Chapter 8: Chromatin

A set of flashcards covering key concepts related to chromatin, nucleosomes, and histones from Chapter 8 of LEWIN'S GENES XII.

What is a nucleosome?

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

What are histone tails?

Flexible amino- or carboxy-terminal regions of core histones that extend beyond the nucleosome's surface and are sites of extensive posttranslational modification.

What is the significance of the 10 nm fiber?

A linear array of nucleosomes generated by unfolding the natural condition of chromatin.

What is a linker histone?

A family of histones (such as histone H1) that bind nucleosomes and/or linker DNA, promoting the formation of the 30 nm fiber.

What is the 30 nm fiber?

A coil of nucleosomes and the basic level of organization of nucleosomes in chromatin.

What role does MNase play in studying nucleosomes?

MNase cleaves linker DNA and releases individual nucleosomes from chromatin, allowing for the study of their structure.

How long is the core DNA typically found in nucleosomes?

The core DNA is typically 145–147 bp in length.

What is the histone code hypothesis?

A proposal that specific combinations of histone modifications define the function of local regions of chromatin.

What modifications can histones undergo?

Histones can be modified by methylation, acetylation, phosphorylation, ubiquitylation, and sumoylation.

How does DNA wrap around histone octamers?

DNA is wrapped approximately 1.67 times around the histone octamer.

What are TADs?

Topologically associated domains that average about 1 megabase in size and allow for frequent interaction within but less frequent with adjacent domains.

What is the function of insulators in chromatin?

Insulators define transcriptionally independent domains and block passage of activating or inactivating effects from enhancers, silencers, and other control elements.

What occurs during nucleosome assembly in vivo?

H3-H4 tetramers bind DNA first, followed by the addition of two H2A-H2B dimers to form the complete nucleosome.

What happens to nucleosomes during transcription?

Nucleosomes are displaced by RNA polymerase during transcription, but reassociate with DNA after polymerase passes.

What is translational positioning?

The location of a histone octamer at successive turns of the double helix, determining which sequences are in linker regions.

What is rotational positioning?

The location of the histone octamer relative to the turns of the DNA double helix, determining the exposure of DNA on the nucleosome's surface.