Unit 5: Chromatin

Flashcards covering key concepts related to nucleosomes and chromatin organization.

Nucleosome

The basic structural subunit of chromatin, consisting of 200 bp of DNA and an octamer of histone proteins.

Histones

DNA binding proteins that are part of nucleosome structure, including flexible N- or C-terminal regions.

10 nm fiber

A fiber generated from the linear array of nucleosomes in chromatin.

30 nm fiber

A coil of nucleosomes that serves as a basic level of organization in chromatin.

Linker histones

Histones that are not components of the nucleosome core, binding nucleosomes and/or linker DNA.

Micrococcal nuclease

An enzyme that cleaves linker DNA and releases individual nucleosomes from chromatin.

Core DNA

147 bp in length, found on core particles produced by prolonged nucleosome digestion.

Histone tails

Flexible N-terminal and C-terminal regions of histones that extend beyond the nucleosome.

N-terminal tails

Histone tails that help lock DNA on the nucleosome, distributing evenly throughout its surface.

Histone modifications

Covalent modifications to histone proteins, including methylation, acetylation, and phosphorylation.

CenH3/CENP-A

A histone variant that replaces H3 in nucleosomes of DNA regions associated with the kinetochore.

H3.3

A histone variant expressed throughout the cell cycle, often available for assembly at regions of active transcription.

H2AX

A histone variant that is targeted by phosphorylation events associated with DNA damage and repair.

Acetylation

A histone modification that neutralizes the positive charge of lysine, increasing DNA accessibility for transcription.

Methylation

A modification of lysine or arginine residues in histones that can affect chromatin structure.

Nucleosome positioning

The arrangement of nucleosomes based on DNA sequences and the action of DNA-binding proteins.

Extrinsic positioning

Nucleosome assembly preferentially at a particular site due to adjacent proteins and exclusion of nucleosome binding.

Nucleosome remodeling

Active changes in nucleosome structure, including sliding, ejection, and histone exchange.

Insulators

Elements that separate gene domains from one another, preventing interaction between enhancers and promoters.

Chromatin spreading

The process by which heterochromatin spreads across a gene, influencing its expression.