Name: eukaryotic dna copying at the replication fork
Uploaded: 2023-06-23T15:38:45.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

Georgia Standards of Excellence

9-12

Biology

SB2.a

Replication in Eukaryotes

La replicazione del DNA nei cromosomi eucariotici inizia a più origini di replicazione, che sono identificate e legate dal complesso di riconoscimento dell'origine, o ORC.
L'ORC recluta quindi elicasi per svolgere il DNA, producendo una bolla di replicazione con due forcelle di replicazione.
Le due forcelle si muovono in direzioni opposte e distruggono i nucleosomi davanti a loro. Questi nucleosomi vengono poi riassemblati sui filamenti figli, mantenendo la struttura della cromatina.
Ad ogni forchetta, i primer dell'RNA forniscono il sito per la DNA polimerasi per allungare il filamento principale e i frammenti di Okazaki del filamento in ritardo.
Un enzima RNasi rimuove quindi questi primer e la DNA polimerasi riempie le lacune. Infine, la DNA ligasi sigilla insieme i frammenti.
Tuttavia, quando l'ultimo primer viene rimosso dal filamento in ritardo alla fine del cromosoma lineare, produce un tratto sporgente del DNA stampo.
Un enzima chiamato telomerasi estende questo tratto sporgente con DNA non codificante per prevenire la perdita di DNA codificante durante i successivi cicli di replicazione.
La replicazione continua fino a quando le bolle di replicazione adiacenti si fondono e l'intero cromosoma viene duplicato.

replicazione negli eucarioti

Nelle cellule eucariotiche, la replicazione del DNA è altamente conservata e strettamente regolata. Più cromosomi lineari devono essere duplicati con alta fedeltà prima della divisione cellulare, quindi ci sono molte proteine che svolgono ruoli specializzati nel processo di replicazione. La replica avviene in tre fasi: inizio, allungamento e terminazione e finisce con due serie complete di cromosomi nel nucleo.

Molte proteine orchestrano la replicazione all’origine

La replicazione eucariotica segue molti degli stessi principi della replicazione del DNA procariotico ma, siccome il genoma è molto più grande e i cromosomi sono lineari anziché circolari, il processo richiede più proteine e presenta alcune differenze fondamentali. Innanzitutto, a differenza dei procarioti, la replicazione negli eucarioti avviene simultaneamente in più origini di replicazione lungo ciascun cromosoma. Le proteine iniziatrici riconoscono e si legano a queste origini e reclutano proteine elicasi per svolgere la doppia elica del DNA. In ogni punto di origine si formano due forcelle replicative. La primase aggiunge quindi brevi primer di RNA ai singoli filamenti di DNA, che servono come punto di partenza affinché la DNA polimerasi si leghi e inizi a copiare la sequenza. Il DNA può essere sintetizzato solo nella direzione da 5' a 3', quindi la replicazione di entrambi i filamenti da una singola forca di replicazione procede in due direzioni diverse. Il filamento principale viene sintetizzato in modo continuo, mentre il filamento ritardato viene sintetizzato in brevi tratti di 100-200 paia di basi di lunghezza, chiamati frammenti di Okazaki. Una volta completata la maggior parte della replicazione, gli enzimi RNasi rimuovono i primer dell'RNA, la DNA polimerasi riempie gli spazi vuoti e la DNA ligasi sigilla gli spazi vuoti nel nuovo filamento.

Divisione del lavoro di replica tra le polimerasi

Il carico di lavoro della copia del DNA negli eucarioti è suddiviso tra più tipi diversi di enzimi della DNA polimerasi. Le principali famiglie di DNA polimerasi in tutti gli organismi sono classificate in base alla somiglianza delle loro strutture proteiche e delle sequenze di amminoacidi. Le prime famiglie ad essere scoperte furono chiamate A, B, C e X, mentre le famiglie Y e D furono identificate successivamente. Le polimerasi della famiglia B negli eucarioti includono Pol α, che funziona anche come primasi sulla forca di replicazione, e Pol δ e ε, gli enzimi che svolgono la maggior parte del lavoro di replicazione del DNA rispettivamente sui filamenti principali e ritardati dello stampo. Altre DNA polimerasi sono responsabili di compiti come la riparazione del danno al DNA, la copia del DNA mitocondriale e plastidico e il riempimento delle lacune nella sequenza del DNA sul filamento in ritardo dopo la rimozione dei primer dell'RNA.

