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

שכפול DNA בכרומוזומים אאוקריוטים מתחיל במספר מקורות של שכפול, אשר מזוהים וקשורים על ידי קומפלקס זיהוי המקור, או ORC.
לאחר מכן ORC מגייס מנחת מסוקים כדי לשחרר את הדנ"א, ומייצר בועת שכפול עם שני מזלגות שכפול.
שני המזלגות נעים בכיוונים מנוגדים ומשבשים את הנוקלאוזומים שלפניהם. נוקלאוזומים אלה מורכבים מחדש על גדילי הבת, תוך שמירה על מבנה הכרומטין.
בכל מזלג, פריימרים של RNA מספקים את האתר עבור DNA פולימראז כדי להאריך את הגדיל המוביל ואת קטעי אוקזקי של הגדיל המפגר.
אנזים RNase מסיר את הפריימרים האלה, והדנ"א פולימראז ממלא את החסר. לבסוף, ליגאז DNA אוטם את השברים יחד.
עם זאת, כאשר הפריימר האחרון מוסר מהגדיל המפגר בקצה הכרומוזום הליניארי, הוא מייצר מתיחה תלויה של הדנ"א של התבנית.
אנזים בשם טלומראז מרחיב את המתיחה הזו עם דנ"א שאינו מקודד כדי למנוע אובדן של דנ"א מקודד במהלך מחזורי השכפול הבאים.
השכפול נמשך עד שבועות השכפול הסמוכות מתמזגות והכרומוזום כולו משוכפל.

שכפול באיקריוטים

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בתאים אאוקריוטים, שכפול ה-DNA נשמר מאוד ומווסת היטב. יש לשכפל כרומוזומים ליניאריים מרובים בדיוק גבוה לפני חלוקת התא, ולכן ישנם חלבונים רבים הממלאים תפקידים מיוחדים בתהליך השכפול. שכפול מתרחש בשלושה שלבים: התחלה, התארכות וסיום, ומסתיים בשתי קבוצות שלמות של כרומוזומים בגרעין.

חלבונים רבים מתזמרים שכפול במקור

שכפול אאוקריוטי עוקב אחר רבים מאותם עקרונות כמו שכפול DNA פרוקריוטי, אך מכיוון שהגנום גדול בהרבה והכרומוזומים ליניאריים ולא מעגליים, התהליך דורש יותר חלבונים ויש לו כמה הבדלים עיקריים. ראשית, בניגוד לפרוקריוטים, שכפול באאוקריוטים מתרחש בו זמנית במספר מקורות שכפול לאורך כל כרומוזום. חלבוני יוזם מזהים ונקשרים למקורות אלו ומגייסים חלבוני הליקאז כדי לשחרר את הסליל הכפול של ה-DNA. בכל נקודת מוצא נוצרים שני מזלגות שכפול. לאחר מכן פרימאז מוסיף פריימרים קצרים של RNA לגדילים הבודדים של ה-DNA, המשמשים כנקודת מוצא ל-DNA פולימראז להיקשר ולהתחיל להעתיק את הרצף. ניתן לסנתז DNA רק בכיוון 5' עד 3', כך שכפול של שני הגדילים ממזלג שכפול בודד ממשיך בשני כיוונים שונים. הגדיל המוביל מסונתז ברציפות, בעוד שהגדיל המפגר מסונתז בקטעים קצרים של 100-200 זוגות בסיסים באורך, הנקראים שברי אוקאזקי. לאחר השלמת עיקר השכפול, אנזימי RNase מסירים את פריימרי ה-RNA, DNA פולימראז ממלא את הפערים, ו-DNA ליגאז אוטם את הפערים בגדיל החדש.

חלוקת עבודת השכפול בין פולימראזות

עומס העבודה של העתקת DNA באאוקריוטים מתחלק בין מספר סוגים שונים של אנזימי DNA פולימראז. משפחות עיקריות של פולימראזות DNA על פני כל האורגניזמים מסווגות לפי הדמיון של מבני החלבון ורצפי חומצות האמינו שלהם. המשפחות הראשונות שהתגלו כונו A, B, C ו-X, כאשר המשפחות Y ו-D זוהו מאוחר יותר. פולימראזות משפחתיות B באוקריוטות כוללות את Pol α, שמתפקד גם כפרימאז במזלג השכפול, ו-Pol δ ו-ε, האנזימים שעושים את רוב העבודה של שכפול ה-DNA על הגדילים המובילים והמאחרים של התבנית, בהתאמה. פולימראזות DNA אחרות אחראיות למשימות כגון תיקון נזקי DNA, העתקת DNA מיטוכונדריאלי ופלסטידי, ומילוי פערים ברצף ה-DNA על הגדיל המאחר לאחר הסרת פריימרים של ה-RNA.

