Name: dna replication teams in the replisome
Uploaded: 2020-11-23T11:47:35.000Z
Duration: 3 min 1 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Biology

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

From Molecules to Organisms: Structures and Processes

9-12.B.1.3

The Replisome

La replicazione del DNA viene eseguita da un gruppo multiproteico altamente coordinato noto come definito come macchinario di replicazione del DNA, o il replisoma, che aumenta l'efficienza della duplicazione del DNA. I componenti principali di questo meccanismo sono le elicasi, proteine leganti DNA a singolo filamento, DNA primasi, sliding clamps, un clamp loader, e multiple DNA polimerasi, che sono tutte associate una all'altra vicino alla forcella di replicazione. Le DNA polimerasi replicative hanno una processività di circa 10 nucleotidi, ossia il numero di nucleotidi che si può aggiungere al filamento figlio prima di dissociarsi dal filamento di stampo.Il numero risulta inefficiente per copiare interi genomi in un ragionevole lasso di tempo;problema risolto con l'aiuto di proteine sliding clamp Quando l'ATP si associa alla proteina clamp loader si legheranno e apriranno le sliding clamp, in modo che la sua struttura ad anello possa circondare il complesso DNA del primer-template. Una volta legato, il clamp loader idrolizza l'ATP ad ADP, causando la disassociazione del clamp loader e la chiusura del clamp intorno al DNA, la DNA polimerasi si lega quindi alle proteine clamp, e insieme, scorrono lungo il DNA teplate o stampo, che unisce la DNA polimerasi al filamento e ne aumenta la processività fino a 1, 000 nucleotidi. Questa maggiore processività consente alla DNA polimerasi di eseguire la replicazione continua del DNA sul filamento principale.Tuttavia, sul modello di filamento ritardo, un'altra DNA polimerasi esegue la replicazione discontinua del DNA in modo da consentire alla molecole DNA polimerasi di sintetizzare simultaneamente i filamenti di DNA principale e ritardo;questo processo è a volte descritto come il modello del trombone. Il filamento in ritardo e il suo stampo formano un anello quando la DNA polimerasi inizia la sintesi del frammento di Okazaki a partire dall'RNA primer. L'anello del DNA cresce da entrambe le direzioni mentre l'elicasi disavvolge il DNA e il filamento in ritardo viene sintetizzato.Quando la DNA polimerasi incontra il successivo RNA primer, si stacca dal filamento del template. Nel frattempo, il primase aggiunge un altro primer al filamento in ritardo, e l'anello di DNA crescente è rilasciato. Le proteine clamp e clamp loader, permettono alla DNA polimerasi di riassociarsi rapidamente allo stampo di DNA primer.La formazione e il successivo collasso del loop del DNA si ripete con la sintesi di ogni nuovo frammento di Okazaki.

<ol>
	<li>O'Donnell, Michael, Lance Langston e Bruce Stillman. "Principi e concetti della replicazione del DNA in batteri, archei ed eucaria." Prospettive di Cold Spring Harbor in Biologia 5, n. 7 (2013): a010108.</li>
	<li>Alberts, Bruce. "Replicazione e ricombinazione del DNA". Nature 421, n. 6921 (2003): 431.</li>
	<li>Kelch, Brian A., Debora L. Makino, Mike O'Donnell e John Kuriyan. "ATPasi del caricatore a pinza e l'evoluzione dei macchinari di replicazione del DNA." BMC Biology 10, n. 1 (2012): 34.</li>
	<li>Hedglin, Mark, Ravindra Kumar e Stephen J. Benkovic. "Morsetti di replicazione e caricatori di pinze". Prospettive di Cold Spring Harbor in Biologia 5, n. 4 (2013): a010165.</li>
	<li>Gardner, Andrew F. e Zvi Kelman. "Il meccanismo di replicazione del DNA come bersagli terapeutici". Frontiers in Molecular Biosciences 6 (2019): 35.</li>
</ol>

il replisoma

La replicazione del DNA viene effettuata da un grande complesso di proteine che agiscono in modo coordinato per ottenere una replicazione del DNA ad alta fedeltà. Insieme, questo complesso è noto come meccanismo di replicazione del DNA o replisoma.

