DNA Packaging and Eukaryotic Organization

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Questions and Answers

Which basic amino acids are primarily found in positively charged proteins that interact with DNA?

Arginine, Histidine, Lysine (correct)

Glycine, Serine, Glutamic acid

Alanine, Proline, Valine

Cysteine, Methionine, Tyrosine

Which of the following proteins is NOT one of the five types of histones?

H5 (correct)

H2A

What is the simplest unit of DNA-protein interaction in chromatin?

Chromosome

Nucleosome (correct)

Chromatid

Chromatin fiber

What is the approximate diameter of a nucleosome?

11 nm Signup and view all the answers

What structure connects nucleosomes together and is associated with H1 histone?

Linker DNA Signup and view all the answers

What is the main function of nucleosomes in DNA packaging?

Protect DNA from digestion Signup and view all the answers

Which level of eukaryotic DNA organization corresponds to the 30-nm chromatin fiber?

Heterochromatin Signup and view all the answers

What is the packing ratio associated with the 10-nm chromatin fiber?

10 folds Signup and view all the answers

What is the primary function of DNA packaging in eukaryotic cells?

To fit large amounts of DNA into chromosomes. Signup and view all the answers

What is the total number of genes in mammals approximately?

100,000 Signup and view all the answers

What is euchromatin characterized by?

Less dense and accessible for gene expression. Signup and view all the answers

What is the packing ratio of the 30-nm chromatin fiber?

8000 fold Signup and view all the answers

What is the average size of a human gene in base pairs?

3,000 bp Signup and view all the answers

During which phase of mitosis does DNA packaging primarily take place?

Prophase Signup and view all the answers

How many nucleosomes are present in each turn of the 30-nm fibril?

6-7 Signup and view all the answers

Which type of proteins support the 700-nm chromatid structure?

Non-histone proteins Signup and view all the answers

What is heterochromatin primarily associated with?

Limited gene expression. Signup and view all the answers

What is the diameter of the human cell nucleus?

6 μm Signup and view all the answers

What structural feature characterizes the ends of each chromatid?

Telomeres Signup and view all the answers

What is the ploidy of somatic cells?

Diploid Signup and view all the answers

What does the term 'blueprint of life' refer to?

DNA Signup and view all the answers

What role do anti-histone antibodies play in systemic lupus erythematosus?

They target the histone complex. Signup and view all the answers

What is the structure formed when every 6 loops of the 30-nm fiber are wrapped?

Scaffold rosettes Signup and view all the answers

What is the distinguishing feature of germ cells compared to somatic cells?

Germ cells are haploid. Signup and view all the answers

What is the primary function of the H1 histone in the 30-nm chromatin fiber?

To stabilize the supercoiling of chromatin Signup and view all the answers

How are chromosomes numbered according to their structure?

According to size and centromere position Signup and view all the answers

What unique feature do telomeres possess?

They consist of repetitive DNA sequences Signup and view all the answers

In the context of chromatid structure, what forms the 'arms' of the chromosome?

The regions p and q Signup and view all the answers

What defines the diploid genome found in somatic cells?

Presence of two sets of chromosomes Signup and view all the answers

What role do anti-histone antibodies play in the context of autoimmune diseases?

They target histone protein complexes Signup and view all the answers

What is the significance of the 700-nm chromatid structure?

It is formed by rosettes of non-histone proteins Signup and view all the answers

In systemic lupus erythematosus, the presence of anti-histone antibodies indicates a target towards what?

Histone protein complexes Signup and view all the answers

What provides the primary interaction between nucleosomes and DNA?

Ionic bonds between positively charged amino acids and negatively charged phosphates Signup and view all the answers

Which of the following statements accurately describes the structure of a nucleosome?

Wraps 146 base pairs of DNA around an octamer of histones Signup and view all the answers

What is the primary purpose of linker DNA in nucleosomes?

To aid in compaction of nucleosomes into higher-order structures Signup and view all the answers

What distinguishes euchromatin from heterochromatin?