טלומרים מגנים על קצוות הכרומוזומים מפני דגרדציה

מכיוון שהכרומוזומים האוקריוטיים הם ליניאריים, הם רגישים לפירוק בקצוות. כדי להגן על מידע גנטי חשוב מנזק, קצוות הכרומוזומים מכילים חזרות רבות שאינן מקודדות של DNA שמור מאוד העשיר ב-G, הטלומרים. תליה קצרה חד-גדילית 3' בכל קצה של הכרומוזום מקיימת אינטראקציה עם חלבונים מיוחדים, המייצבים את הכרומוזום בתוך הגרעין. בגלל האופן שבו מסונתז הגדיל המאחר, לא ניתן לשכפל כמות קטנה מה-DNA הטלומרי עם כל חלוקת תא. כתוצאה מכך, הטלומרים מתקצרים בהדרגה במהלך מחזורי תאים רבים, וכך ניתן למדוד אותם כסמן להזדקנות התא. אוכלוסיות מסוימות של תאים, כמו תאי נבט ותאי גזע, מבטאות טלומראז, אנזים שמאריך את הטלומרים, ומאפשר לתא לעבור יותר מחזורי תאים לפני שהטלומרים מתקצרים.
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בתאים אאוקריוטים, שכפול הדנ"א נשמר מאוד ומווסת היטב. כרומוזומים ליניאריים מרובים חייבים להיות משוכפלים בנאמנות גבוהה לפני ...

Education

JoVE Core

Anatomy and Physiology

אנטומיה ופיזיולוגיה

Unit 1

יחידה 1

Essential Cellular Processes

תהליכים תאיים חיוניים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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

Central Dogma: DNA to Protein

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

RNA Types in Gene Expression

RNA types play different roles in gene expression. RNA, or ribonucleic acid, helps carry and use genetic information in cells. The main types discussed here are messenger RNA, ribosomal RNA, and transfer RNA. Messenger RNA, or mRNA, carries the genetic code from DNA to the ribosome. The ribosome is the site where proteins are made. Ribosomal RNA, or rRNA, is a key part of the ribosome itself. Transfer RNA, or tRNA, brings the correct amino acids to the ribosome during protein building. These...

transcription

Transcription and RNA Synthesis

Transcription is the process of making RNA from a DNA template. It is a key step in gene expression, because cells use the DNA sequence to build an RNA copy that can carry the message forward. During transcription, RNA polymerase binds to DNA and reads one strand as the template. The enzyme links RNA nucleotides together in the correct order to form a growing RNA molecule. This copying step does not make DNA; it produces RNA. The transcript focuses on the central idea of transcription as DNA...

translation

Translation: mRNA to Protein

Translation is the step in gene expression where ribosomes use messenger RNA, or mRNA, to build a protein. The mRNA sequence carries the instructions copied from DNA. During translation, those instructions are read in order so the cell can make a specific chain of amino acids. This process depends on the ribosome and transfer RNA, or tRNA. The ribosome reads the mRNA, and tRNA brings the matching amino acids. As the chain grows, the amino acids are linked together to form a polypeptide, which...

regulation of expression at multiple steps

regulation-of-expression-at-multiple-steps

How Cells Control Gene Expression

Cells control gene expression at several stages, from making RNA to building protein. These checkpoints include transcription, RNA processing, RNA localization, and translation. Together, they help decide when a gene is used and whether a protein is made. Transcription is controlled by regulatory proteins. Transcription factors, activators, and repressors can start or slow the transcription of genes. After transcription, the cell makes a precursor RNA, also called pre-mRNA. Pre-mRNA must be...

what is the cell cycle?

Cell Cycle Stages in Cell Growth

The cell cycle is the process that controls cell growth and division. It explains how one cell makes two new cells. This process helps cells grow and reproduce.

interphase

Interphase and Cell Growth

Interphase is the part of the cell cycle when a cell grows and prepares to divide. It is a major stage of the cell cycle, and it comes before cell division begins. During interphase, the cell carries out its normal functions. It also copies its DNA so each new cell can receive a full set of genetic material. The cell may also build up the materials it needs for division. Interphase is not a single step. It includes phases such as G1, S, and G2, which help the cell grow, copy DNA, and get...

mitosis and cytokinesis

Cell Division: Mitosis and Cytokinesis

Cell division depends on mitosis and cytokinesis. Mitosis is the stage when the cell’s nucleus divides and the copied chromosomes are separated into two sets. Cytokinesis is the step that follows and splits the cell into two daughter cells. These two processes work together to make sure each new cell receives genetic material and its own cytoplasm. Mitosis keeps the chromosome sets organized, while cytokinesis finishes the division of the whole cell. Together, they create two separate cells...