La sintesi dei filamenti principali e ritardati è un processo altamente coordinato. Per spiegare questo, il "modello del trombone" è stato proposto da Bruce Alberts nel 1980. La formazione dell’anello del DNA inizia quando un primer viene sintetizzato sul filamento ritardato genitore. Il ciclo cresce con la sintesi di un frammento di Okazaki e infine si dissolve quando termina la sintesi del frammento. La DNA polimerasi si lega quindi a un altro primer e l'intero ciclo, dalla formazione dell'anello al collasso, si ripete. Il replisoma consente di coordinare tutte le attività come un complesso di macchinari di replicazione.

Componenti del replisoma

Le elicasi svolgono e separano il DNA a doppio filamento. Questi enzimi sono presenti come un singolo anello esamero nei procarioti e come un doppio anello esamero negli eucarioti. Le elicasi eucariotiche dipendono da proteine aggiuntive, Cdc45 e GINS, per funzionare. Le proteine leganti il DNA a filamento singolo (SSB) impediscono ai filamenti di DNA di ricomporsi. Nei procarioti, gli SSB sono costituiti da una singola subunità, mentre negli eucarioti sono una proteina eterotrimerica nota come proteina di replicazione A (RPA).

La primasi aggiunge un primer di RNA nel punto in cui avrà origine la sintesi del DNA. Nei procarioti, la primasi è presente come enzima a subunità singola chiamato DnaG, che sintetizza un primer di RNA di circa 12 nucleotidi. Negli eucarioti, un enzima multisubunità, la DNA polimerasi-α primasi, sintetizza un primer ibrido RNA-DNA di circa 25 nucleotidi. Oltre alla polimerasi-α, la polimerasi replicativa estenderà il DNA appena sintetizzato. Mentre nei procarioti è presente un singolo tipo di polimerasi replicativa, la DNA polimerasi III, negli eucarioti sono presenti due diversi tipi di polimerasi replicative, Pol ε e Pol δ, rispettivamente per la sintesi del filamento principale e del filamento ritardato.

Le proteine sliding clamp mantengono le polimerasi attaccate allo stampo di DNA. Il β-clamp, una proteina omodimerica, funge da morsetto nei procarioti. Negli eucarioti, lo stesso compito viene svolto dall'antigene nucleare delle cellule proliferanti (PCNA), una proteina omotrimerica. Il poro centrale della pinza scorrevole è carico positivamente, il che gli consente di avere interazioni elettrostatiche con la struttura fosfato del DNA caricata negativamente. La pinza è fissata al DNA mediante un caricatore a pinza. Queste proteine pentameriche appartengono alla classe AAA+ delle ATPasi. Il caricatore di pinze eucariotico è noto come fattore di replicazione C, mentre il caricatore di pinze procariotico di E. coli è noto come complesso γ. Tuttavia, si ritiene che le proteine sliding clamp e i caricatori del morsetto siano omologhi evolutivi, a differenza di molti altri componenti del replisoma.

Il Replisoma

La replicazione del DNA è effettuata da un grande complesso di proteine che agiscono in una materia coordinata per ottenere una replicazione del DNA ad alta fedeltà. Insieme questo ...

Education

Didattica

JoVE Core

Molecular Biology

Biologia Molecolare

Unit 1

Unità 1

DNA Replication

Replicazione del DNA

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

dna replication teams in the replisome

DNA replication depends on the replisome, a coordinated complex of proteins that copies DNA with high accuracy. This DNA replication machinery brings many parts together so the leading and lagging strands can be made at the same time.

A key idea in this process is the trombone model, proposed by Bruce Alberts in 1980. In this model, a loop forms on the lagging strand when a primer is made. The loop grows as an Okazaki fragment is synthesized, then falls apart when that fragment is finished. DNA polymerase then moves to a new primer, and the cycle repeats.

