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Same Objective Lens:
Salivary gland- polytene chromosomes
Why are the
salivary gland
chromosomes
so much larger?
Alyssa and Tyler
Brain-diploid metaphase chromosomes
MPF (Cdk/Cyclin Protein Complexes)
Regulate Progression through Cell Cycle
SKIPPED in Polytene Tissues
(Salivary Gland)
MPF=
Cdk
_________ (Cyclindependent Kinase)
- regulates proteins by
phosphorylation
Cyclin
__________
- cell cycle phasespecific kinase
regulators
How might cell cycle regulation differ ?
Fig. 14.8
7x compaction
Chromatin Packaging
in Salivary
Gland Squash
throughout cell cycle
Chromatin: DNA Complexed
with Protein
40x compaction
Chromatin Packaging
in Metaphase
Chromosomes
10,000x10,000x
compaction
compactionFig. 12.12
M phase only
7x compaction
non-heat shocked
40x compaction
heat shocked
Compaction Level
Dark Bands?
30 nm fiber and higher
Light Interbands?
Lower than 30 nm fiber
10,000x10,000x
compaction
compactionFig. 12.12
Which proteins would you expect to co-localize with HP1 here?
HP1
HP1 in transcriptionally silenced
centromeric heterochromatin
HP1 binding to
Me-K9 histone H3
to silence
Transposable
Elements in
centromeric
heterochromatin
Fig. 12.17
Nucleosome
- ~200 bp DNA wrapped
around histone core
octamer containing
2 each of 2 different
heterodimers: histones
H2A/H2B and H3/H4
-ionic bonds between
(-) chgd. DNA backbone
and (+) chgd. histones
(20-30% Lys/Arg)
- highly conserved amino
acid sequence
- packing ratio 7:1
-N terminal tails-sites of
covalent modifications
Fig. 12.9
N-terminal Covalent
Modifications Give a
“Histone Code”
Acetylation: Active Chromatin
Deacetylation: Inactive Chromatin
Methylation ( K9H3, K27H3 , K20H4):
Heterochromatin
Fig. 12.14
7x compaction
non-heat shocked
40x compaction
heat shocked
Bands or Interbands?
Acetylated Histones?
De-acetylated Histones?
Interbands
Bands
10,000x10,000x
compaction
compactionFig. 12.12