Name: eukaryotic dna copying and telomeres
Uploaded: 2026-08-26T08:19:39.013Z
Duration: 2 min 37 s
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From Molecules to Organisms: Structures and Processes

BIO1.LS1.3

Replication in Eukaryotes

Most prokaryotic factors used during replication have equivalents that play similar roles in eukaryotic DNA replication.This process starts at an origin of replication, where a recognition complex binds.Helicase then moves to the site and separates the DNA strands, creating a replication bubble with two forks.Primase then synthesizes short RNA primers. As helicase moves forward, DNA polymerase extends the primers by adding complementary DNA nucleotides in the 5-prime-to-3-prime direction.As in prokaryotes, the newly formed leading strand grows continuously, following the replication fork.The lagging strand forms short Okazaki fragments that grow in the opposite direction of the replication fork. Because of the structure of the replication bubble, the DNA template that supports leading-strand synthesis on one side supports lagging-strand synthesis on the other side.Several origins of replication are present on a linear eukaryotic chromosome, and replication ends when neighboring replication bubbles merge. RNA primers are then removed by RNase. The DNA polymerase fills the gap with DNA. DNA ligase then joins the remaining DNA segments.When the final primer is removed from the lagging strand, a gap remains, leaving a short stretch of the DNA template uncopied. To solve this problem, an enzyme called telomerase binds to the overhanging region and extends it with a non-coding DNA sequence.Then, primase adds a short primer sequence, and DNA polymerase extends the region, forming a telomere that protects against the loss of coding DNA on the lagging strand during repeated rounds of replication.So, eukaryotic DNA replication produces two DNA molecules, each made up of one parental strand and one newly synthesized strand. It uses multiple origins of replication and telomeres to duplicate the entire chromosome.

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 fill 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 OriginEukaryotic 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. Replication occurs simultaneously at multiple origins of replication along each chromosome. Initiator proteins recognize and bind to the origin, recruiting helicase 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&#x2019; to 3&#x2019; 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 100-200 base pairs in length, called Okazaki fragments. Once the bulk of replication is complete, RNase enzymes remove the RNA primers and DNA ligase joins any gaps in the new strand.Dividing the Work of Replication among PolymerasesThe 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 &#x3B1;, which also functions as a primase at the replication fork, and Pol &#x3B4; and &#x3B5;, 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 DegradationBecause 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&#x2019; overhang at each end of the chromosome interacts with specialized proteins, which stabilizes 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 they 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.

Overview

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

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eukaryotic dna copying and telomeres

Eukaryotic DNA copying is tightly regulated and must duplicate many linear chromosomes before cell division. The process is highly conserved and uses many proteins with specialized roles. It moves through initiation, elongation, and termination, and it ends with two complete sets of chromosomes in the nucleus.

Eukaryotic replication shares basic steps with prokaryotic DNA replication, but the larger genome and linear chromosomes require more proteins. Replication begins at multiple origins of replication along each chromosome. Initiator proteins bind the origin and recruit helicase, which unwinds the DNA double helix. Two replication forks form at each origin. Primase then adds short RNA primers to the single strands, and these primers let DNA polymerase bind and start copying the DNA.

DNA synthesis can only proceed in the 5′ to 3′ direction, so the two strands are copied in different ways at each replication fork. The leading strand is made continuously. The lagging strand is made in short stretches of 100 to 200 base pairs called Okazaki fragments. After most replication is finished, RNase enzymes remove the RNA primers, and DNA ligase seals the remaining gaps in the new strand.

Eukaryotic cells use several DNA polymerases to divide the work of replication. Polymerase families are grouped by similarities in protein structure and amino acid sequence. Early families were called A, B, C, and X, and Y and D were identified later. In eukaryotes, family B polymerases include Pol alpha, which also works as a primase at the replication fork, and Pol delta and epsilon, which do most of the DNA copying on the leading and lagging strands. Other polymerases help repair DNA damage, copy mitochondrial and plastid DNA, and fill gaps left on the lagging strand after RNA primers are removed.

