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

SB2.a

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 eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
Many Proteins Orchestrate Replication at the Origin
Eukaryotic replication follows many of the same principles as prokaryotic DNA replication, but because the genome is much larger and the chromosomes are linear rather than circular, the process requires more proteins and has a few key differences. First, unlike prokaryotes, replication in eukaryotes occurs simultaneously at multiple origins of replication along each chromosome. Initiator proteins recognize and bind to these origins and recruit helicase proteins to unwind the DNA double helix. At each point of origin, two replication forks form. Primase then adds short RNA primers to the single strands of DNA, which serve as a starting point for DNA polymerase to bind and begin copying the sequence. DNA can only be synthesized in the 5&#39;&#160;to 3&#39;&#160;direction, so replication of both strands from a single replication fork proceeds in two different directions. The leading strand is synthesized continuously, while the lagging strand is synthesized in short stretches of 100&#8211;200 base pairs in length, called Okazaki fragments. Once the bulk of replication is complete, RNase enzymes remove the RNA primers, DNA polymerase fills the gaps, and DNA ligase seals the gaps in the new strand.
Dividing the Work of Replication Among Polymerases
The workload of copying DNA in eukaryotes is divided among multiple different types of DNA polymerase enzymes. Major families of DNA polymerases across all organisms are categorized by the similarity of their protein structures and amino acid sequences. The first families to be discovered were termed A, B, C, and X, with families Y and D identified later. Family B polymerases in eukaryotes include Pol &#945;, which also functions as a primase at the replication fork, and Pol &#948; and &#949;, the enzymes that do most of the work of DNA replication on the leading and lagging strands of the template, respectively. Other DNA polymerases are responsible for such tasks as repairing DNA damage, copying mitochondrial and plastid DNA, and filling in gaps in the DNA sequence on the lagging strand after the RNA primers are removed.
Telomeres Protect the Ends of the Chromosomes from Degradation
Because eukaryotic chromosomes are linear, they are susceptible to degradation at the ends. To protect important genetic information from damage, the ends of chromosomes contain many non-coding repeats of highly conserved G-rich DNA, the telomeres. A short single-stranded 3&#39;&#160;overhang at each end of the chromosome interacts with specialized proteins, which stabilize the chromosome within the nucleus. Because of the manner in which the lagging strand is synthesized, a small amount of the telomeric DNA cannot be replicated with each cell division. As a result, the telomeres gradually get shorter over the course of many cell cycles, and thus can be measured as a marker of cellular aging. Certain populations of cells, such as germ cells and stem cells, express telomerase, an enzyme that lengthens the telomeres, allowing the cell to undergo more cell cycles before the telomeres shorten.

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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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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