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samenvatting celmobi: Hoofdstuk 15: Transcriptie

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samenvatting celmobi: Hoofdstuk 15: Transcriptie

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  • December 21, 2021
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  • 2021/2022
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Hoofdstuk 15: Transcriptie
• Centrale dogma v/d moleculaire biologie: informatiestroom cel = DNA – RNA – Eiwit




• DNA kan ook ander DNA maken (DNA-polymerasen)
• RNA:
→ Via transcriptie overgeschreven van DNA
→ Brengt info van nucleus naar cytoplasma (mRNA)
→ Soms eindproduct zoals rRNA, tRNA, snRNA,…
→ Verschillen met DNA:
▪ Suiker is ribose (<-> 2-desoxiribose)
▪ Uracil <-> thymine
▪ Meestal enkelstrengig
▪ Kan zeer verschillende structuren vormen
→ Synthese:
▪ Opgebouwd van 5’ → 3’ (template afgelopen van 3’ → 5’)
▪ OH-groep gebruikt via fosfordiesterverbinding nucleotide in te bouwen Gelijkenissen met
▪ Basenpaarcomplementariteit bepaalt de volgende base DNA-synthese
▪ Nucleotidetrifosfaten als bouwsteen (afsplitsing 2 fosfaten)
▪ Ribonucleotiden ingebouwd (<-> desoxiribonucleotiden)
▪ Slechts 1 DNA streng wordt afgelezen1 (template = coderend)
▪ Transcript = sense-RNA molecule Verschillen met
▪ Complementaire streng = antisense streng (= non-template) DNA-synthese
▪ Geen nood aan primer om te starten
▪ Geen proofreading, geen nuclease-eiwit
• RNA-polymerase:
→ 2 α, 2 β, 1 verwante β’ en 1 σ-polypeptide (=’holo’-enzym) Verschillende rol bij
→ ‘Core’-enzym: geen σ-sub-eenheid transcriptie
• Transcriptieproces bij E. coli:
→ Initiatie:
▪ RNA-polymerase2 herkent startsequentie = promotor3
⤷ Asymmetrisch => bepaalt richting
transcriptie en dus ook template
▪ Consensus-sequentie: meest voorkomende sequentie op specifieke positie in een
functioneel DNA-segment
→ -35 box: promotor-consensus
→ -10 box: hier opent RNA-polymerase de DNA-duplex om transcript te beginnen
vanaf +1 (= TATA-box)
▪ Vorming gesloten promotorcomplex (binding polymerase)


1
Naargelang het gen wordt ofwel de ene ofwel de andere streng afgelezen
2
Zorgt voor openen DNA-duplex, complementaire basenparing en terminatie reactie
3
Promotoren waarop polymerase in alle omstandigheden kan binden = constitutief (<-> gereguleerde)
Sterke promotoren = polymerase heeft hoge affiniteit => veelvuldige start van transcriptie (<-> zwakke)

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