Euchromatin is transcriptionally active Signup and view all the answers

Which feature is characteristic of the 30-nm chromatin fiber?

Represents the highest level of DNA packaging Signup and view all the answers

What is the function of the H1 histone protein in nucleosomes?

Links nucleosomes together Signup and view all the answers

What is the packing ratio associated with nucleosomes?

10 folds Signup and view all the answers

Which types of proteins are included in the basic structural unit known as a nucleosome?

Histone proteins only Signup and view all the answers

What is the primary reason for DNA packaging in eukaryotic cells?

To fit the DNA into the limited space of the nucleus Signup and view all the answers

Which type of chromatin is typically associated with active gene expression?

Euchromatin Signup and view all the answers

During which specific phase of mitosis does DNA packaging occur the most?

Prophase Signup and view all the answers

What is the average length of a human gene in base pairs?

3000 bp Signup and view all the answers

What is the total estimated number of genes found in mammals?

More than 100,000 Signup and view all the answers

What is heterochromatin primarily characterized by?

Tightly packed DNA with limited gene expression Signup and view all the answers

What is the approximate total length of DNA in all human cells?

1.8 meters Signup and view all the answers

Which part of the DNA is involved in tightly packaging DNA into chromosomes?

Histones Signup and view all the answers

What molecular structure is formed when DNA is packaged around histone proteins?

Nucleosomes. Signup and view all the answers

What type of chromatin is known for being actively engaged in gene expression?

Euchromatin. Signup and view all the answers

During which specific stage of the cell cycle does DNA packaging primarily occur?

Prophase of mitosis. Signup and view all the answers

What is the term used to describe the tightly packed form of DNA that is largely inactive in gene expression?

Heterochromatin. Signup and view all the answers

How long is the total length of DNA in all human cells?

Approximately 1.8 meters. Signup and view all the answers

What is the average size of human genes, in base pairs?

About 3000 base pairs. Signup and view all the answers

What are the main components that make up the structural units of chromosomes?

DNA and associated proteins. Signup and view all the answers

What role do histones play in the packaging of DNA?

Histones assist in tightly packaging DNA into nucleosomes. Signup and view all the answers

How do positively charged proteins interact with the negatively charged phosphate groups of DNA?

They form ionic bonds due to the attraction between opposite charges. Signup and view all the answers

What is the composition of the octamer core of a nucleosome?

It is composed of two molecules each of H2A, H2B, H3, and H4 histones. Signup and view all the answers

Explain the significance of linker DNA in the formation of chromatin.

Linker DNA connects nucleosomes and facilitates their packaging into more compact structures. Signup and view all the answers

Describe the packing ratio associated with the overall structure of chromatin.

The 30-nm chromatin fiber exhibits a packing ratio of 50-fold. Signup and view all the answers

What role do non-histone proteins play in DNA packaging?

Non-histone proteins assist in DNA replication, transcription, and regulatory functions. Signup and view all the answers

How does the 'beads-on-a-string' model of chromatin contribute to our understanding of DNA structure?

It illustrates how nucleosomes are organized along the DNA, resembling beads connected by linker DNA. Signup and view all the answers

What are the primary features that distinguish euchromatin from heterochromatin?

Euchromatin is less condensed and associated with active gene expression, while heterochromatin is more condensed and transcriptionally inactive. Signup and view all the answers

In what way does the function of H1 histone differ from the core histones?

H1 histone is involved in the higher order structure of chromatin, whereas core histones primarily form the nucleosome structure. Signup and view all the answers

What structural modification occurs during the transition from chromatin to a 700-nm chromatid?

Six loops of the 30-nm fiber are wrapped around a supporting matrix of non-histone proteins. Signup and view all the answers

Describe the role of telomeres at the ends of each chromatid.

Telomeres consist of tandem repeats of the sequence 5'-TTAGGG-3' and protect the chromosome from degradation. Signup and view all the answers

How does the presence of anti-histone antibodies relate to systemic lupus erythematosus?

Anti-histone antibodies target histone proteins, indicating an autoimmune response underlying the disease. Signup and view all the answers

What determines the classification of somatic cells compared to germ cells?

