Name: chromatin rebuilding during dna replication
Uploaded: 2021-04-07T12:12:01.000Z
Duration: 2 min 5 s
Channel: JoVE

진핵 세포의 유전 물질인 DNA는 염색체라고 하는 선형 구조로 핵 내부에 존재합니다.
염색체 내에서 이중 가닥 DNA는 주로 히스톤이라고 하는 옥타머 핵 단백질을 감싸서 뉴클레오솜을 형성합니다. 여러 비히스톤 단백질도 DNA와 결합하여 DNA 패키징을 돕습니다.
이러한 뉴클레오솜과 비히스톤 단백질은 코일을 형성하기 위해 배열되어 어레이에서 루프로 더 접혀 패킹된 염색질을 형성합니다. 염색질 압축의 정도는 매우 긴 DNA가 핵 내부에 들어갈 수 있도록 합니다. M 상 동안, 염색질은 응축 된 염색체를 형성하기 위해 더 코일을 감습니다.
염색체 복제는 전체 염색질 구조를 복제하는 것을 포함하므로 DNA와 염색질 관련 단백질이 모두 복제됩니다. 히스톤의 생산은 새로 합성된 DNA를 염색체로 패키징하는 데 필요한 추가 단백질을 생성하기 위해 증가합니다.
복제된 염색체의 정확한 염색질 구조를 복제하는 것은 유전자 조절에 필수적입니다. 
염색체 내에서 염색질 패키징 수준이 항상 균일한 것은 아닙니다. 염색체는 헤테로크로마틴(heterochromatin)이라고 하는 단단히 채워진 염색질이 있는 영역과 유크로마틴(euchromatin)이라고 하는 느슨하게 채워진 염색질이 있는 영역을 포함합니다.
헤테로크로마틴 DNA는 전사 기계에 접근할 수 없기 때문에 해당 영역의 유전자는 규칙적으로 전사되지 않습니다. 대조적으로, 유크로마틴 내의 DNA는 더 쉽게 접근할 수 있으므로 이 영역의 유전자를 전사할 수 있습니다. 
염색질의 이러한 구조적, 기능적 중요성으로 인해 염색체 복제 중에 전체 염색질 구조가 정확하게 재생되는 것이 중요합니다.

<ol>
	<li>그로스, 아냐, 월터 로샤, 알랭 베로, 주네비에브 알무즈니. "DNA 복제 및 복구 중 염색질 문제." Cell 128 (4)2007: 721–33. [<a href="https://www.sciencedirect.com/science/article/pii/S0092867407001298">출처</a>]</li>
	<li>Margueron, Raphaël 및 Danny Reinberg. "염색질 구조와 후성 유전 학적 정보의 상속." Nature Reviews Genetics 11 (4) 2010 : 285–96. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3760772/">출처</a>]</li>
</ol>

염색질 구조의 복제

Duplication of Chromatin Structure

세포 분열 중 염색체 복제 과정에는 게놈 전체의 파괴와 염색질의 재조립이 필요합니다. 염색질 구조는 계보 전파를 보장하기 위해 딸 세포에서 정확하게 유전되고, 재조립되고, 유지되어야 합니다.

염색질의 기본 단위는 뉴클레오솜으로, 팔량체 히스톤 단백질을 감싸고 있는 DNA와 개별 뉴클레오솜을 분리하는 짧은 연결 DNA로 구성됩니다. 뉴클레오솜 내의 히스톤 단백질은 N 말단이 코어 밖으로 돌출되어 있어 염색질 구조와 기능을 조절하는 다양한 공유 결합 변형 부위를 제공합니다.

복제하는 동안 DNA가 풀리면서 모 뉴클레오솜이 파괴되고 히스톤 단백질이 방출됩니다. 복제가 진행되고 딸 가닥이 형성됨에 따라 S기 동안 합성된 모 히스톤과 추가 히스톤 단백질이 조립되어 뉴클레오솜이 형성됩니다.

DNA의 히스톤 및 기타 후성유전 도메인의 번역 후 변형도 딸 게놈에서 충실하게 재현됩니다.

