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

يتم تضاعف دى إن أيه من خلال مُجمع متعدد البروتين منسق تنسيق عالى معروف بإسم آلية تضاعف ال دى إن أيه،00:00:08.420 00:00:12.470 أو ريبليسوم الذي يزيد من كفاءة تضاعف ال دى إن أيه. المكونات الأساسية للآلية هي هيليكاز بروتينات ربط ال دى إن أيه أحادى الشريط،00:00:21.810 00:00:28.810 دى إن أيه برايماز،مشبك منزلق،حامل المشبك و دى إن أيه بوليميراز متعددة. وهي كلها مرتبطة ببعضها البعض بالقرب من شوكة التضاعف.

دى إن أيه بوليميراز المتضاعف لديها محفز للتقدم المضطرد حوالي 10 نيوكليوتيدات والذى هو عدد النيوكليوتيدات 00:00:41.830 00:00:45.070 التى يمكنها إضافتها إلى الشريط الوليد قبل الانفصال عن الشريط القالب. هذا غير فعال للغاية لنسخ جينومات كاملة في إطار وقت معقول, وهذه المشكلة تم حلها بمساعدة بروتينات المشبك المنزلق. عندما يرتبط ال أيه تى بى ببروتين حامل المشبك 00:01:01.200 00:01:03.870 سوف يرتبطون بالمشبك المنزلق ويفتحوه بحيث التركيب شبيه بالخاتم يمكن أن يحيط بمُركب قالب الدى إن أيه برايمر.

بمجرد أن إرتبط حامل المشبك يحلل ال أيه تى بى 00:01:13.470 00:01:17.670 إلى أيه دى بى مما يتسبب في إنفصال حامل المشبك و إغلاق المشبك حول دى إن أيه. ثم يرتبط دى إن أيه بوليميراز ببروتينات المشبك. 00:01:24.450 00:01:28.020 ومعا ينزلقون على طول قالب ال دى إن أيه, رابطا دى إن أيه بوليميراز فى الشريط وتزيد التقدم المضطرد إلى ما يصل إلى 1000 نيوكليوتيد هذه الزيادة فى التقدم المضطرد يسمح دى إن أيه بوليميراز 00:01:41.420 00:01:44.990 لتنفيذ تضاعف مستمر لل دى إن أيه على الشريط المتقدم.

ومع ذلك على قالب الشريط المتباطىء دى إن أيه بوليميراز آخر يؤدى تضاعف متقطع لل دى إن أيه بطريقة تسمح دى إن أيه بوليميراز ان يخلّق الأشرطة المتقدمة والمتأخرة في وقت واحد. هذه العملية وصفت في بعض الأحيان بنموذج الترومبون. الشريط المتباطىء والقالب الخاص به.

يشكلا حلقة عندما يبدأ دى إن أيه بوليميراز تخليق اجزاء أوكازاكي من بادئة أر إن أيه. حلقة الدى إن أيه تنمو من كلا الاتجاهين بينما الهليكاز يفك دى إن أيه و الشريط المتباطىء يتم تخليقه. عندما يصادف ال دى إن أيه بوليميراز بادئة الحمض النووي الريبي التالية 00:02:31.540 00:02:34.420 ينفصل عن شريطا القالب.

وفي الوقت نفسه يضيف البريماز بادئة أخرى للشريط المتباطىء. و تتحرر حلقة الدى إن أيه المتنامية. بروتينات المشبك وحامل المشبك تسمح لدى إن أيه بوليميراز إعادة الاقتران بسرعة مع قالب الحمض النووي ذو البادئة.

تكوين و انهيار حلقة الحمض النووي دى إن ايه تتكرر مع تخليق كل جزء جديد من أجزاء أوكازاكي

<ol>
	<li>أودونيل ، مايكل ، لانس لانغستون ، وبروس ستيلمان. "مبادئ ومفاهيم تكرار الحمض النووي في البكتيريا والعتائق وحقيقيات النوى". وجهات نظر كولد سبرينج هاربور في علم الأحياء 5 ، العدد 7 (2013): a010108.</li>
	<li>ألبرتس ، بروس. "تكرار الحمض النووي وإعادة تركيبه". طبيعة سجية 421 ، رقم 6921 (2003): 431.</li>
	<li>كيلش ، بريان أ. ، ديبورا إل ماكينو ، مايك أودونيل ، وجون كوريان. "محمل المشبك ATPases وتطور آلية تكرار الحمض النووي." BMC Biology 10 ، رقم 1 (2012): 34.</li>
	<li>هيدجلين ، مارك ، رافيندرا كومار ، وستيفن جيه بينكوفيتش. "مشابك النسخ المتماثل ولوادر المشبك". وجهات نظر كولد سبرينج هاربور في علم الأحياء 5 ، العدد 4 (2013): a010165.</li>
	<li>غاردنر وأندرو ف. وزفي كيلمان. "آلية تكرار الحمض النووي كأهداف علاجية". الحدود في العلوم البيولوجية الجزيئية 6 (2019): 35.</li>
</ol>

الجسيم المكرر

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يتم تنفيذ تكرار الحمض النووي بواسطة مجموعة كبيرة من البروتينات التي تعمل في مادة منسقة لتحقيق تكرار الحمض النووي عالي الدقة. يُعرف هذا المجمع معًا بآلية تكرار الحمض النووي أو الريبوسوم.