Because eukaryotic chromosomes are linear, their ends need special protection. These ends contain telomeres, which are long 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. Still, the lagging strand cannot fully copy the telomeric DNA during every cell division, so telomeres become shorter over many cell cycles and 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 cell division before shortening occurs.

Eukaryotic DNA Copying and Telomeres

the dna helix

How DNA Stores Genetic Information

DNA stores genetic information that is passed from one generation to the next in organisms and most viruses. It is built from two strands of nucleotides that twist together into a double helix. The story of how scientists uncovered this structure developed step by step over nearly a century. Each DNA strand is made of nucleotides. A nucleotide contains the sugar deoxyribose, a phosphate group, and one of four nitrogen bases: adenine (A), guanine (G), cytosine (C), or thymine (T). Adenine and...

dna packaging

Chromatin and Histones in DNA Packing

Eukaryotic cells must pack long DNA molecules into the nucleus, and chromatin makes that possible. DNA wraps around proteins called histones to form nucleosomes, which are the main unit of DNA packaging. Nucleosomes then coil into compact chromatin fibers. The amount of DNA in a cell is much larger than it first seems. A single human skin cell has about 3 billion base pairs of DNA, and if that DNA were stretched out in a line, it would be about 2 meters long. With about 50 trillion cells in...

organization of genes

Genes, Introns, and Regulatory DNA

Eukaryotic genes are arranged within DNA along with non-coding regions that help control gene activity. A DNA strand includes genes and intergenic regions, which are the stretches between genes. These regions do not code for proteins, but they can contain important regulatory elements such as promoters, enhancers, and silencers. A gene itself is not a single continuous coding block. It usually contains protein-coding exons and non-coding introns. After DNA is transcribed into pre-mRNA in the...

karyotyping

Chromosome Stains for Detecting Disorders

Chromosome staining helps scientists find genetic disorders by showing the number and physical features of chromosomes. These features appear after DNA condenses into chromosomes during mitosis. Cytogeneticists then stop mitosis and stain the chromosomes to study their banding pattern. The pattern reveals details such as chromosome number, shape, and type. A chromosome description like this is called a karyotype. To create one, scientists take an image of the stained chromosomes and identify...

replication in prokaryotes

How Prokaryotic DNA Is Copied

Prokaryotic DNA is copied through a coordinated process with three main stages: initiation, elongation, and termination. It begins when initiator proteins bind to the single origin of replication, or ori, on the cell’s circular chromosome. The DNA then copies around the circle in both directions, starting from two replication forks, and this produces two DNA molecules. Several proteins work together to open and protect the DNA during replication. Topoisomerase cuts one side of the...

Eukaryotic DNA copying is tightly regulated and must duplicate many linear chromosomes before cell division. The process is highly conserved and uses many proteins with specialized roles. It moves through initiation, elongation, and termination, and it ends with two complete sets of chromosomes in the nucleus. Eukaryotic replication shares basic steps with prokaryotic DNA replication, but the larger genome and linear chromosomes require more proteins. Replication begins at multiple origins of...

proofreading

DNA Polymerase Fixes Replication Errors

DNA polymerase helps copy DNA and fix mistakes during replication. It adds nucleotides in a sequence that matches the template DNA strand. The enzyme also has a higher affinity for the correct base, which helps keep DNA replication accurate. As new genomic DNA is made, it is synthesized in the 5’ to 3’ direction. In many cells, DNA polymerases have different jobs in this process. DNA polymerase delta and DNA polymerase epsilon can proofread when nuclear DNA is being copied. These polymerases...

mismatch repair

DNA Mismatch Repair in Replication

DNA mismatch repair fixes copying errors that happen during DNA replication. When DNA polymerase makes a mistake, the cell can detect a wrong base pair, such as A with G or T with C, and replace it with the correct nucleotide. This repair system works in both prokaryotes and eukaryotes and depends on several proteins. The Mutator protein family plays a central role in this process. In bacteria such as Escherichia coli, MutS first binds the mismatch. MutL then helps identify which strand is the...