Helicases start the process by unwinding and separating double-stranded DNA. In prokaryotes, helicase is a single hexamer ring, while in eukaryotes it forms a double hexamer ring. Eukaryotic helicases also need the extra proteins Cdc45 and GINS to work. Single-stranded DNA binding proteins keep the separated strands from reannealing. In prokaryotes, these are SSB proteins with one subunit. In eukaryotes, the equivalent protein is replication protein A, or RPA, which is a heterotrimer.

Primase adds the RNA primer that gives DNA synthesis a starting point. In prokaryotes, primase is the single-subunit enzyme DnaG, and it makes an RNA primer of about 12 nucleotides. In eukaryotes, DNA polymerase-alpha primase makes an RNA-DNA hybrid primer of about 25 nucleotides. After that, the replicative polymerase extends the new DNA strand. Prokaryotes use DNA polymerase III, while eukaryotes use Pol epsilon for the leading strand and Pol delta for the lagging strand.

Sliding clamp proteins hold the polymerases on the DNA template so copying can continue efficiently. The prokaryotic beta-clamp is a homodimer, and the eukaryotic clamp is proliferating cell nuclear antigen, or PCNA, which is a homotrimer. The clamp has a positively charged central pore that interacts with the negatively charged DNA backbone. A clamp loader places the clamp onto DNA. These pentameric AAA+ ATPases include the eukaryotic replication factor C and the E. coli gamma complex. The clamp proteins and clamp loaders are thought to be evolutionary homologs, unlike many other replisome components.

DNA Replication Teams in the Replisome

replication in prokaryotes

Prokaryotic DNA Replication Steps

Prokaryotic DNA replication copies the chromosome before a cell divides. In bacteria, this process starts at a specific DNA site called the origin of replication. From there, the cell builds new DNA strands using enzymes that match each base with its partner. The DNA double helix first opens so replication can begin. As the strands separate, each original strand serves as a template. New nucleotides are added in a set order, which helps the cell make an accurate copy of its genetic material. <br...

replication in eukaryotes

Eukaryotic DNA Replication Steps

Eukaryotic DNA replication copies the genome before a cell divides. In eukaryotes, this process happens in a controlled sequence so each new cell can receive genetic information. Replication begins at specific sites on the DNA called origins. The DNA is opened, and each original strand serves as a template, meaning it guides the building of a new complementary strand. This sets up two DNA molecules from one original molecule. The process then continues as enzymes add matching nucleotides to...

dna base pairing

DNA Base Pair Rules

DNA base pairing follows specific rules that help DNA carry genetic information. In DNA, the bases pair in a regular way, with adenine matching thymine and cytosine matching guanine. These pairs fit together because of their chemical shapes and bonding patterns. These base pairs also support accurate DNA replication. When DNA copies itself, each strand can guide the formation of a new partner strand using the pairing rules. Understanding base pairing helps explain how DNA stays organized and...

the dna replication fork

DNA Replication Stress and Fork Stalling

DNA replication stress and fork stalling can disrupt the copying of a cell’s genome. The replication fork is the Y-shaped site where DNA strands separate and new complementary strands are made at the same time. This linked unwinding and synthesis helps cells duplicate DNA efficiently and with fewer errors. In organisms with small circular DNA, such as E. coli, replication often begins at a single origin. That setup creates two replication forks that move in opposite directions from the opening...

proofreading

Proofreading in DNA Replication

Proofreading in DNA replication helps keep DNA copying accurate. It is a built-in check that reduces mistakes as new DNA is made. DNA polymerase is the enzyme that carries out this checking during replication. When it adds a wrong nucleotide, it can remove the error and replace it with the correct one. This correction step helps maintain the correct DNA sequence. Proofreading is an important part of DNA replication because it supports genetic accuracy. By catching mistakes as they happen, the...

dna helicases

Helicase Motor Proteins in DNA Unwinding

Helicase motor proteins help unwind DNA during key cell processes. They use energy from ATP hydrolysis, which is the breakdown of ATP to release usable energy. This movement lets helicases separate DNA strands when the cell needs access to the genetic code. These enzymes are involved in DNA replication, repair, recombination, and transcription. Helicases are found in all living organisms, but their structure, function, and movement can differ. In prokaryotes, the DnaB helicase moves along the...

the replisome

DNA replication depends on the replisome, a coordinated complex of proteins that copies DNA with high accuracy. This DNA replication machinery brings many parts together so the leading and lagging strands can be made at the same time. A key idea in this process is the trombone model, proposed by Bruce Alberts in 1980. In this model, a loop forms on the lagging strand when a primer is made. The loop grows as an Okazaki fragment is synthesized, then falls apart when that fragment is finished.

lagging strand synthesis

Okazaki Fragments in DNA Replication

DNA replication uses a leading strand and a lagging strand, and they are made at different rates. The leading strand starts first. The lagging strand starts later, moves more slowly, and is made in pieces. The two strands also differ in direction and starting steps. Leading strand synthesis follows the opening replication fork. Lagging strand synthesis goes in the opposite direction. The leading strand needs one RNA primer, while the lagging strand needs multiple RNA primers. After priming,...

mismatch repair

Fixing DNA Copying Errors

Mismatch repair helps fix DNA copying errors after replication. When DNA is copied, small mistakes can slip through. This repair system finds those mismatches and corrects them before they become permanent changes. The process depends on a group of mutator proteins. These proteins work together to detect the error, remove the incorrect section, and help replace it with the proper DNA sequence. In this way, mismatch repair supports the accuracy of genetic information. If the repair system does...

dna topoisomerases

How Topoisomerases Untwist DNA

DNA topoisomerases are enzymes that untwist DNA when it becomes overcoiled during cell processes such as DNA replication and transcription. They help regulate positive and negative DNA supercoiling without changing the nucleotide sequence. Clockwise overwinding creates positively supercoiled DNA, while counterclockwise underwinding produces negatively supercoiled DNA. Topoisomerases are grouped into two main types. Type I topoisomerases act on one strand of double-stranded DNA, and they...

telomeres and telomerase

How Telomerase Protects Chromosome Ends

Telomerase helps protect chromosome ends during eukaryotic DNA replication. When the final primer is removed, a single-stranded DNA fragment can remain at the end of the chromosome. That piece cannot be copied in the same way as the rest of the strand because there is no 3' end for new DNA to attach to. If this end piece is not replaced, chromosomal DNA is gradually lost each time a cell divides. The exposed single-stranded DNA can also trigger a DNA damage response from enzymes that detect it.

non-nuclear inheritance

Cytoplasmic Inheritance in Cells

Cytoplasmic inheritance explains how some traits are passed through cell structures outside the nucleus. These traits come from organelles such as mitochondria and chloroplasts. They do not follow the usual nuclear pattern of inheritance. Mitochondria and chloroplasts each contain their own DNA. Because of this, they can carry genetic information that affects cell function and certain visible traits. In high school biology, this topic helps explain why not all inherited traits come from...

animal mitochondrial genetics

Animal Mitochondrial DNA and Inheritance

Animal mitochondrial DNA has its own genome, separate from nuclear DNA. It is a double-stranded, closed circular molecule with about 20,000 base pairs. One strand is the heavy, or H-strand, because it is rich in guanine. The other is the light, or L-strand, because it is rich in cytosine. Compared with nuclear DNA, mitochondrial DNA has very little non-coding sequence. It also has no introns. Its genes are packed closely together, and some even overlap. The D-loop is the main non-coding...