Somatic cells have a diploid genome with 23 pairs of chromosomes, while germ cells are haploid with 23 single chromosomes. Signup and view all the answers

What is the significance of the AT-rich region in chromosomal structure?

The AT-rich region binds proteins to form the kinetochore, crucial for mitotic spindle attachment during cell division. Signup and view all the answers

Describe the packing ratio change from chromatin to chromosomes.

The packing ratio increases from 8000-fold in the 30-nm fiber to 10000-fold in the 700-nm chromatid structure. Signup and view all the answers

What is the role of H1 histones in the 30-nm chromatin fiber?

H1 histones stabilize the 30-nm chromatin fiber by binding to the linker DNA between nucleosomes. Signup and view all the answers

Explain how the structure of chromosomes is classified based on the position of the centromere.

Chromosomes are numbered according to their length and the position of the centromere, which can be metacentric or acrocentric. Signup and view all the answers

What are the five types of histones involved in DNA packaging?

H1, H2A, H2B, H3, and H4. Signup and view all the answers

How does linker DNA contribute to the structure of nucleosomes?

Linker DNA connects nucleosomes together and is associated with the H1 histone. Signup and view all the answers

What is the primary role of non-histone proteins in DNA packaging?

Non-histone proteins function as enzymes for DNA packaging, replication, and transcription. Signup and view all the answers

Describe the general structure of a nucleosome.

A nucleosome consists of an octamer of histone proteins with 146 base pairs of DNA wrapped around it. Signup and view all the answers

What is the packing ratio associated with nucleosomes?

The packing ratio of nucleosomes is approximately 10 folds. Signup and view all the answers

What distinguishes euchromatin from heterochromatin?

Euchromatin is less densely packed and is actively engaged in gene expression, whereas heterochromatin is more condensed and typically inactive. Signup and view all the answers

What is the diameter of a nucleosome and how does it relate to chromatin structure?

A nucleosome has a diameter of approximately 11 nm, contributing to the overall compactness of chromatin structure. Signup and view all the answers

Explain the concept of packing ratios in DNA organization.

Packing ratios refer to the degree of DNA compaction, with nucleosomes providing a 10-fold increase and 30-nm fibers providing a 50-fold increase. Signup and view all the answers

What is the total length of DNA in all human cells?

1.8 meters Signup and view all the answers

During which stage of mitosis does DNA packaging mainly occur?

Prophase Signup and view all the answers

What distinguishes euchromatin from heterochromatin?

Euchromatin is less densely packed and available for gene expression, while heterochromatin is more tightly packed and has limited gene expression. Signup and view all the answers

What is the average size of a human gene in base pairs?

Approximately 3000 base pairs Signup and view all the answers

What is the function of histones in DNA packaging?

Histones help to tightly package DNA by wrapping it around themselves to form nucleosomes. Signup and view all the answers

How many genes are estimated to exist in mammals?

More than 100,000 genes Signup and view all the answers

What is the significance of the 30-nm chromatin fiber in DNA organization?

The 30-nm chromatin fiber represents a higher level of DNA packing, crucial for efficient chromosome formation. Signup and view all the answers

What role does DNA packaging play in the function of eukaryotic cells?

DNA packaging allows a large amount of genetic material to fit into the nucleus while remaining functional. Signup and view all the answers

What is the relationship between the 30-nm chromatin fiber and the formation of the 700-nm chromatid structure?

The 30-nm chromatin fiber supercoils into 700-nm structures by forming loops that wrap around a supporting matrix of scaffold non-histone proteins. Signup and view all the answers

What is the role of telomeres in chromosome structure?

Telomeres consist of tandem repeats of the sequence 5'-TTAGGG-3' and protect the ends of chromatids from degradation. Signup and view all the answers

How does the packing ratio of chromatin fibers change from the 30-nm to the 700-nm structure?

The packing ratio increases from 8000-fold in the 30-nm fiber to 10000-fold in the 700-nm chromatid structure. Signup and view all the answers

What clinical significance does the presence of anti-histone antibodies have in patients?

The presence of anti-histone antibodies is indicative of autoimmune conditions, such as systemic lupus erythematosus. Signup and view all the answers

What are the defining differences between somatic and germ cells in terms of chromosome number?

Somatic cells are diploid with 23 pairs of chromosomes, while germ cells are haploid containing only 23 chromosomes. Signup and view all the answers

Describe the structural composition of a nucleosome.

A nucleosome consists of a segment of DNA wrapped around a core of histone proteins, which helps compact the DNA. Signup and view all the answers

What is the significance of the 1400-nm chromosome structure in cell division?

The 1400-nm structure represents the fully condensed form of chromosomes that are identifiable during prophase. Signup and view all the answers

Explain how H1 histones contribute to chromatin stability.

H1 histones stabilize the 30-nm chromatin fiber and facilitate higher-order folding into looped structures. Signup and view all the answers

Positively charged proteins have a high content of basic amino acids like Arginine, Histidine, and __________.

Lysine Signup and view all the answers

The basic structural units of DNA packaging are called __________.

nucleosomes Signup and view all the answers

The __________ chromatin is typically associated with active gene expression.

euchromatin Signup and view all the answers

Each nucleosome consists of an octamer of core proteins, containing two molecules of each histone type: H2A, H2B, H3, and __________.

H4 Signup and view all the answers

Nucleosomes are connected by small pieces of DNA known as __________.

linker DNA Signup and view all the answers

The secondary level of DNA organization in eukaryotes is the __________ chromatin fibril.

10-nm Signup and view all the answers

The packing ratio of nucleosomes allows packaging of DNA into a __________-fold more compact structure.

50 Signup and view all the answers

The simplest unit of DNA packaging is referred to as the __________.

bead-on-a-string Signup and view all the answers

The hereditary material of the cell is called ______.

DNA Signup and view all the answers

Eukaryotic cells store their DNA in structures known as ______.

chromosomes Signup and view all the answers

The average size of a human gene is approximately ______ base pairs.

3000 Signup and view all the answers

The 30-nm chromatin fiber is stabilized by ______ histones.

H1 Signup and view all the answers

Each chromosome is formed of 2 identical sister ______ connected at the centromere.

chromatids Signup and view all the answers

During prophase of mitosis, DNA is tightly packaged into ______.

chromosomes Signup and view all the answers

The ends of each chromatid consist of tandem repeats of ______ sequences called telomeres.

TTAGGG Signup and view all the answers

Histones are proteins around which DNA is ______ to form nucleosomes.

wrapped Signup and view all the answers

Somatic cells have a ______ genome, while germ cells have a haploid genome.

diploid Signup and view all the answers

Euchromatin is characterized by being ______ packed, allowing for gene expression.

less densely Signup and view all the answers

Heterochromatin is known for being ______ packed, often limiting gene expression.

more tightly Signup and view all the answers

The supercoiling of the 30-nm fibril into twisted-looped structures gives rise to ______-nm chromatid.

700 Signup and view all the answers

Anti-histone antibodies may target the ______ complex or any of the protein subunits.

histone Signup and view all the answers

The total length of DNA in all human cells is approximately ______ meters.

1.8 Signup and view all the answers

Each 30 rosettes form 1 turn of a coil that forms each ______.

chromatid Signup and view all the answers

Chromosomes are numbered according to length and position of ______.

centromere Signup and view all the answers

Study Notes

DNA Packaging

Positively charged proteins bind to negatively charged phosphate groups on DNA
These proteins are called histones and have a high content of basic amino acids like Arginine, Histidine, and Lysine
There are five types of histones: H1, H2A, H2B, H3, and H4
Histones form nucleosomes, the basic structural units of DNA packaging

Non-histone Proteins

These proteins are involved in DNA packaging, replication, and transcription
Non-histone proteins include structural proteins, enzymes, and regulatory factors

Levels of Eukaryotic DNA Organization

Nucleosomes are the simplest unit of DNA-protein interaction
A 10-nm chromatin fibril is formed by packing nucleosomes together
A 30-nm chromatin fiber is formed by supercoiling the 10-nm chromatin fibril
A 700-nm chromatid is formed by supercoiling the 30-nm chromatin fiber
A 1400-nm chromosome is formed by two identical sister chromatids connected at the centromere

Nucleosome Structure

Nucleosomes consist of a core of eight histone proteins (two molecules each of H2A, H2B, H3, and H4)
DNA is wrapped around the core histone proteins in 1.75 turns (146 base pairs)
Linker DNA (50 bp long) connects nucleosomes and is associated with the H1 histone
Nucleosomes are 11nm in diameter and 5 nm high

Nucleosome Function

Protects DNA from digestion by nucleases
Provides a 10-fold packing ratio

10-nm Chromatin Fibril

Linker DNA and H1 facilitate packing of nucleosomes into a more compact structure
Provides a 50-fold packing ratio

30-nm Chromatin Fiber

Supercoiled 11-nm fibril with 6-7 nucleosomes per turn
Stabilized by H1 histones
Provides an 8000-fold packing ratio

700-nm Chromatid

Supercoiled 30-nm fibril into twisted-looped structures
Every 6 loops are wrapped around a supporting matrix of scaffold non-histone proteins rosettes
Each 30 rosettes form 1 turn of a coil that forms each chromatid
Provides a 10000-fold packing ratio

1400-nm Chromosome

Each chromosome is formed of two identical sister chromatids connected at the centromere
Chromosomes are numbered according to their length and position of the centromere

Centromere

An AT-rich region (up to 106 bp long)
Binds certain proteins to form the kinetochore, which binds to the mitotic spindle
Forms the "arms" of the chromosome: p (shorter arm) and q (longer arm)

Telomeres

The ends of each chromatid consist of tandem repeats of (5’-TTAGGG-3’ sequences)
Telomeres are many kilobase pairs long
Become shorter with aging and cancer

Chromosome Number

Somatic cells (any cell not part of the germline) are diploid, meaning they have 23 pairs of chromosomes
Germ cells (gametes like sperm or ovum) are haploid, meaning they have 23 chromosomes only

Systemic Lupus Erythematosus (SLE)

SLE is an autoimmune disease characterized by inflammation of various organs and tissues
Facial butterfly rash, polyarthritis, and general malaise are classic symptoms
Anti-histone antibodies are commonly found in SLE patients
These antibodies can target the histone complex or any of the protein subunits

DNA Packaging

Positively charged proteins bind to negatively charged phosphate groups of DNA.
Five types of histone proteins: H1, H2A, H2B, H3, and H4.
Histone proteins form nucleosomes, the basic structural unit of chromatin.
Non-histone proteins: structural proteins for DNA packaging, enzymes for replication and transcription, and regulatory factors for replication and transcription.

Levels of DNA Organization

Nucleosomes: beads-on-a-string structure, contain an octamer of histone proteins, 146 base pairs of DNA wrapped around the octamer, connected by linker DNA with H1 histone associated.
10-nm chromatin fibril is formed by the packing of nucleosomes.
30-nm chromatin fiber is formed by the supercoiling of the 10-nm chromatin fibril.
700-nm chromatid is formed by the supercoiling of the 30-nm chromatin fiber.
1400-nm chromosome is formed by the packaging of two sister chromatids connected at the centromere.

DNA Packaging Ratios

Nucleosome packing ratio: 10 fold
10-nm chromatin fibril packing ratio: 50 fold
30-nm chromatin fiber packing ratio: 8000 fold
700-nm chromatid packing ratio: 10000 fold

Chromosomes

Centromere: AT-rich region, binds proteins to form kinetochore, defines the "arms" of the chromosome (p - shorter, q - longer).
Telomere: tandem repeats of the 5'-TTAGGG-3' sequence located at the ends of each chromatid, shorten with aging and cancer.

