Name: eukaryotic dna replication steps
Uploaded: 2023-04-30T11:44:02.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Biology

heredity-inheritance-and-variation-of-traits

Heredity- Inheritance and Variation of Traits

LS.Bio.6.2

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 ...

Education

JoVE Core

Cell Biology

Unit 1

DNA Replication and Repair

KEY TERMS AND CONCEPTS

eukaryotic dna replication steps

Eukaryotic DNA replication copies the genome before cell division. It happens in a tightly regulated way so each daughter cell gets a complete set of chromosomes in the nucleus. The process has three stages: initiation, elongation, and termination.

Eukaryotic cells use many proteins to manage replication because their chromosomes are linear and their genomes are larger than those of prokaryotes. Replication begins at multiple origins of replication along each chromosome. Initiator proteins bind to these origins and recruit helicase, which unwinds the DNA double helix. At each origin, two replication forks form.

Primase adds short RNA primers to the exposed DNA strands. These primers give DNA polymerase a starting point to copy the sequence. DNA is synthesized only in the 5' to 3' direction, so the two strands are copied in different ways. The leading strand is made continuously. The lagging strand is made in short pieces called Okazaki fragments, which are about 100 to 200 base pairs long. After most copying is finished, RNase removes the RNA primers. DNA polymerase fills the gaps, and DNA ligase seals the new strand.

Several DNA polymerases share the work in eukaryotic cells. These enzymes are grouped into families based on protein structure and amino acid sequence. The first families identified were A, B, C, and X, and families Y and D were found later. In eukaryotes, family B includes Pol alpha, which also acts as a primase at the replication fork, and Pol delta and Pol epsilon, which do most of the DNA copying on the lagging and leading strands, respectively. Other polymerases help repair DNA damage, copy mitochondrial and plastid DNA, and fill gaps left after RNA primer removal.

Eukaryotic chromosomes also need protection at their ends. Their tips contain telomeres, which are non-coding repeats of G-rich DNA. A short single-stranded 3' overhang at each end interacts with specialized proteins that help stabilize the chromosome in the nucleus. Because lagging strand synthesis leaves a small section of telomeric DNA uncopied each cycle, telomeres gradually shorten over many cell divisions. This shortening can serve as a marker of cellular aging. Some cells, including germ cells and stem cells, express telomerase, an enzyme that lengthens telomeres and allows more rounds of division before shortening occurs.

Eukaryotic DNA Replication Steps

base-pairing and dna repair

DNA Pairing Rules in Repair

DNA pairing rules help guide DNA repair. In DNA, bases pair in a specific way, and those matching pairs support accurate copying and fixing of the molecule. When DNA is damaged or copied incorrectly, repair systems can use the normal base-pairing pattern as a reference. This helps cells find mismatched bases and restore the correct sequence. The process depends on the idea that each base has a preferred partner. Understanding base-pairing is important because it explains how cells protect...

the dna replication fork

DNA Replication Fork in Action

The DNA replication fork is the active region where DNA copies itself. It forms when the two strands of the double helix separate so each strand can serve as a template for a new partner strand. At the fork, the copying process moves in a set direction. The two strands are built in different ways as replication continues, so the fork helps organize how the new DNA is made. The replication fork is a key part of accurate DNA duplication. It shows how the cell opens the double helix, copies the...

lagging strand synthesis

Okazaki Fragments on the Lagging Strand

Lagging strand synthesis builds new DNA in short pieces called Okazaki fragments. This happens during DNA replication because the lagging strand runs in the opposite direction from the direction the replication machinery moves. As the DNA double helix opens, DNA polymerase adds nucleotides only in the 5' to 3' direction. On the lagging strand, this forces the cell to copy the template in segments instead of one continuous stretch. Each segment begins near the replication fork and extends away...

the replisome

Replisome Components in DNA Copying

The replisome is the protein machine that copies DNA during cell division. It works at the replication fork, where the double helix opens so new strands can be made. DNA polymerase is the core enzyme in the replisome. It adds nucleotides to the growing DNA strand. In bacteria, two DNA polymerases work together at the fork. These enzymes are linked to the helicase by a clamp-like protein so they stay attached to the DNA. Helicase unwinds the DNA ahead of the fork. Single-stranded binding...

proofreading

DNA Polymerase Error Correction

DNA polymerase uses proofreading to help correct errors during DNA replication. As it builds the daughter strand, the enzyme adds nucleotides that match the template DNA strand. This matching helps keep DNA copying accurate and supports replication fidelity. DNA is made in the 5' to 3' direction, and several DNA polymerases help with this process. In nuclear DNA replication, DNA polymerase delta and DNA polymerase epsilon have proofreading ability. After a new base is added, these polymerases...

replication in prokaryotes

How Prokaryotic DNA Copies Itself

Prokaryotic DNA copies itself through a set of coordinated steps called initiation, elongation, and termination. In bacteria, replication starts when initiator proteins bind to a single origin of replication, or ori, on the circular chromosome. The DNA is then copied in both directions until two DNA molecules are made. Several proteins help open and stabilize the DNA during replication. Topoisomerase cuts one side of the double-stranded phosphate-sugar backbone so the helix can unwind faster.

