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

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Replication in Prokaryotes

Bei Prokaryoten beginnt die DNA-Replikation, wenn sich Initiatorproteine am Replikationsursprung binden.
 Eine kleine Region der DNA, die eine spezifische Sequenz von Basen enth&#xE4;lt, die einen Komplex bilden.
 Dieser Komplex hilft, die DNA zun&#xE4;chst zu trennen.
 Dann bindet sich das DNA-Helikase-Enzym daran und zerlegt die DNA weiter, indem es die Wasserstoffbindungen zwischen den komplement&#xE4;ren Str&#xE4;ngen bricht.
 Die neu er&#xF6;ffneten Bereiche werden durch einzelstr&#xE4;ngige DNA-Bindungsproteine stabilisiert.
 Jeder einzelne kann nun als Vorlage f&#xFC;r die Synthese eines neuen DNA-Strangs dienen.
 Die Abwicklung und Synthese erfolgt in beide Richtungen vom Ursprung aus und erzeugt zwei Replikationsgabeln.
 Vor den Gabeln binden sich die Topoisomerase-Enzyme an die DNA und reduzieren die Torsionsbelastung beim Abbauen des Molek&#xFC;ls.
 Sobald die Str&#xE4;nge getrennt sind, synthetisiert eine andere Enzymprimase einen RNA-Primer.
 Ein kurzer Abschnitt der RNA, komplement&#xE4;r zur DNA-Sequenz.
 Der Primer bietet dem DNA-Polymerase-Enzym einen Platz, um Nukleotide hinzuzuf&#xFC;gen, die komplement&#xE4;r zur DNA-Sequenz sind, wodurch ein neuer DNA-Strang in einem Prozess namens Dehnung entsteht.
 Die DNA-Polymerase synthetisiert DNA in der f&#xFC;nf- bis dreimaligen Hauptrichtung eines Molek&#xFC;ls.
 Die Synthese dieses Strangs, des Leitstrangs, verl&#xE4;uft also kontinuierlich.
 Der andere Strang, der Isolierstrang, hat die entgegengesetzte Ausrichtung.
 Folglich wird die DNA in kurzen St&#xFC;cken, den Okazaki-Fragmenten, synthetisiert, die durch zus&#xE4;tzliche RNA-Primer verl&#xE4;ngert werden.
 R&#xFC;ckw&#xE4;rts von der Gesamtbewegungsrichtung der Replikationsgabel.
 Die RNA-Primer werden dann durch Enzyme wie RNAse, die durch DNA ersetzt werden, exzidiert und die DNA-Fragmente werden durch das Enzym DNA-Ligase zu einem kontinuierlichen Strang verbunden.
 Die DNA-Replikation verl&#xE4;uft um das gesamte Molek&#xFC;l herum, so dass zwei kreisf&#xF6;rmige DNA-Molek&#xFC;le entstehen.
 Dies gilt als semikonservativer Prozess, da jedes Molek&#xFC;l einen alten und einen neuen Strang enth&#xE4;lt.

replikation in prokaryoten

<h4>&#xDC;berblick</h4>
 
 Die DNA-Replikation besteht aus drei Hauptschritten: Initiation, Elongation und Terminierung. Die Replikation in Prokaryoten beginnt, wenn die Initiatorproteine den einzigen Replikationsursprung (ori) auf dem zirkul&#xE4;ren Chromosom der Zelle binden. Die Replikation verl&#xE4;uft dann um den gesamten Kreis des Chromosoms in jeder Richtung von zwei Replikationsgabeln aus. Das resultiert in zwei DNA-Molek&#xFC;len.
 
 <h4>Bei der Replikation eines Chromosoms arbeiten viele Proteine zusammen</h4>
 
 Die Replikation wird von einer Vielzahl spezialisierter Proteine koordiniert und durchgef&#xFC;hrt. Die Topoisomerase &#xF6;ffnet eine Seite des doppelstr&#xE4;ngigen DNA-Phosphat-Zucker-R&#xFC;ckgrats. Dadurch kann sich die DNA-Helix schneller entwickeln, w&#xE4;hrend die Helikase die Bindungen zwischen den Basenpaaren an der Gabelung &#xF6;ffnet und die DNA in zwei Matrizenstr&#xE4;nge trennt. Proteine, die an einzelstr&#xE4;ngige DNA-Molek&#xFC;le binden, stabilisieren die Str&#xE4;nge, w&#xE4;hrend die Replikationsgabel entlang des Chromosoms wandert. DNA kann nur in Richtung des 5- und 3-Endes synthetisiert werden, so dass ein Strang der Matrize, der Leitstrang, kontinuierlich verl&#xE4;ngert wird, w&#xE4;hrend der andere Strang, der Folgestrang, in k&#xFC;rzeren St&#xFC;cken von 1000-2000 Basenpaaren, die Okazaki-Fragmente genannt werden, synthetisiert wird.
 
