Name: how dna fits inside the nucleus
Uploaded: 2023-06-23T15:38:44.000Z
Duration: 1 min 32 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.2

LS.2.b

Chromatin Packaging

In diploid human cells, about two meters of DNA is compressed inside a nucleus with a diameter of a few microns.
DNA, along with histone proteins, forms a complex called chromatin. Under a microscope, the extended chromatin resembles beads on a string. Each bead is called a nucleosome, comprising DNA wrapped around a core of histones. Being packaged into nucleosomes shortens the DNA length sevenfold.
After binding linker histones, the nucleosomes are stacked in a helical array, creating a shorter, thicker fiber with a diameter of 30 nanometers called the 30-nanometer fiber.
The widely accepted Solenoid model proposes that nucleosomes are arranged in a left-handed helix with six or more nucleosomes per turn, shortening the DNA length by 50-fold.
This arrangement ensures actively transcribed or replicated chromatin regions occur in an extended beads-on-a-string form while the rest exist in the 30-nm fiber form.
The 30-nanometer fibers then coil, forming 300-nanometer-long loops, which are further compressed into 250-nanometer-wide coils.
During metaphase, chromatin fibers form highly condensed chromosomes. After cell division, the chromosomes uncoil again.

chromatin packaging

Each human somatic cell contains 6 billion base pairs of DNA. Each base pair is 0.34 nm long, meaning each diploid cell contains a staggering 2 meters of DNA. This long DNA strand is packed inside a nucleus measuring only 10-20 microns in diameter with the help of specialized DNA-binding proteins called histones. Together they form a compact DNA-protein complex called chromatin. The chromatin is further compacted into higher-order structures. The highest level of compaction is achieved during the cell cycle&#39;s metaphase, where the chromatin condenses to form the chromatids of a chromosome.
Nucleosomes
Nucleosomes are the basic functional and repeating unit of chromatin. A nucleosome consists of 8 histone proteins wound around by 147 base pairs of DNA. Under electron microscopy, the chromatin resembles beads on a string due to the presence of nucleosomes along its length. The packaging of DNA into nucleosomes shortens its length by sevenfold.
Solenoid model
The nucleosomes are further coiled into 30 nm fibers. Such compaction is explained by a widely accepted hypothesis - the solenoid model. A solenoid refers to the structure of a wire coiled on a central axis. This model proposes that nucleosomes are arranged in a left-handed helical conformation with six or more nucleosomes per turn. One of the non-core histone proteins, H1, plays an essential role in nucleosome compaction; in its absence, the chromatin fiber turns into irregular clumps of nucleosomes.
Compaction also makes DNA less accessible to the replication and transcription enzymes. As a result, less condensed chromatin, called euchromatin, is more accessible to transcription enzymes as compared to densely packed heterochromatin.
Chromatin packaging is an active area of research. The emerging data has allowed scientists to view chromatin and nucleosomes not as highly defined structures but as a continuum of various inter-convertible conformations at all chromatin packaging stages.
This text is adapted from <a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/">Openstax, Anatomy and Physiology 2e, Section 3.3: Nucleus and DNA replication</a> and <a href="https://openstax.org/books/biology-2e/pages/10-1-cell-division">Openstax, Biology, Section 10.1: Cell division</a>.

Each human somatic cell contains 6 billion base pairs of DNA. Each base pair is 0.34 nm long, meaning each diploid cell contains a staggering 2 meters of ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

Cells and their Components

KEY TERMS AND CONCEPTS

how dna fits inside the nucleus

Chromatin is the DNA-protein material that helps human DNA fit inside the nucleus. A human somatic cell contains about 6 billion base pairs of DNA, and each base pair is 0.34 nm long. That means a diploid cell holds about 2 meters of DNA inside a nucleus that is only 10 to 20 microns wide.

Histones make this packing possible. These specialized DNA-binding proteins help organize DNA into a compact chromatin structure. Chromatin is then folded into higher-order forms, and it reaches its highest level of compaction during metaphase, when it condenses to form the chromatids of a chromosome.

The basic repeating unit of chromatin is the nucleosome. A nucleosome contains 8 histone proteins with 147 base pairs of DNA wrapped around them. Under the electron microscope, this arrangement looks like beads on a string, and it shortens DNA length by about sevenfold.

Nucleosomes can coil even further into 30 nm fibers. This level of folding is often explained by the solenoid model, which describes a wire-like structure coiled around a central axis. In this model, nucleosomes form a left-handed helix with six or more nucleosomes per turn.

The non-core histone protein H1 helps nucleosomes compact into this tighter fiber. Without H1, the chromatin fiber becomes irregular clumps of nucleosomes. This packing also affects gene activity, because compact DNA is less available to the enzymes used in replication and transcription.

Less condensed chromatin is called euchromatin, and it is more accessible to transcription enzymes. Densely packed chromatin is called heterochromatin, and it is less accessible. Scientists now view chromatin packaging as an active research area, and current data suggest that chromatin and nucleosomes can shift through a continuum of inter-convertible conformations at different packaging stages.

How DNA Fits Inside the Nucleus

what are cells?

Cells as the Basic Unit of Life

Cells are the basic unit of life. They are the smallest structures that make up living things, and they carry out the jobs needed to stay alive. Many organisms are made of one cell, while others are made of many cells working together. Cells share a few common features, but not all cells are the same. Some cells have a nucleus, which holds the genetic material, and other cells do not. Cells also differ in size, shape, and the specific work they do in an organism. Understanding cells helps...

cell diversity

How Cells Become Specialized

Cells are the basic units of life, and they can become specialized for different jobs in the body. The idea of the cell began in 1665, when Robert Hooke looked at dead cork tissue under a microscope and named the small boxlike spaces "cells" because they reminded him of monks' rooms. About ten years later, Antonie van Leeuwenhoek became the first person to see living, moving cells under a microscope. Over the next century, scientists developed the theory that cells are the fundamental unit of...

cytoplasm

Cytoplasm: The Cell’s Internal Fluid

Cytoplasm is the internal fluid of the cell. It fills the space inside the cell membrane and surrounds the cell’s structures. This fluid helps support the cell and gives organelles a place to stay suspended. It is an important part of cell structure because many cell activities happen within it. In many cells, the cytoplasm also helps move materials around the cell. Its fluid nature allows substances to travel where they are needed and helps keep the cell organized.

the nucleus

Nucleus Structure and Cell Control

The nucleus is the cell’s control center. It helps direct how a cell works and supports the cell’s genetic material. In many eukaryotic cells, the nucleus is the most obvious internal organelle. The nucleus is surrounded by a nuclear envelope. This envelope separates the nucleus from the rest of the cell. It also helps protect the DNA inside. Inside the nucleus, the genetic material is organized as chromatin. Chromatin contains DNA and proteins. When a cell prepares to divide, this material...

the nucleosome

DNA Packing with Histones

DNA packing with histones allows human DNA to fit inside the cell nucleus. Human DNA is almost two meters long, but the nucleus is only a few microns wide. To fit this amount of DNA into such a small space, it is organized into several levels of compaction. The most compact form of DNA is the chromosome, which can be seen under a microscope in a dividing cell. Inside a chromosome, DNA wraps twice around a histone octamer core. This core is made of eight histone proteins. The DNA and histone...

the nucleosome core particle

Histone Tails and DNA Packing

Nucleosomes help pack and protect DNA inside the cell. They are made when DNA wraps around a histone core. That core is an octamer, or eight-part protein complex, with two copies each of H2A, H2B, H3, and H4. Nucleosomes must do two jobs at once. They protect fragile DNA from physical damage and help DNA fit into a smaller space. They also must let polymerase enzymes reach histone-bound DNA during replication and transcription. To solve this, the DNA can partially unfold when needed, while...

Chromatin is the DNA-protein material that helps human DNA fit inside the nucleus. A human somatic cell contains about 6 billion base pairs of DNA, and each base pair is 0.34 nm long. That means a diploid cell holds about 2 meters of DNA inside a nucleus that is only 10 to 20 microns wide. Histones make this packing possible. These specialized DNA-binding proteins help organize DNA into a compact chromatin structure. Chromatin is then folded into higher-order forms, and it reaches its highest...

the endoplasmic reticulum

Endoplasmic Reticulum: Cell Transport Network

The endoplasmic reticulum is a major membrane network inside the cell. It helps move materials and supports cell function. Its structure gives the cell a large internal surface for important processes. The endoplasmic reticulum has two main forms. Rough endoplasmic reticulum has ribosomes attached to its surface, while smooth endoplasmic reticulum does not. These forms help the cell handle different tasks. The rough endoplasmic reticulum is linked to protein production. The smooth endoplasmic...

golgi apparatus

Golgi Apparatus in Cell Transport

The Golgi apparatus is a cell structure that helps sort and move materials inside the cell. It works with membrane traffic, which is the movement of substances in small membrane-bound packages. The Golgi apparatus receives materials from other parts of the cell and processes them before they are sent to their next destination. It plays an important role in helping the cell organize what it makes and where those materials go. In many cells, the Golgi apparatus is part of a larger system of...

lysosomes

Lysosomes and Cell Recycling

Lysosomes are cell organelles that help break down worn-out materials and recycle useful parts. They contain digestive enzymes that work inside a membrane-bound compartment. This makes them important for keeping cells clean and organized. Lysosomes use hydrolytic enzymes to digest large molecules, cell debris, and other unwanted material. Their membrane helps protect the rest of the cell from these enzymes. When digestion is complete, the cell can reuse some of the released building blocks. <br...

mitochondria

Mitochondria in Cellular Energy Production

Mitochondria are cell structures linked to energy production. They help cells convert energy from nutrients into a usable form. In many cells, they are important for keeping energy supply steady. Mitochondria also have their own DNA. This sets them apart from many other parts of the cell. Their structure and genetic material help scientists study how they function in cells. Understanding mitochondria is important in biology because energy use affects how cells work. These structures play a...

mitochondrial membranes

Mitochondrial Membranes in Energy Production

Mitochondrial membranes help cells make energy. They form the outer boundary of the mitochondrion and also create the inner folds inside it. These membranes give the organelle its structure and support its role in energy production. The outer membrane surrounds the mitochondrion. The inner membrane is folded into many cristae, which increase surface area. This extra surface gives more space for the steps that help the cell produce usable energy. Together, the mitochondrial membranes separate...

peroxisomes

Peroxisome Functions in Cells

Peroxisomes are small organelles in cells that help manage chemical reactions. They are known for breaking down fatty acids and for handling harmful byproducts made during metabolism. These roles help keep the cell functioning normally. Peroxisomes also contain enzymes that use and break down hydrogen peroxide. Hydrogen peroxide is a reactive molecule, so cells must control it carefully. By processing it, peroxisomes support the cell's chemical balance. In cell biology, peroxisomes are...

ribosomes

Ribosomes and Protein Assembly

Ribosomes are the cell structures that build proteins. They read the instructions carried by messenger RNA, or mRNA, and join amino acids together in the correct order. This process is called translation. Ribosomes are made of ribosomal RNA and proteins. They work as the site where genetic information is turned into a protein. As the ribosome moves along the mRNA strand, it helps match each code in the message with the right amino acid. Protein assembly by ribosomes is a key step in how cells...

the proteasome structure

How Cells Tag Proteins for Breakdown

Cells use the ubiquitin-proteasome pathway to remove cytoplasmic proteins that are misfolded, damaged, or no longer needed. In this pathway, a protein is first tagged with ubiquitin, a small protein marker. This ubiquitination usually adds a chain of ubiquitin molecules to the 48th lysine residue on the target protein. The tag helps the proteasome tell a protein that should be removed from a healthy one. The proteasome is a large, ATP-driven protease called the 26S proteasome. It is found in...

the proteasome

How Cells Remove Damaged Proteins

Eukaryotic cells use the ubiquitin-proteasome pathway to remove damaged, misfolded, or unwanted cytoplasmic proteins. This selective cleanup helps protect the cell and keep protein levels under control. In this pathway, target proteins are tagged with ubiquitin, a small protein label. Three enzymes work together to attach ubiquitin to the target: E1, the ubiquitin-activating enzyme; E2, the ubiquitin-conjugating enzyme; and E3, the ubiquitin ligase. After tagging, the ubiquitinated proteins...

introduction to cytoskeleton

Cytoskeleton: Cell Support and Movement

The cytoskeleton gives cells shape, support, and the ability to move. It is a network of protein fibers inside the cell. These fibers help organize the cell and keep its parts in place. The cytoskeleton includes microfilaments, intermediate filaments, and microtubules. Microfilaments are made of actin. They help the cell change shape and move. Intermediate filaments provide strength. Microtubules are larger fibers that help with cell organization and transport. Together, these structures...

centrioles and centrosomes

Centrosomes in Cell Division

Centrosomes help organize cell division in animal cells. Most animal cells contain a pair of centrioles that together make a centrosome. Before division begins, the cell copies its centrosome so that two centrosomes sit side by side. During prophase, these centrosomes start moving toward opposite sides of the cell. As the centrosomes separate, microtubules grow outward from each one. These fibers and the centrosomes form the mitotic spindle. Near the end of prophase, also called prometaphase...

microtubules in cell motility

Microtubules and Cell Movement

Microtubules help cells move and change shape. They are part of the cell’s internal support system, called the cytoskeleton. In moving cells, microtubules work with other cell parts to guide motion. These structures are built from tubulin, a protein that joins together to form long, hollow tubes. Their shape makes them strong and flexible enough to support cell activity. In many cells, microtubules also help organize movement inside the cell. Cell motility means the ability of a cell to move.

mechanism of ciliary motion

How Cilia Create Movement

Cilia create movement by bending in a coordinated way. These tiny, hairlike structures help cells and fluids move in specific directions. The mechanism of ciliary motion explains how this repeated motion works. Cilia beat through a controlled motion that depends on their internal structure. Their movement is not random. It follows a set pattern that allows the cilia to push material across a surface or help a cell move. Understanding ciliary motion is important in cell biology. It shows how...

microvilli

Microvilli and Cell Surface Area

Microvilli are tiny finger-like projections on the surface of certain cells. They increase the surface area of the apical surface, which helps cells absorb or secrete substances more effectively. These structures are common in cells lining the small intestine, kidney tubules, and some cells in the respiratory and reproductive systems. Each microvillus has a core made of actin filaments. Actin is a structural protein that helps support cell shape. Other proteins, including villin and fimbrin,...

key terms and concepts

Learn how histones, nucleosomes, and chromatin help pack 2 meters of DNA into a tiny nucleus, and how DNA packing affects gene access.

How DNA Fits Inside the Nucleus | 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.

Georgia Standards of Excellence

9-12

Biology

SB1.a

Cell Structure

Background
Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, ...

What are Cells?

Cells are the smallest and basic units of life, whether it is a single cell that forms the entire organism, e.g., in a bacterium, or trillions of them, ...

Animal and Plant Cell Structure

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Cell Diversity

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An Introduction to Cell Division

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The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include the development of the cell theory demonstrates the nature of science;

LS.2.a

Cytoplasm

The Nucleus

The Nucleosome

Human DNA is almost two meters long. However, it is compressed inside a tiny nucleus measuring only a few microns in diameter. To make this degree of ...

The Nucleosome Core Particle

Nucleosomes are the DNA-histone complex, where the DNA strand is wound around the histone core. The histone core is an octamer containing two copies of ...

The Endoplasmic Reticulum

Golgi Apparatus

Lysosomes

Mitochondria

Mitochondrial Membranes

Peroxisomes

Ribosomes

Introduction to Cytoskeleton

Centrioles and Centrosomes

Most animal cells comprise a pair of centrioles together called a centrosome. The cell duplicates its centrosome and contains two centrosomes ...

Functions of Life

Human life is characterized by a variety of functions that are essential for survival and well-being. These functions include metabolism, movement, ...

