chromatin structure and histone code Flashcards
1
Q
DNA packaging
A
Chromosomes + associated proteins = chromatin
Histones are proteins responsible for 1st level of packaging DNA + histones = nucleosomes Nucleosome structure increases DNA packaging 7-fold Nucleosomes pack themselves in fibers of 30nm constituting the 2nd level of packaging Increases packaging 6-fold 30nm fibers pack themselves into 80-100nm fibers constituting 3rd level of packaging Increases packaging 3-fold 4th level of packaging is represented by the mitotic chromosome Represents 10000-fold packaging
2
Q
Chromosomes consist predominantly of
A
DNA
Histone proteins Non-histone proteins Non-coding RNA
3
Q
Interphase chromosomes
A
Almost all DNA packaged at 1st level
Nucleosomes Much DNA is tightly packed in higher order structures
4
Q
Nucleosomes
A
Histones assemble to form an octamer core
2 molecules of histones H2A, H2B, H3 and H4 N-terminal tails outside the octamer core
5
Q
Higher order structure involves
A
Linker histones (e.g. H1)
Interaction of histone tails with adjacent nucleosomes Binding of packaging proteins to histone tails
6
Q
Chromatin
A
Structure is not static
During DNA transcription or DNA replication, nucleosomes must be removed form the front of the polymerase and replaced behind the polymerase Histone remodeling factors are enzymes that remove and replace nucleosomes
7
Q
Facultative heterochromatin
A
Contains genes not expressed in that cell type
DNA tightly packaged as heterochromatin But may be packaged as euchromatin in other cell types
8
Q
What determines whether nucleosomes are packed as euchromatin or heterochromatin?
A
Modification of lysine residues in histone tails by acetylation and methylation
