---
title: "Chromatin: Nucleosomes and Higher-Order Packing"
description: "Two metres of DNA fit in a nucleus by wrapping around histone cores and coiling those into thicker fibres. The packing is not just storage: how tightly a region is packed decides whether it can be rea"
canonical: https://lightmysky.com/learn/science/chromatin-nucleosomes-and-higher-order-packing-mt_5q3Hsdqm9x
source: https://lightmysky.com/learn/science/chromatin-nucleosomes-and-higher-order-packing-mt_5q3Hsdqm9x.md
retrieved: 2026-09-12
---

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# Chromatin: Nucleosomes and Higher-Order Packing

Two metres of DNA fit in a nucleus by wrapping around histone cores and coiling those into thicker fibres. The packing is not just storage: how tightly a region is packed decides whether it can be read.

Subject: Science · Area: Genetics & Evolution · Ages 18 to 20
Page: https://lightmysky.com/learn/science/chromatin-nucleosomes-and-higher-order-packing-mt_5q3Hsdqm9x

## Ready when they can

- Describes the levels of packing from bare DNA to a condensed chromosome with rough scale at each level.
- Explains why histones bind DNA regardless of sequence, using the charge on each.
- Links a tightly packed region to low transcription without claiming the genes are absent.

## Lesson: Packing two metres of DNA into a nucleus

Your cells pack about two metres of DNA into a nucleus you cannot see. The bare helix is only two nanometres wide. It wraps about twice around beads called nucleosomes, each eleven nanometres wide, and those coils stack into a thirty nanometre fibre that loops into a chromosome a few micrometres long.

Each bead holds eight histone proteins. DNA grips them whatever the letters say, because the grip is electric. The DNA backbone carries a negative charge and histones carry a positive one, so they cling by charge, not by sequence.

**Example.** Picture two copies of one gene. One sits in loose beads where the reading machinery can land, so it gets read. The other sits in tight coils where the machinery cannot land, so it stays quiet, though the gene is still there.

**Tip.** Tight packing means silent, not missing. When a test asks, link low reading to closed packing, and never claim the genes are gone.

**Recap.** Charge wraps DNA onto beads, coils hide it, and tight regions stay present but unread.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Transcription and RNA Splicing in Eukaryotes](https://lightmysky.com/learn/science/transcription-and-rna-splicing-in-eukaryotes-mt_j2vc70vH5t)
- [DNA Structure and Base Pairing](https://lightmysky.com/learn/science/dna-structure-and-base-pairing-mt_PK4uNJeg_k)

## Opens up

- [Enhancers, Accessibility and Combinatorial Control](https://lightmysky.com/learn/science/enhancers-accessibility-and-combinatorial-control-mt_BTMCj6V6jD)
- [Replication Machinery: Origins, Forks and Telomeres](https://lightmysky.com/learn/science/replication-machinery-origins-forks-and-telomeres-mt_v95MJWeV_B)
- [Mapping Regulatory Elements: Accessibility, Occupancy and Contact](https://lightmysky.com/learn/science/mapping-regulatory-elements-accessibility-occupancy-and-contact-mt_W2YKGBADJ-)