Eukaryotic DNA replication copies the genome before cell division. It happens in a tightly regulated way so each daughter cell gets a complete set of chromosomes in the nucleus. The process has three stages: initiation, elongation, and termination. Eukaryotic cells use many proteins to manage replication because their chromosomes are linear and their genomes are larger than those of prokaryotes. Replication begins at multiple origins of replication along each chromosome. Initiator proteins...

telomeres and telomerase

Telomeres and Telomerase in DNA Replication

Telomeres and telomerase help protect chromosomes during DNA replication. Telomeres are repeated DNA sequences at chromosome ends, and telomerase is the enzyme that can extend them. Together, they help keep important genetic information from being lost when cells divide. Each time a chromosome is copied, the very end of the DNA strand can be difficult to replicate fully. Telomeres act like a buffer zone at the tips of chromosomes. Telomerase adds new repeats to these ends, which helps maintain...

overview of dna repair

DNA Repair and Genetic Recombination

DNA repair and genetic recombination help cells respond to damage in DNA. DNA can be harmed by normal cell activity or by outside factors. When damage is not fixed, it can affect how genetic information is copied and used. Cells use repair pathways to detect and correct many kinds of DNA damage. Some repair steps remove damaged bases or replace missing pieces of DNA. Other pathways help keep the DNA sequence stable after damage has occurred. Genetic recombination is also part of this process.

base excision repair

Base Excision Repair Pathway

Base excision repair is a DNA repair pathway that fixes small base damage. It helps cells correct changes that can appear in DNA before they cause larger problems. In this pathway, a damaged base is removed first. The cell then processes the site and replaces the missing part with the correct DNA building block. This repair step helps keep genetic information accurate. Base excision repair is one of the main ways cells handle everyday DNA damage. It is an important part of maintaining DNA...

nucleotide excision repair

UV Damage and DNA Repair by NER

UV damage can bend DNA and block replication or transcription. Cells often face mutagens, which are outside factors that damage DNA and can create mutations. If these changes are not repaired, they can lead to disease or cancer, depending on which DNA sequences are affected. Nucleotide excision repair, or NER, is the pathway that helps cells find and remove damaged DNA. In prokaryotes, three proteins carry out this work: UvrA, UvrB, and UvrC. UvrA and UvrB move along the DNA together and look...

mismatch repair

DNA Mismatch Repair and Cancer Risk

DNA mismatch repair fixes copying errors that happen during DNA replication. It helps cells find the wrong nucleotide, remove it, and replace it with the correct one before the cell divides. Human cells carry more than 3 billion base pairs of DNA, so replication must be very accurate. Even with DNA polymerase proofreading, a copying error can still occur about once every 1 million base pairs. One common error is a mismatch, such as A paired with G or T paired with C. The Mutator protein family...

dna damage can stall the cell cycle

DNA Repair Checkpoints in the Cell Cycle

DNA repair checkpoints help cells pause the cell cycle after DNA damage. This pause gives the cell time to check for breaks and repair them before division continues. Cells must do this at critical stages of the cycle. The amount of DNA in the cell depends on when the pause happens. If the cycle stops before DNA replication, the cells will contain twice the normal amount of DNA. If cells stop after DNA replication but before mitosis, they will contain four times the normal amount. Cells use...

fixing double-strand breaks

Repairing DNA Double-Strand Breaks

Repairing DNA double-strand breaks is an important part of DNA maintenance. A double-strand break happens when both strands of the DNA molecule are cut. Cells must fix this damage to keep genetic information stable. The repair process can happen by more than one pathway. Some breaks are repaired by direct joining of the broken ends. Other breaks are repaired by using a matching DNA sequence as a template. These pathways help cells respond to damage in different ways. This topic is closely...

homologous recombination

Homologous Recombination in DNA Repair

Homologous recombination is a DNA repair process that uses a matching DNA sequence as a template. It helps cells fix breaks in DNA and keep genetic information accurate. The process begins when a broken DNA strand finds a similar, or homologous, piece of DNA. That matching sequence guides repair and allows the damaged DNA to be restored. Because the repair uses a copied sequence, the final DNA can closely match the original information. Homologous recombination is also important in genetic...

gene conversion

Gene Conversion During DNA Repair

Gene conversion is a DNA repair event linked to genetic recombination. It can change the sequence of one DNA region by using a related DNA strand as a template. This process is important for understanding how cells repair damage and reshuffle genetic information. During recombination, gene conversion can copy information from one DNA molecule to another. The result is not a simple swap of DNA segments. Instead, one sequence is corrected or replaced while the related partner sequence remains...

restarting stalled replication forks

Restarting DNA Replication After Stalls

DNA replication can stop before it is finished when the fork stalls. A stalled replication fork is a point where the DNA-copying machinery slows down or pauses during chromosome duplication. Cells can restart these forks to keep copying DNA. This process helps the replication machinery move forward again after the pause. It is an important part of maintaining normal DNA replication when problems arise during copying. The term stalled replication fork describes the stopped or delayed state of...

key terms and concepts

Learn how eukaryotic DNA replication works, including origins, helicase, leading and lagging strands, polymerases, and telomeres in high school biology.

Eukaryotic DNA Replication Steps | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Pennsylvania State Academic Standards

Life Science

Inheritance and Variation of Traits

3.1.9-12.Q

Louisiana Student Standards for Science

High School

Life Sciences

Heredity: Inheritance And Variation Of Traits

HS-LS3-3

Alabama Course of Study Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.B.1.3.a

Florida Department of Education

SC.912.L.16

SC.912.L.16.3

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Proofreading

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Restarting Stalled Replication Forks

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Obtain and communicate information that summarizes the impact of biotechnology applications on the individual, society, and the environment, including agriculture and medicine.

LS.Bio.8.2

Understand genetic mechanisms for variation.

Eukaryotic DNA Replication Steps

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