염색질 구조는 유전자 발현에 영향을 미칩니다

조절 및 코딩 DNA 서열이 대부분 뉴클레오솜 내에 숨겨져 존재하기 때문에 세포 내에서 게놈의 주요 부분은 전사 인자에 접근할 수 없는 상태로 남아 있습니다. 유전자가 발현되려면 전사 인자가 결합할 수 있는 접근 가능한 부위를 만들고 히스톤을 변형하여 염색질 구조를 재구성하고 전사가 허용되는 환경을 조성해야 합니다.

특정 조절 인자 복합체는 뉴클레오솜의 치환 또는 파괴에 의해 염색질의 국소 영역을 여는 데 관여합니다. 히스톤 꼬리의 번역 후 변형은 활성 또는 비활성 전사 상태를 유지하는 역할을 합니다. 히스톤 꼬리의 특정 변형은 DNA 압축 수준을 완화하여 뉴클레오솜의 불안정화 및 이동을 촉진하고 전사 기계가 유전자 발현에 영향을 미칠 수 있는 접근을 제공합니다.

세포 분열 중 염색체 복제 과정은 게놈 전체의 파괴와 염색질의 재조립을 필요로 합니다. 염색질 구조는 ...

Education

교육

JoVE Core

Molecular Biology

분자생물학

Unit 2

제2단원

Cell Division

세포 분열

KEY TERMS AND CONCEPTS

주요 용어 및 개념

chromatin rebuilding during dna replication

Chromatin rebuilding during DNA replication helps cells copy DNA and pass on chromosome structure to daughter cells. During cell division, the genome must be disrupted and then reassembled across the whole chromosome. This process allows chromatin to be inherited, rebuilt, and maintained in new cells.

The basic unit of chromatin is the nucleosome. A nucleosome contains DNA wrapped around an octamer of histone proteins, with short linker DNA between neighboring nucleosomes. The histone proteins have N-terminal tails that stick out from the core. These tails can receive covalent modifications that help control chromatin structure and function.

As DNA unwinds during replication, parental nucleosomes are disrupted and histone proteins are released. When daughter DNA strands form, the old histones and the extra histone proteins made during S phase are put back together on the DNA. This assembly recreates nucleosomes on the new strands. The same histone marks and other epigenetic features in the DNA are also copied into the daughter genome.

Chromatin structure also affects gene expression. In most cells, much of the genome is not available to transcription factors because regulatory and coding DNA is hidden inside nucleosomes. To turn a gene on, the cell must open a local DNA region so transcription factors can bind. It must also modify histones to rearrange chromatin into a state that supports transcription.

Regulatory factor complexes help open these local chromatin regions by displacing or disrupting nucleosomes. Histone tail modifications can help keep chromatin in an active or inactive state. Some modifications reduce DNA compaction and make nucleosomes easier to destabilize or move. This gives the transcription machinery access to the DNA and helps control gene expression.

Chromatin Rebuilding During DNA Replication

chromatin-rebuilding-during-dna-replication

mitosis and cytokinesis

Mitosis and Cytokinesis Stages

Mitosis and cytokinesis are the two main steps of cell division. Mitosis is the process that divides the nucleus, while cytokinesis splits the rest of the cell. During mitosis, the cell’s genetic material is separated into two sets. This helps form two new nuclei with the same genetic information. Cytokinesis then completes division by separating the cytoplasm, which creates two daughter cells. These stages work together to make cell division possible in growing and repairing tissues.

duplication of chromatin structure

Chromatin rebuilding during DNA replication helps cells copy DNA and pass on chromosome structure to daughter cells. During cell division, the genome must be disrupted and then reassembled across the whole chromosome. This process allows chromatin to be inherited, rebuilt, and maintained in new cells. The basic unit of chromatin is the nucleosome. A nucleosome contains DNA wrapped around an octamer of histone proteins, with short linker DNA between neighboring nucleosomes. The histone proteins...