the cell cycle control system

Cell Cycle Checkpoints and Cyclin Control

The cell cycle is controlled by checkpoints that help a cell move from one phase to the next and begin mitosis. This control system uses internal regulatory molecules and outside signals to send stop or advance instructions. It makes sure each step is finished before the cell moves forward. Cyclins and cyclin-dependent kinases, or Cdks, are the main regulators of the cell cycle. They act during the G1, G2, and M phases. These regulators work at specific checkpoints to keep cell division...

molecular factors affecting cell division

molecular-factors-affecting-cell-division

Cell Cycle Regulators That Control Division

Cell division is controlled by outside signals and by internal cell cycle regulators. Nearby cell death can encourage division, and human growth hormone (hGH) can also promote it. In contrast, too little hGH or crowded cells can slow or stop division. Inside the cell, regulator molecules help each stage finish correctly before the next stage begins. Some regulators act directly on the cycle, while others affect the activity or production of other regulatory proteins. These molecules can either...

what is meiosis?

Meiosis and the Formation of Gametes

Meiosis is the cell division process that forms gametes, or sex cells. It reduces the chromosome number so offspring can inherit the correct amount of genetic material. This process includes two successive divisions. First, one cell divides, and then the resulting cells divide again. These steps separate the genetic material in a controlled way. Meiosis helps explain how sexual reproduction passes traits from one generation to the next. It is a key topic in high school biology because it...

overview of cell signaling

Cell Signaling Pathways and Responses

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...

types of signaling molecules

Chemical Messengers in Cell Signaling

Chemical messengers help cells communicate during signaling. These signaling molecules carry information from one cell to another and guide how cells respond. Some signaling molecules are gases, while others are proteins or peptides. Small lipids can also act as signals. In addition, cells may use steroids, amino acids, and even ions as signaling molecules. Each type of signaling molecule has different properties and works in a different way. Together, these molecules let cells send specific...

g protein-coupled receptors

G Protein-coupled Receptor Signaling

G protein-coupled receptors are a major class of cell-surface receptors. They help cells detect signals outside the cell and pass that information inward. These receptors are important in many kinds of cell communication. When a signal binds to a G protein-coupled receptor, the receptor changes shape. That change activates a G protein inside the cell. The activated G protein can then start a signaling pathway. This signaling system includes the receptor, the G protein, and the downstream...

cellular differentiation

From Stem Cell to Specialized Cells

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

The gene expression in cells is regulated at different stages: (i) transcription, (ii) RNA processing, (iii) RNA localization, and (iv) translation. ...

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

What is Meiosis?

Meiosis I

Meiosis is the division of a diploid cell into haploid cells forming sperm and eggs in animals through differentiation. Meiosis I is the first stage of ...

Meiosis II

Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for ...

Crossing over

Nondisjunction

Genome Copying Errors

DNA replication is a well-evolved process that copies millions of base pairs with high fidelity during each cell division. Occasionally a wrong base or a ...

Overview of DNA Repair

In order to be passed through generations, genomic DNA must be undamaged and error-free. However, every day, DNA in a cell undergoes several thousand to a ...

Base Excision Repair

One of the common DNA damages is the chemical alteration of single bases by alkylation, oxidation, or deamination. The altered bases cause mispairing and ...

RNA Editing

RNA editing is a post-transcriptional modification where a precursor mRNA (pre-mRNA) nucleotide sequence is changed by base insertion, deletion, or ...

Mutations

Teratogenicity

The ability of a drug to produce structural deformations and functional abnormalities in the developing embryo or the fetus is called teratogenicity, and ...

Mechanisms of Retrovirus-induced Cancers

Retroviruses are RNA viruses that have been shown to cause cancers in diverse species, including chickens, mice, cats, and monkeys. The RNA genomes of ...

Construct an argument based on evidence to support the claim that inheritable genetic variations may result from:New genetic combinations through meiosis (crossing over, nondisjunction), Non-lethal errors occurring during replication (insertions, deletions, substitutions), Heritable mutations caused by environmental factors (radiation, chemicals, and viruses)

SB2.b

Transgenic Plants

Recombinant DNA technology called transgenesis is often used to add a foreign gene or remove a detrimental gene from an organism. Such genetically ...

Transgenic Organisms

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Transgenic organisms are genetically engineered to carry transgenes&#x2014;genes from a different species&#x2014;as part of their genome. The ...

Testing For Genetically Modified Foods

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
Genetic modification of foods has been a controversial issue due to debated ...

Genetic Engineering of Model Organisms

Transgenesis, or the use of genetic engineering to alter gene expression, is widely used in the field of developmental biology. Scientists use a number of ...

Ask questions to gather and communicate information about the use and ethical considerations of biotechnology in forensics, medicine, and agriculture

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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