Name: how prokaryotic dna is copied
Uploaded: 2026-08-26T08:20:08.548Z
Duration: 2 min 57 s
Channel: JoVE

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From Molecules to Organisms: Structures and Processes

BIO1.LS1.3

Replication in Prokaryotes

- [Instructeur] Chez les procaryotes,la r&#xE9;plication de l&#x27;ADN commencelorsque les prot&#xE9;ines initiatrices se lient&#xE0; l&#x27;origine de la r&#xE9;plication. 
Une petite r&#xE9;gion d&#x27;ADN contenant une s&#xE9;quence sp&#xE9;cifiquede base cr&#xE9;ant un complexe. 
Ce complexe aide &#xE0; s&#xE9;parer initialement l&#x27;ADN. 
Ensuite, l&#x27;enzyme ADN h&#xE9;licase, se lie &#xE0; elleet continue &#xE0; d&#xE9;rouler l&#x27;ADN en cassantles liaisons hydrog&#xE8;ne entre les brins compl&#xE9;mentaires. 
Les zones nouvellement ouvertes sont stabilis&#xE9;espar des prot&#xE9;ines de liaison &#xE0; l&#x27;ADN brin unique. 
Chacun peut maintenant servir de matrice pour la synth&#xE8;sed&#x27;un nouveau brin d&#x27;ADN. 
Le d&#xE9;roulement et la synth&#xE8;se continuent dans les deux sens&#xE0; partir de l&#x27;origine en cr&#xE9;antdeux fourches de r&#xE9;plication. 
Face &#xE0; la fourche, les enzymes de la topoisom&#xE9;rase se lient&#xE0; l&#x27;ADN et r&#xE9;duisent les tensions dues &#xE0; la torsionlorsque la mol&#xE9;cule se d&#xE9;roule. 
Une fois que les brins sont s&#xE9;par&#xE9;s,une autre enzyme, la primase, synth&#xE9;tise une amorce d&#x27;ARN. 
Un court segment d&#x27;ARN compl&#xE9;mentaire &#xE0; la s&#xE9;quence d&#x27;ADN. 
L&#x27;amorce fournie &#xE0; l&#x27;enzyme ADN polym&#xE9;rase une possibilit&#xE9;d&#x27;ajouter des nucl&#xE9;otides compl&#xE9;mentaires &#xE0;la s&#xE9;quence d&#x27;ADN, cr&#xE9;ant ainsi un nouveau brin d&#x27;ADNselon un processus appel&#xE9; &#xE9;longation. 
L&#x27;ADN polym&#xE9;rase synth&#xE9;tise l&#x27;ADN dans les cinqdirections principales d&#x27;une mol&#xE9;cule. 
La synth&#xE8;se de ce brin,le brin principal, se poursuit donc continuellement. 
L&#x27;autre brin, le brin calorifuge,a une orientation oppos&#xE9;e. 
Par cons&#xE9;quent, l&#x27;ADN est synth&#xE9;tis&#xE9;en petits morceaux appel&#xE9;s fragments d&#x27;Okazaki,allong&#xE9;s &#xE0; partir d&#x27;amorces d&#x27;ARN suppl&#xE9;mentaires. 
En arri&#xE8;re par rapport &#xE0; la direction g&#xE9;n&#xE9;rale du mouvementde la fourche de r&#xE9;plication. 
Les amorces d&#x27;ARN sont ensuite excis&#xE9;espar des enzymes comme la RNAseremplac&#xE9;e par de l&#x27;ADN et les fragments d&#x27;ADNsont reli&#xE9;s entre eux par l&#x27;enzyme ADN ligase,cr&#xE9;ant un brin continu. 
La r&#xE9;plication de l&#x27;ADN se d&#xE9;roule autourde la mol&#xE9;cule enti&#xE8;repour donner deux mol&#xE9;cules d&#x27;ADN circulaires. 
Ceci est consid&#xE9;r&#xE9; comme un processus semi-conservateurcar chaque mol&#xE9;cule contientun ancien brin et un nouveau brin.

réplication chez les procaryotes

<h4>Aper&#xE7;u</h4>
 
 La r&#xE9;plication de l&#x2019;ADN comporte trois &#xE9;tapes principales : l&#x2019;initiation, l&#x2019;&#xE9;longation et la terminaison. La r&#xE9;plication des procaryotes commence lorsque les prot&#xE9;ines initiatrice se lient &#xE0; l&#x2019;origine unique de la r&#xE9;plication (ori) sur le chromosome circulaire de la cellule. La r&#xE9;plication se poursuit ensuite autour du cercle entier du chromosome dans chaque direction &#xE0; partir de deux fourches de r&#xE9;plication, donnant lieu &#xE0; deux mol&#xE9;cules d&#x2019;ADN.
 