cohesins

Cohesins in Meiosis and Genetic Disorders

Cohesin protein complexes act like molecular glue that keeps sister chromatids together. They are important in both mitosis and meiosis. In mitosis, cohesin complexes are removed from chromosomes before anaphase begins. Meiosis has two rounds of chromosome separation. Meiosis I separates homologous chromosomes, while Meiosis II separates sister chromatids. This process produces four daughter cells. The Meiosis I cohesin complex is made of four subunits: Smc1, Smc3, Rec8, and Scc3. Rec8...

condensins

How Condensins Shape Mitotic Chromosomes

Condensins shape chromosomes during mitosis, the stage when a cell divides. These large protein complexes use ATP, the cell’s energy molecule, to help turn loose post-interphase DNA into compact, separate chromosomes. They organize and segregate chromosomal DNA so it can be passed on correctly. Plant and animal cells contain two condensin complexes: condensin I and condensin II. Each complex has five subunits. Two are SMC, or Structural Maintenance of Chromosomes, subunits. One is a kleisin...

the mitotic spindle

How the Mitotic Spindle Separates Chromosomes

The mitotic spindle is a microtubule-based structure that helps separate chromosomes during cell division. It forms in eukaryotic cells and moves sister chromatids to opposite ends of the parent cell. This leaves each new cell nucleus with the correct genetic material. A bipolar spindle has two poles, and that shape is important for chromosome segregation. In many animal cells, two centrosomes are present when mitosis begins. Each centrosome helps organize a circular set of microtubules at one...

centrosome duplication

Centrosome Duplication in the Cell Cycle

Centrosome duplication is a key part of the animal cell cycle. The centrosome is the main microtubule organizing center, or MTOC, in animal cells. It contains two cylindrical centrioles at its core. Each centriole has nine sets of three microtubules held together by proteins. The two centrioles sit at right angles and are surrounded by the pericentriolar matrix, or PCM, a shapeless protein cloud. Duplication starts early in the cell cycle so each daughter cell can receive a centrosome after...

microtubule instability

Microtubule Growth and Shrinkage

Microtubules are hollow, cylindrical filaments in the cell. They are about 25 nm wide and can range from 200 nm to 25 μm in length. Their main building blocks are GTP-bound tubulin subunits that form αβ-heterodimers, which then assemble into protofilaments. These protofilaments join by lateral bonds to create stable microtubule cylinders. Microtubules are highly dynamic because they repeatedly assemble and break down. They can even grow on one end while shrinking on the other at the same time.

spindle assembly

How the Mitotic Spindle Forms

The mitotic spindle forms through centrosome-mediated, chromatin-mediated, and microtubule-mediated pathways. These pathways often work at the same time. Together, they build a strong spindle apparatus for cell division. In most cells, centrosomes are the main sites where microtubules begin to grow. During the G2 to prophase transition, centrosomes mature and make more microtubules. The growing microtubules extend from both centrosomes, and their plus-ends search for chromosomes by attaching...

attachment of sister chromatids

Kinetochore-Microtubule Binding in Mitosis

Kinetochore-microtubule binding helps chromosomes line up and separate during mitosis. After the nuclear envelope breaks down, condensed chromosomes are exposed to the bipolar microtubules of the mitotic spindle. The kinetochore is a large, disc-shaped protein complex at the centromere region of each sister chromatid, and it serves as the microtubule binding site. Usually, the plus-end of a single microtubule inserts into the kinetochore. In some cases, a kinetochore first makes lateral...

forces acting on chromosomes

Chromosome Movement During Mitosis

Chromosome movement during mitosis depends on several small forces that act at different times and positions in the cell. In prometaphase, these forces help chromosomes move to the equatorial plane and line up at the metaphase plate. Because the forces change with location and stage, chromosome behavior also changes as mitosis continues. Microtubules and motor proteins create two main kinds of force on chromosomes: poleward force and anti-poleward force, also called polar-ejection force.