nucleotide excision repair

DNA Damage Repair by Excision

DNA damage repair by excision protects cells from mutagens that can change DNA. Exposure to environmental mutagens can create bulky lesions that bend the double helix or block transcription. If these changes are not repaired, they can lead to mutations and may contribute to cancer or disease, depending on which DNA sequences are affected. Nucleotide excision repair, or NER, is the process that detects and removes this kind of damage. Specialized proteins scan the DNA for a damaged region, then...

mutations

DNA Changes From Point Mutations to UV Damage

Mutations are changes in the DNA sequence. They can happen by chance during DNA copying, or they can be caused by environmental factors such as radiation and chemicals. Scientists also describe mutations by how much DNA they affect, how they change a protein, and whether they happen in body cells or germline cells. Some mutations affect only one nucleotide, which is a point mutation. When a point mutation falls inside a gene, the outcome depends on how the amino acid sequence changes. A silent...

transcription

Transcription and Gene Control

Transcription and gene control explain how cells make RNA from DNA and decide which genes are active. RNA polymerase copies a DNA sequence into RNA, and this is the first step in making a protein from a gene. Many other proteins and control sequences help make messenger RNA, or mRNA, correctly. In eukaryotes, the DNA is first copied into a primary RNA, also called pre-mRNA. This RNA can then be processed into mature mRNA, which serves as the template for protein synthesis. In prokaryotes such...

translation

Protein Synthesis and mRNA Decoding

Protein synthesis begins when ribosomes decode messenger RNA (mRNA) and build a chain of amino acids. This final step of gene expression is called translation. The finished chain is a polypeptide, which can later become a functional protein. Proteins are often called the building blocks of life because they make up much of the body, from muscle fibers to hairs and immune system parts. The instructions for each protein are encoded in genes found in the DNA of every cell. In biology, the central...

bacterial transformation

Griffith’s Mouse Experiment and DNA

Bacterial transformation explains how DNA can move into bacteria and change their traits. Frederick Griffith first noticed this in 1928 while studying pneumonia-causing Streptococcus pneumoniae in mice. He compared one pathogenic strain with one non-pathogenic strain and found that only the pathogenic strain killed the host mice. Griffith made an unexpected discovery when he killed the pathogenic bacteria and mixed their remains with live, non-pathogenic bacteria. The mixture killed the mice,...

key terms and concepts

Explore how eukaryotic cells copy DNA using origins, helicase, primase, polymerases, and telomeres, and learn why chromosome ends shorten over time.

Eukaryotic DNA Copying and Telomeres | JoVE K12

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Characteristics of Life

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Levels of Organization

Biological organization is the classification of biological structures, ranging from atoms at the bottom of the hierarchy to the Earth&#x27;s biosphere. ...

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The Tree of Life - Bacteria, Archaea, and Eukaryotes

Prokaryotic Cells

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Introduction to Virus

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Size and Structure of Viral Genomes

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Compare and contrast existing models, identify patterns, and use structural and functional evidence to analyze the characteristics of life. Engage in argument about the designation of viruses as non-living based on these characteristics.
EXPLANATION: Students begin to develop patterns of living and non-living organisms in kindergarten and build on detailed characteristics of different classifications of living organisms throughout elementary and middle school. Biology 1 discussions introduce viral particles and viral cycles, building on student understanding of living organisms to engage in an argument regarding the classification of a viral particle as either living or non-living.

BIO1.LS1.1

What are Cells?

Cells are the smallest and basic units of life, whether it is a single cell that forms the entire organism, e.g., in a bacterium, or trillions of them, ...

Eukaryotic Compartmentalization

One of the distinguishing features of eukaryotic cells is that they contain membrane-bound organelles, such as the nucleus and mitochondria, that carry ...

Eukaryotic Evolution

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Animal and Plant Cell Structure

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Evaluate comparative models of various cell types with a focus on organic molecules that make up cellular structures.
EXPLANATION: Students explicitly discuss the structure and function of major cellular organelles in seventh grade. Building on this understanding, Biology I students should shift their focus to the different types of cells found in organisms and how the role of each cell type relates to its composition and the prevalence of different organelles within that cell. An example might include the absence (or enucleation) of the nucleus in red blood cells in mammals providing for increased levels of oxygen transport in organisms or the lack of centrioles in most neurons. Varying cell types can include both prokaryotic and eukaryotic cell types.

