Nucleosome

Definition

A nucleosome is the fundamental unit of chromatin, consisting of a segment of DNA wound around a core of eight histone proteins. It helps in packaging DNA into a more compact structure within the nucleus.

5 Must Know Facts For Your Next Test

1. Each nucleosome consists of approximately 147 base pairs of DNA wrapped around an octamer of histone proteins.
2. The histone octamer is composed of two copies each of histones H2A, H2B, H3, and H4.
3. Nucleosomes are connected by linker DNA and associated with the histone H1 protein to form a structure known as the chromatosome.
4. They play a critical role in regulating gene expression by controlling access to DNA sequences for transcription machinery.
5. During cell division, nucleosomes help ensure that DNA is accurately replicated and distributed to daughter cells.

Review Questions

• What components make up the core structure of a nucleosome?
• How many base pairs of DNA typically wrap around a single nucleosome?
• Why are nucleosomes important for gene regulation?

Related terms

Chromatin: Chromatin is a complex of DNA and protein found in eukaryotic cells that packages long DNA molecules into more compact structures.

Histones: Histones are basic proteins that help organize and package DNA into structural units called nucleosomes.

Chromatosome: A chromatosome consists of a nucleosome plus one molecule of histone H1 which helps further compact the chromatin fiber.