I telomeri proteggono le estremità dei cromosomi dalla degradazione

Siccome i cromosomi eucariotici sono lineari, sono suscettibili alla degradazione alle estremità. Per proteggere importanti informazioni genetiche dai danni, le estremità dei cromosomi contengono molte ripetizioni non codificanti di DNA ricco di G altamente conservato, i telomeri. Una breve sporgenza 3' a filamento singolo su ciascuna estremità del cromosoma interagisce con proteine specializzate, che stabilizzano il cromosoma all'interno del nucleo. A causa del modo in cui viene sintetizzato il filamento ritardato, una piccola quantità di DNA telomerico non può essere replicata ad ogni divisione cellulare. Di conseguenza, i telomeri si accorciano gradualmente nel corso di molti cicli cellulari e quindi possono essere misurati come un indicatore dell’invecchiamento cellulare. Alcune popolazioni di cellule, come le cellule germinali e le cellule staminali, esprimono la telomerasi, un enzima che allunga i telomeri, consentendo alla cellula di sottoporsi a più cicli cellulari prima che i telomeri si accorcino.

Replicazione negli eucarioti

Nelle cellule eucariotiche, la replicazione del DNA è altamente conservata e strettamente regolata. I cromosomi lineari multipli devono essere duplicati con alta fedeltà prima ...

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JoVE Core

Anatomy and Physiology

Anatomia e Fisiologia

Unit 1

Unità 1

Essential Cellular Processes

Processi cellulari essenziali

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

eukaryotic dna copying at the replication fork

Eukaryotic DNA copying happens at replication forks, where the two DNA strands separate and new strands are built. This process lets a cell make an exact copy of its genetic material before it divides.

The transcript explains that eukaryotic replication follows the same basic steps seen in other DNA replication systems, but it takes place in cells with a nucleus. The replication machinery works on each separated strand as a template, so the new DNA matches the original sequence.

This topic is important for high school biology because it connects DNA structure to cell division and inheritance. Understanding replication in eukaryotes helps students see how genetic information is passed on when body cells grow and reproduce.

Eukaryotic DNA Copying at the Replication Fork

eukaryotic-dna-copying-at-the-replication-fork

the central dogma

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The central dogma explains how genetic information flows in cells from DNA to RNA to protein. It is a core idea in molecular biology and helps show how genes influence cell function. DNA stores the instructions. During transcription, a cell copies a gene into RNA, which is a related nucleic acid. That RNA message can then be used in translation to build a protein. Proteins carry out many jobs in cells and help determine traits. The central dogma links the genetic code in DNA to the molecules...

replication in eukaryotes

Eukaryotic DNA copying happens at replication forks, where the two DNA strands separate and new strands are built. This process lets a cell make an exact copy of its genetic material before it divides. The transcript explains that eukaryotic replication follows the same basic steps seen in other DNA replication systems, but it takes place in cells with a nucleus. The replication machinery works on each separated strand as a template, so the new DNA matches the original sequence. This topic is...

types of rna

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regulation of expression at multiple steps

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the cell cycle control system

Cell Cycle Checkpoints and Cyclin Control

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molecular factors affecting cell division

molecular-factors-affecting-cell-division

Cell Cycle Regulators That Control Division

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overview of cell signaling

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Cell signaling pathways and responses help cells communicate and react to changes. Cells send signals to one another, and those signals can trigger a specific response in the target cell. A signal usually begins when a signaling molecule reaches a cell with the right receptor, which is a protein that receives the message. The receptor helps the cell recognize the signal and start the communication process. Inside the cell, the message can move through a signaling pathway. This pathway passes...

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cellular differentiation

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Cellular differentiation turns unspecialized cells into specialized cells with specific jobs. This process helps a complex organism, such as a human, develop from a single fertilized egg into a body with many cell types. Nerve cells, muscle cells, and epithelial cells are examples of the final cell types that appear during development. A zygote is the first cell after fertilization. It is a totipotent stem cell, which means it has very high differentiation potential and can form all cell types...

key terms and concepts

Learn how eukaryotic DNA is copied at replication forks, where strands separate and new DNA is built before cell division in nucleus-containing cells.

Eukaryotic DNA Copying at the Replication Fork | JoVE K12

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

The Central Dogma

Types of RNA

Transcription

Translation

Regulation of Expression at Multiple Steps

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Construct an explanation of how the structures of DNA and RNA lead to the expression of information within the cell via the processes of replication, transcription, and translation

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SB2.b

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SB2.c

Obtain, evaluate, and communicate information to analyze how genetic information is expressed in cells

Eukaryotic DNA Copying at the Replication Fork

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