Chromatin & DNA Packaging

Chromatin

This is a complex of DNA & proteins found in Eukaryotic cells; the primary function is to package long DNA molecules into more compact, denser structures.

Euchromatin

This is lightly packed chromatin that is rich in gene concentration & is most often under active transcription.

Heterochromatin

This is tightly packed chromatin consisting mainly of genetically inactive sequences.

Constitutive Heterochromatin

This is very gene poor; centromeres and telomeres.

Facultative Heterochromatin

This can change heterochromatin to euchromatin and back; gene silencing.

Folded Fiber Model

This model found few or no free fiber ends & concluded each chromatid must consist of a single fiber.

Nucleosome Model

This is the most commonly accepted model for DNA packaging.

Nucleosome

This is the simplest packaging structure of all Eukaryotic chromatin; localized areas of transcription; better fit for protein biosynthesis.

Core Histones

These consist of appx. 120 amino acids each (H2A, H2B, H3, and H4).

Core Histones

These are highly conserved during evolution and in combination, form the core particle.

Linker Histone

This consists of appx. 200 amino acids (H1).

Linker Histone

This has tissue-specific expression & is not highly conserved. It is loosely associated with core particles.

10nm Fiber

This is responsible for the primary packaging of the chromatin.

30nm Fiber (Solenoid)

This is responsible for the helical coiling of 10nm fibers consisting of 6 nucleosomes.

Linker Histone (H1)

This histone is responsible for packaging (compaction of DNA around nucleosome).

Supercoiling

This reduces the length of DNA by ~7 times.

Histone H1

This histone binds 2 distinct regions of DNA: linker DNA and a portion of the 146 bp core.

metaphase

The final level of compaction is the ___________________ chromosome.

Nucleosomes, Solenoids, Chromatin Loops, Condensed Chromatin, & Chromatin folded around protein scaffold

Condensation occurs in stages: