Question

Describe the nucleosome/”beads on a string” level of chromatin. Be sure to include the roles of histones H2A, H2B, H3, H4.

Describe whether euchromatin or heterochromatin can result in increased gene expression and why.

True or False. If the statement is false, rewrite the sentence so that it is a true statement.

⦁   ATP-chromatin remodeling complexes condense chromatin, resulting is less gene expression.
⦁   In a dividing/mitotic cell, euchromatin is more abundant than heterochromatin

Answer 1

Chromatin is a complex and protein found in a eukaryotic cells. The primary protein components of chromatin are histones, and there are three levels of chromatin organization which includes DNA wraps around histone proteins , and forming nucleosomes and also called beads on a string structure.

Nucleosome interconnected by linker DNA and in addition to core histones, there is a H1 which contacts the exit or entry of the DNA strand on the nucleosome. So the nucleosome with core particle called H1 and with about 20 to 60 base pairs of linker DNA forms approximately , 10nm beads on a string fibre.

Role of H2A occurs in the cell nucleus by DNA modification, protein responsible for nuclear import of H2A protein are karyopherin and importin. Nucleosome assembly protein 1 is used to transport of H2A into the nucleus so it can wrap DNA. Each nucleosome composed of histone octamer which includes H2A, H2B, H3 and H4. Newly assembled H2A and H2B are released and are incorporated into new nucleosomes , they assembled into dimers which also assists nucleosome sliding. H3 and H4 randomly distributed on the newly synthesized DNA, they assembled by the RCAF that contains the subunit Asf1, so that they retain their chemical modification which contributes to the passing down of the epigenetic structure. And the newly synthesized H3 and H4 proteins in the new nucleosomes acetylated at different lysin residues as a part of the chromatin maturation process.

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