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Ch. 12 - DNA Organization in Chromosomes
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 12, Problem 9

Describe the molecular composition and arrangement of the components in the nucleosome.

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Begin by identifying the core components of a nucleosome, which include DNA and histone proteins.
Explain that the nucleosome consists of approximately 147 base pairs of DNA wrapped around a histone octamer.
Describe the histone octamer as being composed of two copies each of four different histone proteins: H2A, H2B, H3, and H4.
Clarify that the DNA wraps around the histone octamer in about 1.65 left-handed superhelical turns, which helps compact the DNA.
Mention the role of the linker histone H1, which binds to the DNA between nucleosomes and helps stabilize the higher-order chromatin structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nucleosome Structure

A nucleosome is the fundamental unit of chromatin, consisting of DNA wrapped around a histone protein core. It compacts DNA and regulates its accessibility, playing a key role in gene expression and DNA packaging.
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Chromosome Structure

Histone Proteins

Histones are positively charged proteins (H2A, H2B, H3, and H4) that form an octamer core around which DNA wraps. Their interaction with DNA helps neutralize negative charges and facilitates tight DNA packaging.
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DNA-Histone Interaction

Approximately 147 base pairs of DNA wrap around the histone octamer in about 1.65 turns. This interaction is stabilized by electrostatic forces and hydrogen bonds, enabling efficient DNA compaction while allowing dynamic access for cellular processes.
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