DNA Packaging and Chromatin Architecture

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Questions and Answers

What is the fundamental unit of chromatin?

Chromatin fiber

DNA linker

Histone octamer

Nucleosome core particle (NCP) (correct)

Which of the following is NOT a core histone?

H2A

H1 (correct)

H2B

What is the histone fold?

A region of the histone that interacts with the DNA linker

A specific DNA sequence that binds to histones

A structural motif that allows histones to bind to each other (correct)

A type of protein that modifies histone tails

How many minor grooves of the DNA are facing towards the histone octamer in the nucleosome core particle?

12 (A) Signup and view all the answers

What is the function of the DNA linker?

To connect adjacent nucleosomes (D) Signup and view all the answers

What is the function of linker histone H1?

To bind to the DNA linker and help compact chromatin (A) Signup and view all the answers

What is the difference between euchromatin and heterochromatin?

Euchromatin is less condensed than heterochromatin and is actively transcribed. (D) Signup and view all the answers

What is the term for the arrangement of the histone octamer?

Tripartite arrangement (A) Signup and view all the answers

What type of heterochromatin is associated with inactive genes and is not a permanent characteristic of every cell's nucleus?

Facultative heterochromatin (C) Signup and view all the answers

Which type of chromatin is characterized by dense packing and protects DNA from endonuclease damage?

Constitutive heterochromatin (A) Signup and view all the answers

Which feature distinguishes euchromatin from heterochromatin?

Euchromatin is rich in gene concentration. (A) Signup and view all the answers

What percentage of the entire human genome is estimated to be composed of euchromatin?

90% (A) Signup and view all the answers

What is the primary function of euchromatin during the transcription process?

To allow DNA to be readily available for transcription (D) Signup and view all the answers

How does euchromatin participate in gene regulation?

By transforming into heterochromatin (B) Signup and view all the answers

What role does histone methylation play in facultative heterochromatin?

It silences genes, making them inactive. (B) Signup and view all the answers

Which cellular component aids in making euchromatin more accessible during transcription?

Histones (B) Signup and view all the answers

What is the role of histone chaperones during DNA processes?

They assist in chromatin assembly and disassembly. (A) Signup and view all the answers

Which model describes a packing density of 11 nucleosomes?

One-start helix model (C) Signup and view all the answers

Why is heterochromatin considered inaccessible to gene expression proteins?

It is tightly packed and highly condensed. (D) Signup and view all the answers

What distinguishes the two-start helix model from the one-start helix model?

The two-start model has a zigzag stacking of nucleosomes. (B) Signup and view all the answers

Which of the following is a common characteristic of heterochromatin?

Intense staining with DNA-specific stains. (C) Signup and view all the answers

What is the primary determinant for the need of different compaction in DNA?

The accessibility required for transcription. (D) Signup and view all the answers

What is nucleoplasmin known for?

It is the first isolated histone chaperone. (B) Signup and view all the answers

What type of interactions occur between positively charged regions and the phosphate backbone in nucleosomes?

Attractive interactions. (D) Signup and view all the answers

Study Notes

DNA Packaging & Chromatin Architecture

DNA is packaged into a highly organized structure called chromatin
This packaging allows the vast amount of DNA to fit within the nucleus of a cell
The fundamental unit of chromatin is the nucleosome
Nucleosomes consist of a core of histone proteins around which DNA is wrapped
The nucleosome core particle (NCP) contains the histone octamer and 147 base pairs of DNA
Histones are proteins that have a positive charge, enabling them to bind to the negatively charged DNA
The linker DNA connects adjacent nucleosomes
The 10nm chromatin fiber (beads-on-a-string) is a result of the nucleosomes and linker DNA
The 30nm chromatin fiber is formed by the folding of the 10nm fiber. Various model exist, with different dimension and packing densities
This further compaction results in a more condensed structure necessary for cell division
Euchromatin is loosely packed chromatin active in transcription
Heterochromatin is tightly packed chromatin, generally inactive in transcription. There are two types, constitutive and facultative

Histone Octamer

The histone octamer is composed of two copies each of four core histone proteins: H2A, H2B, H3, and H4.
The core histones associate to form a dimer of H2A-H2B and a tetramer of H3-H4
These components form a protein complex that is crucial to DNA packaging.

Histone Fold

Histones have conserved motifs known as the histone fold
The histone fold motif is a common structural motif in histones (across species)
The histone fold motif is crucial for the dimerization (joining) of histones during octamer formation
The motif contains a long α-helix connected to two short helices and strands (HSH) at opposite ends. This motif is important for histone-histone interactions

Euchromatin and Heterochromatin

Euchromatin is lightly packed chromatin, which is active in transcription and contains genes that are being expressed.
Heterochromatin is tightly packed chromatin, which is generally inactive in transcription and contains repetitive DNA sequences
There are two types of heterochromatin: facultative (can change) heterochromatin and constitutive (permanent) heterochromatin. Constitutive heterochromatin typically contains regions like telomeres and centromeres and is often repetitive sequence

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Description

Explore the complex structure of DNA packaging through chromatin architecture. This quiz covers key concepts such as nucleosomes, histone proteins, and the differences between euchromatin and heterochromatin. Understand how DNA's organization is critical for cell division and transcription.