 <h4>De nombreuses prot&#xE9;ines fonctionnent ensemble pour r&#xE9;pliquer le chromosome</h4>
 
 La r&#xE9;plication est coordonn&#xE9;e et r&#xE9;alis&#xE9;e par un groupe de prot&#xE9;ines sp&#xE9;cialis&#xE9;es. La topoisom&#xE9;rase brise un c&#xF4;t&#xE9; du squelette phosphate-sucre de l&#x27;ADN double brin, permettant &#xE0; l&#x2019;h&#xE9;lice d&#x2019;ADN de se d&#xE9;rouler plus rapidement, tandis que l&#x2019;h&#xE9;licase rompt les liaisons entre les paires de bases au niveau de la fourche, s&#xE9;parant l&#x2019;ADN en deux brins matrices. Les prot&#xE9;ines qui lient les mol&#xE9;cules d&#x2019;ADN &#xE0; brin unique stabilisent les brins au fur et &#xE0; mesure que la fourche de r&#xE9;plication se d&#xE9;place le long du chromosome. L&#x2019;ADN ne peut &#xEA;tre synth&#xE9;tis&#xE9; que dans la direction de 5&#x2019; &#xE0; 3&#x2019;, de sorte que l&#x2019;&#xE9;longation d&#x2019;un brin de la matrice &#x2014; le brin en avance &#x2014; se fait en continu, tandis que l&#x2019;autre brin &#x2014; le brin en retard &#x2014; est synth&#xE9;tis&#xE9; en morceaux plus courts de 1000-2000 paires de bases appel&#xE9;s fragments d&#x2019;Okazaki.
 
 <h4>Plusieurs polym&#xE9;rases participent &#xE0; l&#x2019;&#xE9;longation</h4>
 
 Une grande partie de la recherche pour comprendre la r&#xE9;plication de l&#x2019;ADN procaryote a &#xE9;t&#xE9; effectu&#xE9;e dans la bact&#xE9;rie Escherichia coli, un organisme mod&#xE8;le couramment utilis&#xE9;. E. coli a 5 ADN polym&#xE9;rases : Pol I, II, III, IV, et V. Pol III est responsable de la majorit&#xE9; de la r&#xE9;plication d&#x2019;ADN. Elle peut polym&#xE9;riser environ 1 000 paires de bases par seconde. Ce rythme &#xE9;tonnant permet aux machineries pr&#xE9;sentes dans les deux fourches de r&#xE9;plication de dupliquer le chromosome de E. coli &#x2014; 4,6 millions de paires de bases &#x2014; en environ 40 minutes. L&#x2019;ADN polym&#xE9;rase I est &#xE9;galement bien caract&#xE9;ris&#xE9;e ; son r&#xF4;le principal est d&#x2019;enlever les amorces d&#x2019;ARN au d&#xE9;but des fragments d&#x2019;Okazaki sur le brin en retard.
 
 <h4>Quand la division d&#xE9;passe la duplication</h4>
 
 Dans des conditions de croissance favorables, E. coli se divise toutes les 20 minutes, soit environ la moiti&#xE9; du temps qu&#x2019;il faut pour r&#xE9;pliquer le g&#xE9;nome. Comment est-ce possible lorsque les deux cellules filles doivent avoir leur propre ADN ? Les scientifiques ont constat&#xE9; que les bact&#xE9;ries peuvent commencer une autre s&#xE9;rie de r&#xE9;plication de l&#x2019;ADN &#xE0; partir de l&#x2019;origine de la r&#xE9;plication avant que le premier cycle soit termin&#xE9; ; cela signifie que les cellules filles re&#xE7;oivent un chromosome qui est d&#xE9;j&#xE0; en train d&#x2019;&#xEA;tre copi&#xE9; et sont pr&#xEA;tes &#xE0; se diviser &#xE0; nouveau tr&#xE8;s rapidement.

Réplication chez les procaryotes

Overview

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

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DNA Structure and Function

Structure et fonction de l'ADN

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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 double-stranded DNA phosphate-sugar backbone so the helix can unwind more quickly. Helicase breaks the bonds between base pairs at the fork and separates the DNA into two template strands. Single-strand DNA-binding proteins then stabilize the exposed strands as the fork moves along the chromosome.

DNA synthesis can only happen in the 5’ to 3’ direction. Because of this, the leading strand is made continuously, while the lagging strand is made in short sections called Okazaki fragments. These fragments are about 1000 to 2000 base pairs long.

Research on this process has often used Escherichia coli, a common model organism. E. coli has five DNA polymerases: Pol I, II, III, IV, and V. Pol III does most of the replication and can add about 1,000 base pairs per second. That speed helps the two replication forks copy the 4.6 million base pair chromosome in about 40 minutes. Pol I is also well studied, and its main role is to remove the RNA primers at the start of Okazaki fragments on the lagging strand.

Under favorable growth conditions, E. coli can divide every 20 minutes, which is faster than the time needed to copy the genome once. Scientists found that the cell can start another round of replication before the first one is finished. As a result, daughter cells receive a chromosome that is already being copied and can divide again very quickly.

How Prokaryotic DNA Is Copied

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

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organization of genes

Genes, Introns, and Regulatory DNA

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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

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...

replication in eukaryotes

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...

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 prokaryotic DNA is copied, from origin binding and replication forks to leading and lagging strands, polymerases, and fast E. coli division.

How Prokaryotic DNA Is Copied | JoVE K12

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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.
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Evaluate comparative models of various cell types with a focus on organic molecules that make up cellular structures.
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BIO1.LS1.2

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DNA Packaging

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Organization of Genes

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Karyotyping

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Replication in Eukaryotes

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Mutations

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Transcription

Overview
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Translation

Lesson: Translation
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RNA Structure

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Types of RNA

Overview
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MicroRNAs

siRNA - Small Interfering RNAs

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piRNA - Piwi-interacting RNAs

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Allosteric Proteins-ATCase

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Antibody Structure

Phosphorylation

Ligand Binding Sites

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Protein Kinases and Phosphatases

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Covalently Linked Protein Regulators

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Protein Complexes with Interchangeable Parts

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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).

How Prokaryotic DNA Is Copied

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