阿財&小球

According to the text book "THE CELL"(5th edition), the Chapter 4, Page 211

1) Nucleosomes are a basic unit of eukaryotic chromosome structure.

2) The nucleosome, a protein-DNA complex discovered in 1974.

3) The complex of both classes of protein(Histone & Nonhistone chromosomal proteins) with the nuclear DNA of eukaruotic cells is known as chromatin.

4) Each individual nucleosome core partical consists of a complex of 8 histone proteins - two molecules each of histones H2A, H2B, H3, & H4 - and double-stranded DNA that is 147 nucleotide pairs long.  

The Chapter 4, Page 220

5) Two types of chromatin in the interphase nuclei of many higher eukaryotic cells: a highly condensed form, called Heterochromatin(silenced gene), and all the rest, which is less condensed, called euchromatin(expressed gene).

The Chapter 4, Page 222 & 223

6) The amino acid side chains of the 4histones in the nucleosome core are subject to a remarkable variety of covalent modifications, including the acetylation of lysines, the mono-, di-, tri-methylation of lysines, and the phosphorylation of serines, which occur on the 8 relatively unstructured N-terminal "histone tails" that protrude from the nucleosime. (All the covalent modification of histones are reversible.)

7) The specific enzymes are reponsible for creating or remving the Ac/Me/P group from each side chains, including HATs/KATs(Histone Acetyl Transferases), HDACs(Histone Deacetylase complexes), Histone Methyl Transferase, Histone Demethylation Compiexes, atc.

8) The Ac of lysines on the terminal tails tends to loosen chromatin structure, in part because adding an acetyl group to lysine removes its positive charge, thereby reducing the affinity of the tails for adjacent nucleisomes. (Ac -> remove [+] of lysine -> reduced the affinity of the tail -> lossen the chromatin)