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

يبدأ تكرار الحمض النووي في الكروموسومات حقيقية النواة في أصول متعددة للنسخ المتماثل ، والتي يتم تحديدها وارتباطها بمركب التعرف على الأصل ، أو ORC.
يقوم ORC بعد ذلك بتجنيد الهليكازات لفك الحمض النووي ، مما ينتج عنه فقاعة نسخ متماثل مع شوكتين للنسخ المتماثل.
تتحرك الشوكتان في اتجاهين متعاكسين وتعطل النيوكليوسومات التي أمامهم. ثم يتم إعادة تجميع هذه النيوكليوسومات على خيوط الابنة ، مع الحفاظ على بنية الكروماتين.
في كل شوكة ، توفر بادئات الحمض النووي الريبي موقعا لبوليميراز الحمض النووي لإطالة الخيط الرئيسي وشظايا أوكازاكي من الخيط المتأخر.
ثم يزيل إنزيم RNase هذه البادئات ، ويملأ بوليميراز الحمض النووي الفجوات. أخيرا ، يغلق DNA ligase الشظايا معا.
ومع ذلك ، عندما تتم إزالة التمهيدي الأخير من الخيط المتأخر في نهاية الكروموسوم الخطي ، فإنه ينتج امتدادا متدلا من الحمض النووي للقالب.
إنزيم يسمى التيلوميراز يمتد هذا التمدد المتدلي مع الحمض النووي غير المشفر لمنع فقدان الحمض النووي المشفر أثناء دورات النسخ المتماثل اللاحقة.
يستمر النسخ المتماثل حتى تندمج فقاعات النسخ المتماثل المجاورة ويتم تكرار الكروموسوم بالكامل.

النسخ المتماثل في حقيقيات النوى

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في الخلايا حقيقية النواة، يتم الحفاظ على تضاعف الحمض النووي بشكل كبير وتنظيمه بإحكام. يجب أن تتضاعف الكروموسومات الخطية المتعددة بدقة عالية قبل انقسام الخلايا، لذلك هناك العديد من البروتينات التي تؤدي أدوارًا متخصصة في عملية التكاثر. يحدث التضاعف على ثلاث مراحل: البداية، والاستطالة، والإنهاء، وينتهي بـ مجموعتين كاملتين من الكروموسومات في النواة.

تقوم العديد من البروتينات بتنسيق التضاعف المتماثل في الأصل

يتبع تكاثر حقيقيات النواة العديد من المبادئ نفسها التي يتبعها تضاعف الحمض النووي بدائيات النواة، ولكن نظرًا لأن الجينوم أكبر بكثير والكروموسومات خطية وليست دائرية، فإن العملية تتطلب المزيد من البروتينات ولها بعض الاختلافات الرئيسية. أولاً، على عكس بدائيات النوى، يحدث التضاعف في حقيقيات النوى بشكل متزامن عند أصول متعددة للتضاعف على طول كل كروموسوم. تتعرف البروتينات البادئة على هذه الأصول وترتبط بها وتقوم بتجنيد بروتينات الهليكاز لتفكيك الحلزون المزدوج للحمض النووي. عند كل نقطة أصل، يتم تشكيل شوكتين متماثلتين. يضيف Primase بعد ذلك بادئات قصيرة من الحمض النووي الريبوزي (RNA) إلى خيوط الحمض النووي المفردة، والتي تكون بمثابة نقطة بداية لربط بوليميراز الحمض النووي والبدء في نسخ التسلسل. لا يمكن تصنيع الحمض النووي إلا في الاتجاه 5' إلى 3'، لذا فإن تضاعف كلا الشريطين من شوكة التضاعف الواحدة يستمر في اتجاهين مختلفين. يتم تصنيع الشريط الرئيسي بشكل مستمر، في حين يتم تصنيع الشريط المتأخر في فترات قصيرة يبلغ طولها من 100 إلى 200 زوج أساسي، تسمى أجزاء أوكازاكي. بمجرد اكتمال الجزء الأكبر من التكاثر، تقوم إنزيمات RNase بإزالة بادئات الحمض النووي الريبوزي (RNA)، ويملأ بوليميراز الحمض النووي الفجوات، ويقوم ليجاز الحمض النووي بسد الفجوات في الشريط الجديد.

تقسيم عمل التضاعف بين البوليمرات

ينقسم عبء عمل نسخ الحمض النووي في حقيقيات النوى بين عدة أنواع مختلفة من إنزيمات بوليميريز الحمض النووي. يتم تصنيف العائلات الرئيسية لبوليميرازات الحمض النووي في جميع الكائنات الحية حسب تشابه بنياتها البروتينية وتسلسلات الأحماض الأمينية. كانت العائلات الأولى التي تم اكتشافها تسمى A وB وC وX، وتم تحديد العائلتين Y وD لاحقًا. تشتمل بوليمرات العائلة B في حقيقيات النوى على Pol α، الذي يعمل أيضًا كبريماز في شوكة التضاعف، وPol δ وε، الإنزيمات التي تقوم بمعظم عمل تضاعف الحمض النووي على الخيوط الأمامية والمتأخرة للقالب، على التوالي. تكون بوليميرازات الحمض النووي الأخرى مسؤولة عن مهام مثل إصلاح تلف الحمض النووي، ونسخ الحمض النووي للميتوكوندريا والبلاستيد، وملء الفجوات في تسلسل الحمض النووي على الشريط المتأخر بعد إزالة بادئات الحمض النووي الريبوزي (RNA).

التيلوميرات تحمي نهايات الكروموسومات من التدهور

نظرًا لأن الكروموسومات حقيقية النواة خطية، فهي عرضة للتدهور في الأطراف. ولحماية المعلومات الوراثية المهمة من التلف، تحتوي نهايات الكروموسومات على العديد من التضاعفات الغير المشفرة للحمض النووي الغني بـ G المحفوظ بدرجة عالية، والذي يسمى التيلوميرات. يتفاعل جزء قصير مفرد بطول 3 بوصات عند كل طرف من الكروموسوم مع البروتينات المتخصصة، التي تعمل على تثبيت الكروموسوم داخل النواة. بسبب الطريقة التي يتم بها تصنيع الشريط المتأخر، لا يمكن تضاعف كمية صغيرة من الحمض النووي التيلوميري مع كل انقسام خلية. ونتيجة لذلك، تصبح التيلوميرات أقصر تدريجيًا على مدار العديد من دورات الخلية، وبالتالي يمكن قياسها كعلامة على شيخوخة الخلايا. مجموعات معينة من الخلايا، مثل الخلايا الجرثومية والخلايا الجذعية، تعبر عن التيلوميراز، وهو إنزيم يطيل التيلوميرات، مما يسمح للخلية بالخضوع لدورات خلوية أكثر قبل تقصير التيلوميرات.
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في الخلايا حقيقية النواة ، يتم الحفاظ على تكرار الحمض النووي بشكل كبير وتنظيمه بإحكام. يجب تكرار الكروموسومات الخطية المتعددة بدقة عالية قبل ...

Education

JoVE Core

Anatomy and Physiology

التشريح وعلم وظائف الأعضاء

Unit 1

الوحدة الأولى

Essential Cellular Processes

العمليات الخلوية الأساسية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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

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RNA Editing

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Mutations

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SB2.b

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Transgenic Organisms

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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

Description

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