Name: eukaryotic dna copying at the replication fork
Uploaded: 2023-06-23T15:38:45.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

Georgia Standards of Excellence

9-12

Biology

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Replication in Eukaryotes

DNA replication in eukaryotic chromosomes initiates at multiple origins of replication, which are identified and bound by the origin recognition complex, or ORC.
The ORC then recruits helicases to unwind the DNA, producing a replication bubble with two replication forks.
The two forks move in opposite directions and disrupt the nucleosomes ahead of them. These nucleosomes are then reassembled on the daughter strands, maintaining the chromatin structure.
At each fork, RNA primers provide the site for DNA polymerase to elongate the leading strand and the Okazaki fragments of the lagging strand.
An RNase enzyme then removes these primers, and the DNA polymerase fills the gaps. Finally, DNA ligase seals the fragments together.
However, as the last primer is removed from the lagging strand at the end of the linear chromosome, it produces an overhanging stretch of the template DNA.
An enzyme called telomerase extends this overhanging stretch with non-coding DNA to prevent the loss of coding DNA during subsequent replication cycles.
The replication continues until the adjacent replication bubbles merge and the whole chromosome is duplicated.

replication in eukaryotes

In eukaryotische cellen is de DNA-replicatie in hoge mate geconserveerd en strak gereguleerd. Meerdere lineaire chromosomen moeten vóór de celdeling met hoge betrouwbaarheid worden gedupliceerd, dus er zijn veel eiwitten die een gespecialiseerde rol vervullen in het replicatieproces. Replicatie vindt plaats in drie fasen: initiatie, verlenging en beëindiging, en eindigt met twee volledige sets chromosomen in de kern.

Veel eiwitten orkestreren de replicatie bij de oorsprong

Eukaryotische replicatie volgt veel van dezelfde principes als prokaryotische DNA-replicatie, maar omdat het genoom veel groter is en de chromosomen lineair zijn in plaats van circulair, vereist het proces meer eiwitten en kent het een paar belangrijke verschillen. Ten eerste vindt replicatie bij eukaryoten, in tegenstelling tot prokaryoten, gelijktijdig plaats op meerdere replicatie-oorsprongen langs elk chromosoom. Initiatoreiwitten herkennen en binden zich aan deze oorsprong en recruteren helicase-eiwitten om de dubbele DNA-helix af te wikkelen. Op elk punt van oorsprong vormen zich twee replicatievorken. Primase voegt vervolgens korte RNA-primers toe aan de afzonderlijke DNA-strengen, die dienen als startpunt voor DNA-polymerase om te binden en de sequentie te kopiëren. DNA kan alleen in de 5'-naar-3'-richting worden gesynthetiseerd, dus de replicatie van beide strengen vanaf een enkele replicatievork verloopt in twee verschillende richtingen. De leidende streng wordt continu gesynthetiseerd, terwijl de achterblijvende streng wordt gesynthetiseerd in korte stukken van 100-200 basenparen lang, de zogenaamde Okazaki-fragmenten. Zodra het grootste deel van de replicatie voltooid is, verwijderen RNase-enzymen de RNA-primers, vult DNA-polymerase de gaten op en dicht DNA-ligase de gaten in de nieuwe streng af.

Het verdelen van het replicatiewerk over polymerasen

De werklast van het kopiëren van DNA in eukaryoten is verdeeld over meerdere verschillende soorten DNA-polymerase-enzymen. Grote families van DNA-polymerasen in alle organismen worden gecategoriseerd op basis van de gelijkenis van hun eiwitstructuren en aminozuursequenties. De eerste families die ontdekt werden, werden A, B, C en X genoemd, terwijl de families Y en D later werden geïdentificeerd. Familie B-polymerasen in eukaryoten omvatten Pol α, dat ook functioneert als een primase bij de replicatievork, en Pol δ en ε, de enzymen die het meeste werk van DNA-replicatie op respectievelijk de leidende en achterblijvende strengen van de matrijs doen. Andere DNA-polymerasen zijn verantwoordelijk voor taken als het repareren van DNA-schade, het kopiëren van mitochondriaal en plastide-DNA en het opvullen van gaten in de DNA-sequentie op de achterblijvende streng nadat de RNA-primers zijn verwijderd.

Telomeren beschermen de uiteinden van de chromosomen tegen afbraak

Omdat eukaryote chromosomen lineair zijn, zijn ze aan de uiteinden vatbaar voor afbraak. Om belangrijke genetische informatie tegen schade te beschermen, bevatten de uiteinden van chromosomen veel niet-coderende herhalingen van sterk geconserveerd G-rijk DNA, de telomeren. Een korte enkelstrengige 3'-overhang aan elk uiteinde van het chromosoom interageert met gespecialiseerde eiwitten, die het chromosoom in de kern stabiliseren. Vanwege de manier waarop de achterblijvende streng wordt gesynthetiseerd, kan een kleine hoeveelheid van het telomere DNA niet bij elke celdeling worden gerepliceerd. Als gevolg hiervan worden de telomeren in de loop van vele celcycli geleidelijk korter, en kunnen ze dus worden gemeten als een marker voor cellulaire veroudering. Bepaalde celpopulaties, zoals kiemcellen en stamcellen, brengen telomerase tot expressie, een enzym dat de telomeren verlengt, waardoor de cel meer celcycli kan ondergaan voordat de telomeren korter worden.

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before ...

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Replicatie in eukaryoten

eukaryotic dna copying at the replication fork

Eukaryotic DNA copying happens at replication forks, where the two DNA strands separate and new strands are built. This process lets a cell make an exact copy of its genetic material before it divides.

The transcript explains that eukaryotic replication follows the same basic steps seen in other DNA replication systems, but it takes place in cells with a nucleus. The replication machinery works on each separated strand as a template, so the new DNA matches the original sequence.

This topic is important for high school biology because it connects DNA structure to cell division and inheritance. Understanding replication in eukaryotes helps students see how genetic information is passed on when body cells grow and reproduce.

Eukaryotic DNA Copying at the Replication Fork

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Eukaryotic DNA copying happens at replication forks, where the two DNA strands separate and new strands are built. This process lets a cell make an exact copy of its genetic material before it divides. The transcript explains that eukaryotic replication follows the same basic steps seen in other DNA replication systems, but it takes place in cells with a nucleus. The replication machinery works on each separated strand as a template, so the new DNA matches the original sequence. This topic is...

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key terms and concepts

Learn how eukaryotic DNA is copied at replication forks, where strands separate and new DNA is built before cell division in nucleus-containing cells.

Eukaryotic DNA Copying at the Replication Fork | JoVE K12

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Eukaryotic DNA Copying at the Replication Fork

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