BIO1.LS1.2

Nucleic Acids

Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and carry instructions for its ...

The DNA Helix

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DNA Base Pairing

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The Central Dogma

The central dogma explains the flow of genetic information from DNA nucleotides to the amino acid sequence of proteins.
RNA is the Missing Link Between ...

DNA Packaging

Overview

Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

Organization of Genes

Overview

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

Karyotyping

Describing the number and physical features of chromosomes can reveal abnormalities that underlie genetic diseases. This description is facilitated by ...

Replication in Prokaryotes

Overview

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to ...

Mutations

Overview

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. ...

Transcription

Overview
Transcription is the process of synthesizing RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene ...

Translation

Lesson: Translation
Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following ...

RNA Structure

Overview
The basic structure of RNA consists of a five-carbon sugar and one of four nitrogenous bases. Although most RNA is single-stranded, it can form ...

RNA Stability

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations ...

pre-mRNA Processing

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or ...

Types of RNA

Overview
Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs ...

MicroRNAs

siRNA - Small Interfering RNAs

Small interfering RNAs, or siRNAs, are short regulatory RNA molecules that can silence genes post-transcriptionally, as well as the transcriptional ...

piRNA - Piwi-interacting RNAs

PIWI-interacting RNAs, or piRNAs, are the most abundant short non-coding RNAs. More than 20,000 genes have been found in humans that code for piRNAs while ...

CRISPR and crRNAs

Bacteria and archaea are susceptible to viral infections just like eukaryotes; therefore, they have developed a unique adaptive immune system to protect ...

lncRNA - Long Non-coding RNAs

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Protein Organization

Protein Folding

Protein Families

Protein families are groups of homologous proteins; that is, they have similarities in amino acid sequences and three-dimensional structures. Protein ...

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Conservation of Protein Domains Over Different Proteins

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Globular and Fibrous Proteins

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Globular ...

Intrinsically Disordered Proteins

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Protein Complex Assembly

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Conjugated Proteins

Simple proteins and protein complexes contain only amino acids. In contrast, many other proteins, called conjugated proteins, covalently bond with ...

Allosteric Proteins-ATCase

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Amyloid Fibrils

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Cooperative Allosteric Transitions

Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand ...

Antibody Structure

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Ligand Binding Sites

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Protein Kinases and Phosphatases

Proteins undergo chemical modifications that trigger changes in the charge, structure, and conformation of the proteins. Phosphorylation, acetylation, ...

Protein-protein Interfaces

Many proteins form complexes to carry out their functions, making protein-protein interactions (PPIs) essential for an organism&#39;s survival. Most PPIs ...

GTPases and their Regulation

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Conserved Binding Sites

Many proteins&#8217; biological role depends on their interactions with their ligands, small molecules that bind to specific locations on the protein ...

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an ...

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The Equilibrium Binding Constant and Binding Strength

The equilibrium binding constant (Kb) quantifies the strength of a protein-ligand interaction. Kb can be calculated as follows when the reaction is at ...

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Protein Complexes with Interchangeable Parts

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Cofactors and Coenzymes

Mechanical Protein Functions

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Structural Protein Function

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Protein Networks

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Integrate evidence to develop a structural model of a DNA molecule. Using the model, develop and communicate an explanation for how DNA serves as a template for self-replication and encodes biological information.
EXPLANATION: Discussions of DNA in earlier grades have been limited to discussions of genes and the role of genes in the appearance and activities of an organism. Biology 1 represents a student's introduction to a molecular model of a DNA as well as the organization of DNA into genes and genes subsequently into chromosomes. Students should address interactions between genes in proteins which regulate both the shape and reproduction of DNA molecules. It is important to note that not all segments of DNA are transcribed for proteins. Portions of DNA are involved in regulating the expression of genes or affect the structure of the chromosomes (replication origin, centromeres, and telomeres).

Eukaryotic DNA Copying and Telomeres

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