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

- [Istruttore] Nei procarioti
la replicazione del DNA inizia

quando le proteine dell&#x27;iniziatore
si legano all&#x27;origine

della replicazione. Una piccola
regione di DNA che contiene

una sequenza specifica di
basi e creano un complesso.

Questo complesso aiuta a
separare inizialmente il DNA.

Quindi l&#x27;enzima elicasi
del DNA si lega ad esso

e continua a scaricare il DNA rompendo

i legami di idrogeno tra
i filamenti complementari.

Le aree appena aperte sono stabilizzate

da proteine che legano il
DNA al filamento singolo.

Ognuno pu&#xF2; ora servire
come modello per la sintesi

di un nuovo filone di DNA.

Lo svolgimento e la sintesi
procede in entrambe le direzioni

dall&#x27;origine creando due fork di replica.

Di fronte alle forcelle gli
enzimi topoisomerasi si legano

al DNA e riducono lo sforzo torsionale

mentre la molecola si svolge.

Una volta separati i fili,

un altro enzima primasi
sintetizza un RNA primer.

Un breve tratto di RNA
complementare alla sequenza del DNA.

Il primer fornisce un posto
per l&#x27;enzima polimerasi del DNA

per aggiungere nucleotidi
complementari alla

sequenza del DNA, creando
un nuovo filamento di DNA

in un processo chiamato allungamento.

La polimerasi DNA sintetizza
il DNA nei cinque primi

a tre prime direzione di una molecola.

Quindi per la sintesi di questo filamento,

il filamento conduttore
procede ininterrottamente.

L&#x27;altro filamento, il filamento lagging

ha l&#x27;orientamento opposto.

Di conseguenza, il DNA viene sintetizzato

in brevi pezzi chiamati
frammenti di Okazaki,

prolungati da RNA primer aggiuntivi.

Andando indietro dalla
direzione generale del movimento

della forcella di replicazione.

Gli RNA primer vengono quindi
eliminati da enzimi come RNAse

sostituiti con DNA e frammenti di DNA

sono uniti dall&#x27;enzima ligasi del DNA,

creando un filamento continuo.

La replicazione del DNA
procede intorno all&#x27;intera

molecola risultante in due
molecole di DNA circolari.

Questo &#xE8; considerato un
processo semiconservativo

perch&#xE9; ogni molecola contiene

un vecchio filamento e uno nuovo.

replicazione nei procarioti

<h4>Panoramica</h4>

La replicazione del DNA ha tre passaggi principali: avvio, allungamento e terminazione. La replicazione nei procarioti inizia quando le proteine iniziatore si legano alla singola origine della replicazione (ori) sul cromosoma circolare della cellula. La replicazione procede quindi intorno all&#x27;intero cerchio del cromosoma in ogni direzione da due forche di replicazione, con conseguente due molecole di DNA.

<h4>Molte proteine lavorano insieme per replicare il cromosoma</h4>

La replicazione &#xE8; coordinata ed eseguita da una serie di proteine specializzate. La topoisomerase rompe un lato della spina dorsale (o colonna portante) del fosfato-zucchero del DNA a doppio filamento, permettendo all&#x27;elica del DNA di distrarsi pi&#xF9; rapidamente, mentre l&#x27;elicasi rompe i legami tra le coppie di basi alla forcella, separando il DNA in due fili modello. Le proteine che legano molecole di DNA a filamento singolo stabilizzano i filamenti mentre la forcella di replicazione viaggia lungo il cromosoma. Il DNA pu&#xF2; essere sintetizzato solo nella direzione da 5&#x27; a 3&#x27;, quindi un filamento del modello, il filamento principale, &#xE8; allungato continuamente, mentre l&#x27;altro filamento, il filamento in ritardo, viene sintetizzato in pezzi pi&#xF9; brevi di 1000-2000 coppie di basi chiamate frammenti di Okazaki.

<h4>Polimerasi multiple prendono parte nell&#x27;allungamento</h4>

Gran parte della ricerca per comprendere la replicazione del DNA procariotico &#xE8; stata eseguita nel batterio Escherichia coli, un organismo modello comunemente usato. E. coli ha 5 polimerasi del DNA: Pol I, II, III, IV e V. Pol III sono responsabili della maggior parte della replicazione del DNA. Pu&#xF2; polimerizzare circa 1.000 coppie di basi al secondo. Questo ritmo sorprendente permette ai macchinari presenti presso i due forcella di replicazione di duplicare il cromosoma E. coli , 4,6 milioni di coppie di basi, in circa 40 minuti. La polimerasi del DNA I &#xE8; anche ben caratterizzata; il suo ruolo principale &#xE8; quello di rimuovere i primer dell&#x27;RNA dall&#x27;inizio dei frammenti di Okazaki sul filamento in ritardo.

<h4>Quando la divisione supera la duplicazione</h4>

In condizioni di crescita favorevoli, E. coli si divider&#xE0; ogni 20 minuti, circa la met&#xE0; del tempo necessario per replicare il genoma. Com&#x27;&#xE8; possibile quando entrambe le cellule figlie devono avere il proprio DNA? Gli scienziati hanno scoperto che i batteri possono iniziare un altro ciclo di replicazione del DNA dall&#x27;origine della replicazione prima che il primo round sia completo; ci&#xF2; significa che le cellule figlie ricevono un cromosoma che &#xE8; gi&#xE0; in fase di copia e sono pronte a dividersi di nuovo molto rapidamente.

Replicazione nei procarioti

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

Struttura e funzione del DNA

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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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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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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

Nucleic Acids

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The DNA Helix

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DNA Base Pairing

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The Central Dogma

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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

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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
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RNA Stability

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pre-mRNA Processing

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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 Folding

Protein Families

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conservation-of-protein-domains-over-different-proteins

Conservation of Protein Domains Over Different Proteins

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Globular and Fibrous Proteins

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Intrinsically Disordered Proteins

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Protein Complex Assembly

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Conjugated Proteins

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Allosteric Proteins-ATCase

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Amyloid Fibrils

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Cooperative Allosteric Transitions

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Antibody Structure

Phosphorylation

Ligand Binding Sites

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Protein Kinases and Phosphatases

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Protein-protein Interfaces

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GTPases and their Regulation

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Conserved Binding Sites

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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

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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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