يعد تركيب الخيوط الرائدة والمتأخرة عملية منسقة للغاية. لشرح ذلك، اقترح بروس ألبرتس "نموذج الترومبون" في عام 1980. يبدأ تكوين حلقة الحمض النووي عندما يتم تصنيع التمهيدي على الشريط الأصلي المتخلف. تنمو الحلقة مع تركيب شظية أوكازاكي وتذوب أخيرًا عندما ينتهي تركيب الشظية. ثم يرتبط بوليميراز الحمض النووي بمبدئ آخر وتتكرر الدورة بأكملها، بدءًا من تكوين الحلقة وحتى الانهيار. يسمح الريبوسوم بتنسيق جميع الأنشطة كمركب لآلات النسخ.

مكونات الريبوسوم

يتفكك الهيليكاز ويفصل الحمض النووي المزدوج الذي تقطعت به السبل. توجد هذه الإنزيمات كحلقة سداسية واحدة في بدائيات النوى وكحلقة سداسية مزدوجة في حقيقيات النوى. تعتمد الهيلكازات حقيقيات النواة على بروتينات إضافية، Cdc45 وGINS، لتعمل. تمنع بروتينات الربط الحمض النووي المفرد (SSB) خيوط الحمض النووي من إعادة التلدين. في بدائيات النوى، تتكون SSBs من وحدة فرعية واحدة، بينما في حقيقيات النوى، فهي عبارة عن بروتين غير متجانس يعرف باسم بروتين النسخ A (RPA).

يُضيف بريميزالتمهيدي للحمض النووي الريبي (RNA) إلى المكان الذي سينشأ فيه تخليق الحمض النووي. في بدائيات النوى، يوجد البريميز على شكل إنزيم وحدة فرعية واحدة يسمى DnaG، والذي يقوم بتركيب الحمض النووي الريبوزي التمهيدي المكون من حوالي 12 نيوكليوتيدات. في حقيقيات النوى، يقوم إنزيم متعدد الوحدات، DNA بوليميراز-ألفا بريميز، بتصنيع التمهيدي الهجين RNA-DNA المكون من حوالي 25 نيوكليوتيدات. بالإضافة إلى البوليميراز-α، فإن البوليميراز التكراري سيعمل على توسيع الحمض النووي المركب حديثًا. في حين أن نوع واحد من البوليميراز التكراري، DNA وهو بوليميراز الحمض النووي الثالث، موجود في بدائيات النوى، هناك نوعان مختلفان من البوليميراز التكراري، Pol ε وPol δ، موجودان في حقيقيات النوى، لتخليق الشريط الرئيسي والخيوط المتأخرة، على التوالي.

تحافظ بروتينات الكتيلة المنزلقة على البوليميرات المرتبطة بقالب الحمض النووي. β-clamp، وهو بروتين متجانس، يعمل كمشبك في بدائيات النوى. في حقيقيات النوى، يتم تنفيذ نفس المهمة عن طريق تكاثر المستضد النووي للخلية (PCNA)، وهو بروتين متجانس. إن المسام المركزي للمشبك المنزلق مشحون بشكل إيجابي، مما يمكنه من إجراء تفاعلات كهروستاتيكية مع العمود الفقري فوسفاتي المشحون سالبًا للحمض النووي. يتم الربط المشبك بالحمض النووي بواسطة محمل المشبك. تنتمي هذه البروتينات الخماسية إلى فئة AAA+ من ATPases. يُعرف محمل المشبك حقيقي النواة بعامل النسخ C، بينما يُعرف محمل المشبك E. coli بدائيات النواة باسم المركب γ؛ ومع ذلك، يُعتقد أن بروتينات المشبك ومحمل المشبك هي متماثلات تطورية على عكس العديد من المكونات الأخرى للريبوسوم.
</div>

يتم تكرار الحمض النووي بواسطة مجموعة كبيرة من البروتينات التي تعمل في مسألة منسقة لتحقيق تكرار الحمض النووي عالي الدقة. معا هذا ...

Education

JoVE Core

Molecular Biology

البيولوجيا الجزيئية

Unit 1

الوحدة الأولى

DNA Replication

تضاعف الحمض النووي (DNA)

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

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9-12.B.1.1

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Transfer RNA Synthesis

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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

MicroRNAs

MicroRNA (miRNA) are short, regulatory RNA transcribed from introns (non-coding regions of a gene) or intergenic regions (stretches of DNA present between ...

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

Regulation of Expression Occurs at Multiple Steps

Small interfering RNAs (siRNA)

Cis-regulatory Sequences

lncRNA - Long Non-coding RNAs

cooperative-binding-of-transcription-regulators

Cooperative Binding of Transcription Regulators

Epigenetic Regulation

Epigenetic changes alter the physical structure of the DNA without changing the genetic sequence and often regulate whether genes are turned on or off. ...

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

Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and have instructions for its ...

Nucleic Acid Structure

The pentose sugar in DNA is deoxyribose, while in RNA the pentose sugar is ribose. The difference between the sugars is the presence of the hydroxyl group ...

Genomic DNA in Prokaryotes

The genome of most prokaryotic organisms consists of double-stranded DNA organized into one circular chromosome in a region of cytoplasm called the ...

Genomic DNA in Eukaryotes

Eukaryotes have large genomes compared to prokaryotes. To fit their genomes into a cell, eukaryotic DNA is packaged extraordinarily tightly inside the ...

The DNA Helix

Overview

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most ...

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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