11.2: The Organization of Chromatin Flashcards
Individual chromosomes occupy () within the nucleus
distinct territories
chromosomes are organized in such a way that the transcriptional activity of a gene is related to its ()
position
() proposed that each chromosome occupies a distinct territory, with centromeres and telomeres attached to opposite sides of the nuclear envelope
Carl Rabl
Carl Rabl proposed that each chromosome occupies a distinct territory, with centromeres and telomeres attached to
opposite sides of the nuclear envelope
the 2 ways in which the organizations of chromosomes within the nucleus has been studied
- fluorescence in situ hybridization (FISH)
- chromosome conformation capture (3C)
this method uses probes that specifically detect repeated sequences on individual chromosomes, thus it has been used to visualize the location of chromosomes within a nucleus
fluorescence in situ hybridization (FISH)
this method identifies the sites of association between chromosomal regions, thus it has been used to analyze the interactions between different regions of chromosomes in living cells
chromosome conformation capture (3C)
how does 3C detect sites of association between chromosomal regions
sites of association are detected by cross-linking adjacent DNA sequences, which can then be amplified and identified by high-throughput sequencing
() divide each chromosome into distinct domains, so that the two arms of each chromosome don’t interact with one another
centromeres
highly condensed and transcriptionally inactive chromatin in interphase cells
heterochromatin
heterochromatin is usually associated with:
the nuclear envelop or the periphery of the nucleolus
decondensed and transcriptionally active chromatin in interphase cells
euchromatin
euchromatin is preferentially localized to
the interior of the nucleus or next to nuclear pore complexes
Chromatin within the nucleus is divided into (), restricting the interaction of chromosomal regions
looped domains
chromatin is organized in looped domains such that
regions within a domain interact frequently with one another, but only rarely interact with regions from other domains
the boundaries of these chromosomal domains contain binding sites for (1) and (2), the latter of which is thought to act as an architectural protein that regulates the organization of the genome
- cohesin
- CTCF
Heterochromatin is localized to the nuclear lamin by binding to
lamins and the lamin B receptor
chromatin domains associated with the nuclear lamina are called (); these cover about 40% of the human genome
lamina-associated domains or LADs
the binding of the lamin B receptor to () mediates the association of heterochromatin with the nuclear lamina
HP1
HP1 binds to methylated histone (), which are characteristic of transcriptionally inactive chromatin
H3 lysin 9 residues
chromatin domains associated with the nucleolus’ periphery are called
nucleolus-associated domains or NADs
genes found in LADs or NADs are generally
transcriptionally repressed
Chromosomes are divided into domains corresponding to (1) and (2)
- transcriptional units
- regions of chromatin modification
Replication and transcription take place within
clustered regions
DNA replication occurs within discrete regions called
replication factories
replication factories were initially defined by visualizing newly synthesized DNA by labeling cells with
bromodeoxyuridine
clustered sites of newly synthesized DNA also represent concentrated sites of the () involved in DNA replication
proteins
transcription also occurs at clustered sites called
transcription factories
transcription factories may also facilitate the () of related genes
coordinated regulation
