountofrepetitiveDNA.ThemajorityofmammalianandplantgenomesarecomposedofrepetitiveDNA.

Posloupnost kódování

TheDNAsequencethatcarriesthegeneticinformationofthesyntheticproteinisthecodingsequence.Theproportionofcodingsequencesinthegenomevariesgreatlyindifferentspecies.Largergenomesdonotnecessarilycontainmoregenes,andtheproportionofnon-repetitiveDNAincomplexeukaryotesdecreasesasthesizeofthegenomeincreases.SimpleeukaryotessuchasCaenorhabditiselegansandDrosophilahaveahigherproportionofcodingDNAthanrepetitiveDNA,whilethegenomesofmorecomplexeukaryotesareoftencomposedofrepetitiveDNA.TheproportionofrepeatedDNAinthegenomesofsomeplantsandamphibiansexceeds80%.Similarly,only2%ofthehumangenomeencodesDNA.

Nekódovací sekvence

Non-codingsequencesincludeintrons,non-codingRNAsequences,regulatoryDNAandrepetitiveDNA.98%ofthehumangenomebelongstonon-codingsequences.TherepetitiveDNAofthegenomehastandemrepetitivesequencesandscatteredrepetitivesequences.

Transpozony

Transposons(TEs)areDNAsequenceswithaspecificstructure.Theycanmovearoundthegenomewithoutafixedposition.ClassITEjumpsthroughthecopyandpastemechanism,andClassIITEisexcisedfromthegenomeandinsertedintoanewposition.

ThemovementofTEisthedrivingforcefortheevolutionofeukaryoticgenomes,becausetheirinsertioncandestroygenefunction,homologousrecombinationbetweenTEscanleadtogeneduplication,andTEcanalsocombineexonswithTheadjustmentsequenceisreorganizedtoanewposition.

Retrotranspozony

Retrotranspozony lze přepsat do RNA a poté zkopírovat do genomu na jiné místo. Retrotranspozony lze rozdělit do dvou kategorií: dlouhodobé opakování (LTR) a dlouhodobé opakování (bez LTR).

Velikost genomu

Velikost genomu je celkový počet párů bází DNA v kopii haploidgenomu.

Genomesizeispositivelycorrelatedwiththemorphologicalcomplexityofprokaryotesandlowereukaryotes.However,aftermollusksandallotherhighereukaryotesmentionedabove,thiscorrelationnolongerexists,mainlybecauseofrepeatedDNA.

Genomechanges

Allcellsoftheorganismarederivedfromthesamesinglecell,sotheyshouldhavethesamegenome.However,insomecases,differencescanoccurbetweencells.BothDNAreplicationduringcelldivisionandtheactionofenvironmentalmutagenscancausemutationsinsomaticcells.Insomecases,suchmutationscancausecancerbecausetheycausecellstodividefasterandinvadesurroundingtissues.Duringmeiosis,diploidcellsdividetwicetoproducehaploidgermcells.Inthisprocess,recombinationcausesthegeneticmaterialtobereshuffledfromhomologouschromosomes,soeachgametehasauniquegenome.

Genomeevolution

Thegenomeisnotonlythesumofthegenesoftheorganism,thegenomealsocontainsothercharacteristicsthatcanbeconsideredforspecificgenesandtheirproducts.

Replicationplaysanimportantroleintheshapingofthegenome.Thescopeofreplicationincludestheextensionofshorttandemrepeats,thereplicationofgeneclusters,thereplicationofentirechromosomesandeventheentiregenome.Thisduplicationmaybethebasisforthecreationofnewgenetictraits.

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