Lecture 9 Flashcards
each lamp brush chromosome consists of two aligned sets of –
paired chromatids
arrested at the diplotene stage of meiosis
oocyte
genes present in the loops are being
actively expressed
the – method of determing the position of loops in interphase chromosomes
chromosome conformation capture (3C)
cells treated with formaldehyde –>
covalent DNA-protein and DNA-DNA cross links
DNA is then treated with a restriction nuclease that chops the DNA into many pieces, cutting at strictly defined nucleotide sequences and forming sets of –
identical “cohesive hends”
cohesive end are made to join through their
complementary base pairing
Prior to the ligation step, DNA is diluted so that the fragments that have been kept in – )through cross-linking) are the ones most likely to join
close proximity
Reverse cross links (by heat treatment and proteolysis) and the newly ligated fragments of DNA are – and – by PCR
identified and quantified
DNA product is only observed by 3C if proteins hold the two DNA sequences –
close together in the cell
chromosome is folded into a series of –
looped domains
each loop domain contains
50,000 -200,000 nucleotide pairs
DNA keep replicating but cell not dividing –>
synthesize large amount of certain proteins
about – of the polytene DNA is in 3700 bands
95%
about – of the polytene is in 3700 interbands
5%
– in polytene chromosome puffs
RNA synthesis
chromatin loops – when the genes within them are expressed
decondense
each of the 46 human chromosomes tend to occupy – within the nucleus
its own discrete territory
nucleolus =
assembly of ribosome subunit and rRNA synthesis
heterochromatic regions are often associated with the –
nuclear lamina
T/F: the gene-rich regions are largely absent in the DNA near the nuclear envelope
true
most regions of our chromosome are folded into a conformation called
fractal globule every 5 megabase
fractal globule is a knot-free conformation that permits dense packing yet
retains an ability to easily fold and unfold
chromatin can move to specific sites to
alter gene expression
T/F: the position of a gene changes when it becomes highly transcribed
true
large loop of chromatin – when a gene is on
expands
network of – form a set of distinct biochemical environments inside the nucleus
proteins and RNA
Each chromosome at metaphase contains
two sister chromatids
each chromatid contains – generated by DNA replication
one of two identical sister DNA molecules
short region of DNA double helix
2 nm
histone core
11 nm
zig zag model of chromatin fiber of packed nucleosomes during interphase
30 nm
each DNA molecule has been packaged into a mitotic chromosome that is – shorter than its fully extended length
10,000 fold