Requirements for Human Life

The Earth and its atmosphere have provided humans with air, water, and food, but these are not the only requirements for survival. Humans also require a ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include cell structure and organelles support life processes;

Visualizing Onion and Cheek Cells
ExpandImmediately before the experiment, wash and peel onion bulbs for the class.
Remove the entire brown outer skin and ...

Visualizing Onion and Human Cells
ExpandIn this experiment you will prepare different types of cells from a plant and animal, onion and human ...

Prokaryotic vs. Eukaryotic Cells

Prokaryotic and eukaryotic cells represent two fundamental types of cellular organization, differing significantly in structure, complexity, and function. ...

Plant Cells and Tissues

Plant tissues are collections of similar cells performing related functions. Different plant tissues will have their own specialized roles and can be ...

Tissues

Cells with similar structure and function are grouped into tissues. A group of tissues with a specialized function is called an organ. There are four main ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include similarities and differences between plant and animal cells determine how they support life processes;

LS.2.c

Mitosis and Cytokinesis

In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome ...

What is the Cell Cycle?

The cell cycle refers to the sequence of events occurring throughout a typical cell&#x2019;s life. In eukaryotic cells, the somatic cell cycle has two ...

Binary Fission

Fission is the division of a single entity into two or more parts, which regenerate into separate entities that resemble the original. Organisms in the ...

Live Cell Imaging of Mitosis

Mitosis is a form of cell division in which a cell&#8217;s genetic material is divided equally between two daughter cells. Mitosis can be broken down into ...

The Cell Cycle Control System

The cell cycle is an organized set of events that leads the cell to divide into two daughter cells, each containing chromosomes identical to the parent ...

Cell Division

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, ...

Preparation of Onion Root Tips and Solutions
ExpandFor the cell cycle experiment using root tips, first, leave an onion suspended over a beaker of water ...

Observing the Cell Cycle in a Root Tip
ExpandHypotheses: The experimental hypothesis is that in root tips slices that have been treated with nocodazole, a ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include cell division is the mechanism for growth and reproduction; and

LS.2.d

What are Membranes?

A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved semi-permeable ...

Membrane Fluidity

Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are ...

Fluid Mosaic Model

The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of ...

What is an Electrochemical Gradient?

Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient of an ...

Diffusion

Diffusion is the passive movement of substances down their concentration gradients&#x2014;requiring no expenditure of cellular energy. Substances, such as ...

Osmosis

Approximately 60% to 95% of the weight of living organisms is attributed to water. Therefore, maintaining appropriate water balance within cells is of ...

Tonicity in Animals

The tonicity of a solution determines if a cell gains or loses water in that solution. The tonicity depends on the permeability of the cell membrane for ...

Tonicity in Plants

Tonicity describes the capacity of a cell to lose or gain water. It depends on the quantity of solute that does not penetrate the membrane. Tonicity ...

Introduction to Membrane Proteins

The cell membrane, or plasma membrane, is an ever-changing landscape. It is described as a fluid mosaic where various macromolecules are embedded in the ...

Facilitated Transport

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and ...

Primary Active Transport

In contrast to passive transport, active transport involves a substance being moved through membranes in a direction against its concentration or ...

Secondary Active Transport

One example of how cells use the energy contained in electrochemical gradients is demonstrated by glucose transport into cells. The ion vital to this ...

Receptor-mediated Endocytosis

Overview

Receptor-mediated endocytosis is a process through which bulk amounts of specific molecules can be imported into a cell after binding to cell ...

Pinocytosis

Cells use energy-requiring bulk transport mechanisms to transfer large particles, or large amounts of small particles, into or out of the cell. The cells ...

Phagocytosis

Cells pull particles inward and engulf them in spherical vesicles in an energy-requiring process called endocytosis. Phagocytosis (&#x201C;cellular ...

Exocytosis

Exocytosis is used to release material from cells. Like other bulk transport mechanisms, exocytosis requires energy.

While endocytosis takes particles ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include cellular transport (osmosis and diffusion) is important for life processes.

LS.2.e

How DNA Fits Inside the Nucleus

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