Section 1: Chromatin and Nucleosome Fundamentals

What is the fundamental repeating unit of chromatin, often described as "beads on a string"?

The nucleosome.

What does a nucleosome core particle consist of?

An octamer of core histone proteins (two each of H2A, H2B, H3, and H4) around which approximately 147 base pairs of DNA are wrapped.

What is the role of the linker histone H1?

H1 binds to the DNA between nucleosomes, helping to compact chromatin into higher-order structures like the 30nm fiber.

Which parts of the core histones protrude from the nucleosome and are subject to post-translational modifications?

The N-terminal tails of H3, H4, and H2B, and both the N- and C-terminal tails of H2A.

Why are histone tails described as intrinsically disordered?

They are highly flexible and can move dynamically to perform different functions, such as interacting with other proteins and being modified.

Where is the DNA located in relation to the histone proteins within a nucleosome?

The DNA wraps around the outside of the histone octamer.

What was the significance of Roger Kornberg's 1974 nucleosome hypothesis?

He proposed that chromatin is based on a repeating unit of eight histone molecules and about 200 base pairs of DNA, which became the foundation for our understanding of nucleosome structure.

Why is the spatial positioning of nucleosomes along DNA critical for cellular processes?

It controls access to DNA for processes like gene expression, DNA replication, and repa