DNA Function and Diversity

DNA is the hereditary material of the cell, the blueprint of life.
Chromosomes are molecules of DNA.
Genes are functional units of DNA on chromosomes that code for specific traits.
The number of genes in mammals is over 100,000.
The average size of human genes is 3000 base pairs, with the largest being 2.4 million base pairs.

Clinical Correlates

Anti-histone antibodies are found in patients with systemic lupus erythematosus. These antibodies target the histone complex or its protein subunits.

DNA Packaging

Positively charged proteins bind to negatively charged DNA
Histone proteins are basic structural units called nucleosomes
Five types of histone proteins: H1, H2A, H2B, H3, H4
Non-histone proteins include: structural proteins, enzymes, and regulatory factors
Levels of eukaryotic DNA organization:
- Nucleosomes
- 10-nm chromatin fibril
- 30-nm chromatin fiber
- 700-nm chromatid
- 1400-nm chromosome

Nucleosomes

Simplest unit of DNA-protein interaction
Disc-core proteins called octamer
1.75 turns of DNA double helix (146 base pairs) are wrapped around the core
Connected by small pieces of DNA called linker DNA, to which H1 histone is associated
Protect DNA from nuclease digestion
Packing ratio: 10 folds

10-nm Chromatin Fibril

Facilitated by linker DNA and H1 histones to pack into a more compact structure
Packing ratio 50 folds
Highly coiled and complex structure

30-nm Chromatin Fiber

Supercoiling of 11 nm fibril with 6-7 nucleosomes per turn
Stabilized by H1
Packing ratio: 8000 folds

700-nm Chromatid

Supercoiling of 30 nm fibril into twisted-looped structure
6 loops are wrapped around a supporting matrix of scaffolding non-histone proteins
30 rosettes form 1 turn of a coil
Packing ratio: 10000 folds

1400-nm Chromosome

Formed from 2 identical sister chromatids connected at the centromere
Numbered by length and the position of the centromere

Centromere

AT-rich region up to 106 bp long
Binds proteins to form kinetochore
Forms the "arms" of the chromosomes:
- p: shorter
- q: longer

Telomere

Consists of tandem repeats of 5'-TTAGGG-3' sequences
Become shorter with aging and cancer

Genetic diversity

DNA is the blueprint of life
The different arrangements of nucleotides in nucleic acids provide the key to diversity among living organisms

Human cells

The total length of DNA in a human cell is 1.8 meters
Nucleus diameter is 6 micrometers
Tight DNA packaging is required to fit in the nucleus

DNA packaging: Key facts

The site of DNA packaging is the nucleus of eukaryotic cells.
The process occurs during prophase of mitosis, prior to cell division.

Euchromatin and Heterochromatin

Euchromatin:
- Less densely packed DNA
- Active for gene expression
Heterochromatin:
- More tightly packed DNA
- Areas of limited gene expression

Gene definition

Units of genetic material that code for a specific trait
DNA sequence that encodes a protein or a character

Genes: Key facts

More than 100,000 genes in a mammal
Humans: average size = 3000 bp; largest = 2.4 million bp

Clinical Correlates

Lupus Erythematosus is a chronic autoimmune disease.
The presence of anti-histone antibodies may target the histone complex or specific protein subunits.

DNA Packaging

Positively charged proteins bind to the negatively charged phosphate group of DNA through ionic bonds.
These proteins are called histones and are responsible for packaging DNA into chromatin.
There are five main types of histones: H1, H2A, H2B, H3, and H4.
Histones form nucleosomes, the basic structural units of chromatin.

Nucleosomes

A nucleosome consists of an octamer of histone proteins (two molecules each of H2A, H2B, H3, and H4) around which 1.75 turns of DNA double helix (146 base pairs) are wrapped.
Linker DNA, a short segment of DNA (50 bp long), connects adjacent nucleosomes and is associated with the H1 histone.
This structure protects DNA from nuclease digestion and results in a 10-fold packing ratio.

Levels of Eukaryotic DNA Organization

The 10-nm chromatin fibril is formed by the packing of nucleosomes.
The 30-nm chromatin fiber is formed by the supercoiling of the 10-nm fibril.
The 700-nm chromatid is formed by the supercoiling of the 30-nm fiber into twisted-looped structures.
The 1400-nm chromosome is formed by the association of two identical sister chromatids at the centromere.

Euchromatin vs. Heterochromatin

Euchromatin is less densely packed DNA and is associated with active genes.
Heterochromatin is more tightly packed DNA and is associated with areas of limited gene expression.

Centromere

The centromere is an AT-rich region (up to 106 bp long) that binds certain proteins to form the kinetochore.
The kinetochore attaches to the mitotic spindle, which is responsible for separating chromosomes during cell division.

Telomeres

Telomeres are tandem repeats of the 5'-TTAGGG-3' sequence located at the ends of each chromatid.
They protect chromosomes from degradation and contribute to their stability.
They become shorter with age and may be implicated in cancer development.

Systemic Lupus Erythematosus (SLE)

SLE is an autoimmune disease that can cause a wide range of symptoms.
One of the hallmarks of SLE is the presence of anti-histone antibodies.
These antibodies can target the histone complex or any of its individual subunits.
Anti-histone antibodies may contribute to the pathogenesis of SLE by interfering with the DNA packaging process.

DNA Packaging

Positively charged proteins bind to the negatively charged phosphate groups of DNA
Five types of Histones: H1, H2A, H2B, H3, H4
Histones are involved in packaging DNA into Chromatin
Non-histone proteins include enzymes, regulatory factors, and structural proteins involved in DNA packaging
Levels of eukaryotic DNA organization include: nucleosomes, 10-nm chromatin fibril, 30-nm chromatin fiber, 700-nm chromatid, 1400-nm chromosome

Nucleosome

Basic unit of DNA-protein interaction
Contains an octamer of proteins, with two molecules of each histone: H2A, H2B, H3, H4
1.75 turns of DNA double helix (146 base pairs) are wrapped around the histone core
Connected by linker DNA, which is bound by histone H1
Protects DNA from being degraded by nucleases
Packing ratio: 10 fold

10-nm Chromatin Fibril

Linker DNA and histone H1 facilitate the packing of nucleosomes into a more compact structure
Packing ratio: 50 fold

30-nm Chromatin Fiber

Supercoiling of the 11-nm fibril
6-7 nucleosomes per turn
Stabilized by histone H1
Packing ratio: 8,000 fold

700-nm Chromatid

Supercoiling of the 30-nm fiber into twisted, looped structures
6 loops are wrapped around a scaffold of non-histone proteins
30 rosettes form one turn of a coil that forms each chromatid
Packing ratio: 10,000 fold

1400-nm Chromosome

Consists of two identical sister chromatids connected at the centromere
Numbered according to length and position of centromere

Centromere

AT-rich region (up to 106 bp long)
Binds proteins to form the kinetochore, which attaches to the mitotic spindle
Forms the "arms" of chromosomes: p (shorter) and q (longer)

Telomere

Tandem repeats of 5'-TTAGGG-3' sequences
Essential for chromosome stability and replication
Becomes shorter with aging and cancer

Systemic Lupus Erythematosus (SLE)

Autoimmune disease characterized by symptoms such as facial butterfly rash, polyarthritis, and general malaise
Anti-histone antibodies are commonly found in SLE patients
These antibodies can target the histone complex or any of its individual protein subunits

Genetic Diversity

Differences in the arrangement of nucleotides in DNA provide genetic diversity.

DNA

Hereditary material of the cell
Blueprint of life

Chromosome

Molecule of DNA

Gene

Functional unit of DNA located on a chromosome
DNA sequence that codes for a specific trait
Number of genes in mammals is greater than 100,000
Average human gene size is 3,000 base pairs, with the largest being 2.4 million base pairs.

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Description

Explore the intricate mechanisms of DNA packaging in eukaryotic cells. This quiz covers the roles of histones and non-histone proteins in DNA organization, as well as the levels of DNA structure from nucleosomes to chromosomes. Test your knowledge about the structural units of DNA and their functions.