comparing mitochondrial, chloroplast, and prokaryotic genomes

comparing-mitochondrial-chloroplast-and-prokaryotic-genomes

How Organelle Genomes Resemble Bacteria

Mitochondrial and chloroplast genomes still keep several traits from their bacterial ancestors. They also show changes that happened after these organelles evolved inside eukaryotic cells. Eukaryotic cells are cells with a nucleus, while prokaryotes are cells without one. Like prokaryotic genomes, mitochondrial and chloroplast genomes do not bind with histone-like proteins. They also do not show the complex chromosome-like packaging seen in eukaryotes. Mitochondria and chloroplasts divide by...

export of mitochondrial and chloroplast genes

export-of-mitochondrial-and-chloroplast-genes

How Organelles Pass Genes to the Nucleus

Eukaryotic cells can carry three genetic systems: nuclear, mitochondrial, and chloroplast. Over time, many genes from mitochondria and chloroplasts have moved into the nucleus. In some plant species, this gene transfer is still happening. This movement has affected large parts of the genome in some organisms. About 18% of the Arabidopsis thaliana nuclear genome is thought to come from the chloroplast's cyanobacterial ancestor. In yeast, around 75% of the genome is derived from the...

single-strand dna binding proteins

How SSB Proteins Protect DNA Strands

Single-strand DNA-binding proteins, or SSB proteins, help protect DNA during replication. When double-stranded DNA is unwound, the two strands separate. SSB proteins bind to the exposed single strands and keep them stable. These proteins bind in a sequence-independent manner. That means the order of the nitrogenous bases does not have to follow a specific pattern for SSB proteins to attach. Their binding straightens single-stranded DNA and makes it more rigid. This support may help DNA...

key terms and concepts

Explore how the replisome coordinates DNA replication, from helicase and primase to polymerases, sliding clamps, and the trombone model.

DNA Replication Teams in the Replisome | JoVE K12

molecular biology

Le video animazioni di JoVE Core Molecular Biology, organizzate in video lezioni, illustrano i processi molecolari cellulari in maniera chiara e concisa. Inoltre, nei video di "scienziati in azione", i concetti scientifici vengono applicati e dimostrati da ricercatori attraverso esperimenti in laboratorio.

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Overview of Myosin Structure and Function

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1. Engage in evidence-based argument to relate a cell's function to the structure, function, and diversity of its components. Examples: Muscle cells have a large number of mitochondria, which create energy for contraction in the form of ATP. Some plant cells have a large vacuole which is used for storage and transport of excess nutrients in changing environments.

9-12.B.1.1

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RNA Structure

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Types of RNA

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Bacterial RNA Polymerase

Eukaryotic RNA Polymerases

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RNA Polymerase II Accessory Proteins

Transcription Elongation Factors

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Pre-mRNA Processing: RNA Splicing

Chromatin Structure and RNA Splicing

Alternative RNA Splicing

Nuclear Export of mRNA

Transfer RNA Synthesis

Ribosomal RNA Synthesis

The Nucleolus

Additional Subnuclear Structures

Translation

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tRNA Activation

Initiation of Translation

Termination of Translation

Improving Translational Accuracy

prokaryotic-transcriptional-activators-and-repressors

Prokaryotic Transcriptional Activators and Repressors

Nonsense-mediated mRNA Decay

The Eukaryotic Promoter Region

Molecular Chaperones and Protein Folding

Co-activators and Co-repressors

The Proteasome

Master Transcription Regulators

Regulated Protein Degradation

Regulated mRNA Transport

Proteins: From Genes to Degradation

mRNA Stability and Gene Expression

Cell Specific Gene Expression

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regulation-of-expression-occurs-at-multiple-steps

Regulation of Expression Occurs at Multiple Steps

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Cis-regulatory Sequences

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Cooperative Binding of Transcription Regulators

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2. Obtain and evaluate information to explain the role of DNA and RNA in transcription and translation leading to protein synthesis and cellular function.

9-12.B.1.2

Nucleic Acids and Nucleotides

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a. Use a model to describe the structure and sequence of DNA, including nucleotide structure, base pairing, and the structure of the helix.

9-12.B.1.2.a

DNA Replication Teams in the Replisome

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