separation of sister chromatids

Anaphase Start and Chromatid Release

Anaphase starts when sister chromatids are released from one another and pulled toward opposite spindle poles. Before that happens, cohesion along the chromosomal arms is reduced from prophase to metaphase, which helps the sister chromatids resolve. A residual cohesin link still holds them together until the metaphase-to-anaphase transition. This leftover connection helps prevent early separation and reduces the risk of aneuploidy, or the wrong number of chromosomes, in daughter cells. At the...

the spindle assembly checkpoint

How Cells Safeguard Chromosome Separation

The spindle assembly checkpoint helps cells safeguard chromosome separation during anaphase. It acts as a molecular surveillance system. The checkpoint checks whether the steps needed for chromosome segregation are complete before the cell moves on. Many proteins work together to control this checkpoint. If mutations affect these proteins, a cell may enter anaphase too early. Chromosomes can then separate before the needed steps are finished. When this happens, the daughter cells may receive...

anaphase a and b

Chromatid Movement by Microtubule Forces

Chromatid movement during anaphase depends on microtubule forces at the spindle. Kinetochore microtubules grow from the spindle poles, and their plus ends attach to kinetochores on sister chromatids. The kinetochore protein complex Ndc80 makes low-affinity links with the microtubule plus end.

the contractile ring

How Cells Build the Contractile Ring

Contractile rings are built from microfilaments and help separate daughter cells during cytokinesis. This ring forms as the cell cycle moves forward, but the exact timing and coordination with other cell cycle events are still not fully understood. RhoA, a small GTPase in the Ras superfamily, controls contractile ring assembly and function. The inactive form of RhoA is bound to GDP. A guanine nucleotide exchange factor, or Rho-GEF, is located in the cortex region, where the next cell division...

determining the plane of cell division

How Cells Set the Division Plane

How cells set the division plane during cell division affects daughter cell size and, in many cases, cell fate. The plane of division is perpendicular to the plane of chromosome segregation. Different organisms use different cues to place it, based on their shape and needs. In animal cells, the cleavage furrow forms along the division plane from the cell cortex, the area just below the plasma membrane. The mitotic spindle is the main guide for this position. If the spindle axis changes, the...

the phragmoplast

How Plant Cells Build a New Wall

Plant cells build a new wall during cytokinesis with help from the phragmoplast. This plant structure forms from the central spindle and related cell parts as the cell finishes dividing. In animal cells, the comparable structure is the midbody, but in plants the phragmoplast expands outward to guide new wall formation. The mature phragmoplast has a donut-like shape. It has an outer leading region, a middle transition zone, and an inner lagging region. New microtubules are assembled...

distribution of cytoplasmic content

How Organelles Are Split During Cytokinesis

Cytokinesis splits a cell’s chromosomes and organelles into two daughter cells. Before cell division, organelles grow and divide. They cannot be made from scratch, so each daughter cell must inherit at least one copy to survive. Many details of this organelle sorting process are still not fully known. The cytoplasm contains organelles, salts, proteins, and water. Small organelles such as peroxisomes and lysosomes can be shared by simple diffusion. Because cells contain many copies of these...

anaphase promoting complex

APC Activates Chromosome Separation

The anaphase-promoting complex, or APC, helps control cell cycle progression by destroying specific proteins at the right time. These proteins are tagged with ubiquitin by ubiquitin ligases and then broken down by the proteasome. The SCF (Skp1/Cullin/F-box) complex and APC are two major ubiquitin ligases involved in this process. SCF stays active throughout the cell cycle, but APC turns on during the metaphase-to-anaphase transition. APC becomes active when Cdc20 or Cdh1 binds to it. These...

key terms and concepts

Explore how chromatin is broken apart and rebuilt during DNA replication, how histones are reused, and how chromatin changes affect gene expression in cells.

Chromatin Rebuilding During DNA Replication | JoVE K12

molecular biology

JoVE Core 분자생물학은 명확하고 간결한 애니메이션을 통해 분자 단계에서 일어나는 세포 과정을 설명합니다.또한, 과학자가 직접 실험을 진행하는 실사 영상을 통해 분자생물학 개념의 응용 사례를 보여줍니다.

Chromatin Rebuilding During DNA Replication

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