10.11-10.20 Flashcards
where is the lampbrush chromosome found
amphibians
how are lampbrush chromosomes formed
extended meiosis over long period of time
where do lateral loops extrude from in lamp brush chromosomes
chromomere
what do the loops in lamp brush chromosomes contain
nascent RNA chains
an increase in RNP length (RNA chains) of lamp brush chromosomes indicates what?
transcription unit
where are polytene chromosomes found?
dipteran insect larvae, in interphase nuclei of salivary glands and imaginal discs
how are polytene chromosomes formed
multiple rounds of replication without mitosis (endomitosis, endoreplication)
what does polytene chromosome consist of
4 synapsed diploid pairs held together are chromocenter (where centromeres aggregate)
in situ hybridization
uses labeled probes for specific genes to illustrate position on cytological map
where are chromosome puffs found
polytene chromosomes
chromosome puff
transcriptionally active region in which chromosome fibers unwind from usual state of packaging
Balbiani ring
large puff (more than one gene tcr)
pattern of puffs is related to what?
gene expression
when does puffing pattern change
during larval development
composition of nucleosome
8 histone proteins (H2A, H2B, H3, H4) plus 2 wraps of DNA
what happens when you treat chromatin with micrococcal nuclease
releases individual nucleosomes and destroys linker DNA between them
true or false: m. nuclease is an endonuclease that is sequence blind
true
what does micrococcal nuclease digestion generate
a ladder of DNA fragments with about 200 bp increments
each step on ladder represents what?
DNA derived from discrete number of nucleosomes
how much of DNA is not packaged in nucleosomes?
very little
as time increases with micrococcal digestion, what happens to the number of long pieces of DNA
decreases
nucleosome core particle length of DNA
146 bp
mononucleosome
after initial m nuclease cut, about 200 bp of DNA
trimmed nucleosome
if m nuclease continues digesting, about 165 bp of DNA
final protected DNA length
146 bp of DNA
where is histone H1 located
in region of linker DNA immediately adjacent to core DNA
DNase I
seq blind, ss nicks in DNA
DNase II
seq blind, ds nicks in DNA
what do H3 and H4 form
tetramer
what does H3/H4 tetramer bind to
2 H2A/B dimers
where does binding of DNA to histone proteins occur
sugar-phosphate backbone
- sequence-independent
what part of the histone protein extends away from the nucleosome core
N-terminal tails - where modification occurs
does 10nm fiber of chromatin structure requires histone H1 for structure?
no
does 30nm fiber/solenoid of chromatin structure requires histone H1 for structure?
yes
how many levels of packaging needed for replication
at least 3
how many levels of packaging need for transcription
no more than 3
true or false: constitutive heterochromatin is transcribed
false, but it is replicated
CAF-1
protein at replication fork that binds to H3/4, helps them form tetramer, then helps add H2A/B dimers
how do nucleosomes change with replication
Meselson-Stahl - mixture of old/new histone proteins - semi-conservative closest model