 <h4>Mehrere Polymerasen nehmen an der Elongation teil</h4>
 
 Ein Gro&#xDF;teil der Forschung der prokaryotischen DNA-Replikation wurde in dem Bakterium Escherichia coli, einem h&#xE4;ufig verwendeten Modellorganismus, durchgef&#xFC;hrt. E. coli hat 5 DNA-Polymerasen: Pol I, II, III, IV und V. Pol III ist f&#xFC;r den Gro&#xDF;teil der DNA-Replikation verantwortlich. Es kann etwa 1.000 Basenpaare pro Sekunde polymerisieren. Diese erstaunliche Geschwindigkeit erm&#xF6;glicht es der an den beiden Replikationsgabeln vorhandenen Maschinerie, das E. coli Chromosom in etwa 40 Minuten zu duplizieren. Dabei m&#xFC;ssen &#xFC;ber 4,6 Millionen Basenpaare dupliziert werden. Die DNA-Polymerase I wird mittlerweile auch gut charakterisiert. Ihre Hauptaufgabe besteht darin, die RNA-Primer vom Anfang der Okazaki-Fragmente auf dem Folgestrang zu entfernen.
 
 <h4>Wenn die Zellteilung die Duplikation &#xFC;berholt</h4>
 
 Unter g&#xFC;nstigen Wachstumsbedingungen teilen sich E. coli alle 20 Minuten. Das ist etwa die H&#xE4;lfte der Zeit, welche eine Zelle f&#xFC;r die Replikation des Genoms ben&#xF6;tigt. Wie ist das also m&#xF6;glich, wenn doch beide Tochterzellen ihre eigene DNA haben m&#xFC;ssen? Die Wissenschaftler fanden heraus, dass das Bakterium einen weiteren Zyklus der DNA-Replikation vom Replikationsursprung aus beginnen kann, bevor der erste abgeschlossen ist. Das bedeutet, dass die Tochterzellen ein bereits kopiertes Chromosom erhalten und bereit sind, sich sehr schnell wieder zu teilen.

Replikation in Prokaryoten

Overview

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

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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

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

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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Characteristics of Life

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Levels of Organization

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the-tree-of-life-bacteria-archaea-and-eukaryotes

The Tree of Life - Bacteria, Archaea, and Eukaryotes

Prokaryotic Cells

Prokaryotes are small unicellular organisms that include the domains &#8212; Archaea and Bacteria. Bacteria include many common microorganisms, such as ...

Introduction to Virus

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Size and Structure of Viral Genomes

Viral genomes exhibit remarkable diversity in size, structure, and composition, influencing their replication strategies and interactions with host cells. ...

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

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Eukaryotic Compartmentalization

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Eukaryotic Evolution

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Animal and Plant Cell Structure

Animal and plant cells not only differ in their structure, function, and mode of nutrition but also in how they reproduce, specialize, and organize into ...

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

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most viruses. DNA ...

DNA Base Pairing

Erwin Chargaff&#x2019;s rules on DNA equivalence paved the way for the discovery of base pairing in DNA. Chargaff&#x2019;s rules state that in a ...

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 Eukaryotes

Overview

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

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

In humans, more than 80% of the genome gets transcribed. However, only around 2% of the genome codes for proteins. The remaining part produces non-coding ...

What are Proteins?

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

Protein domains are small structurally independent units that are part of a single amino acid chain.&#160; Although these domains are often structurally ...

Globular and Fibrous Proteins

Many proteins can be classified into two distinct subtypes - globular or fibrous. These two types differ in their shapes and solubilities.
Globular ...

Intrinsically Disordered Proteins

Intrinsically disordered proteins are a group of proteins that do not fold into specific three-dimensional structures. Their structural flexibility allows ...

Protein Complex Assembly

Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types.&#160; Most protein complexes ...

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

Binding sites linkages can regulate a protein&#39;s function.&#160; For example, enzyme activity is often regulated through a feedback mechanism where the ...

Amyloid Fibrils

Amyloid fibrils are aggregates of misfolded proteins.&#160; Under most circumstances, misfolded proteins are either refolded by chaperone proteins or ...

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

Phosphorylation

Ligand Binding Sites

Proteins are dynamic macromolecules that carry out a wide variety of essential processes; however, the activities of most proteins depend on their ...

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

Guanine nucleotide-binding proteins (G-proteins), also known as GTPases, are a superfamily of proteins that regulate many cellular processes, such as cell ...

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

Groups of proteins may form a complex where each protein in this complex has a different role in the overall execution of the complex&#8217;s function. ...

Cofactors and Coenzymes

Mechanical Protein Functions

Proteins perform many mechanical functions in a cell. These proteins can be classified into two general categories- proteins that generate mechanical ...

Allosteric Regulation

Structural Protein Function

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Ligand Binding and Linkage

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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).

How Prokaryotic DNA Is Copied

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