Blue Baroque

1
Blue Baroque
A performance-art piece by David Mason,
interpreted by G. Prody. Friday May 10, 8 pm,
Bellingham Unitarian Fellowship.
2
Each human cell has 2 meters of DNA. (E. coli
has 1.4 mm.)
The total length of DNA in an average person is
2 x 1010 km--
compare that to the earth's diameter of 4 x 104
km!!
A human liver cell nucleus has a diameter of µm
and must contain 46 chromosomes each ca. 4.3 cm
long. Since the largest human chromosome
contains 2.4 x 108 bp it would have a length of
8.2 cm if the DNA were stretched out in the B
conformation.
In fact, the length of this chromosome during
metaphase (when it is most condensed) is about
10 µm or about 1/8000 the length it could have
as B DNA!!!
3
?30 nm
MVA Fig. 28.12
4
VVP Fig. 27-31 Chromosome Puffs where
transcription is occurring.
5
How DNA looping, perhaps mediated by
nucleosomes, can bring enhancers into
contact with TAFs.
MVA Fig. 28.27
6
Chromatin structure and gene expression Region
of DNA containing an actively transcribed gene.
The region encompassing the transcribed gene
probably adopts the 10-nm configuration, whereas
sequences up- and downstream are organized into a
30-nm fibre. Transcription involves changes in
the chromatin structure that can be detected by
digestion with the endonuclease Dnase I.
Regions of general Dnase I sensitivity
correlate with acetylation of the histone tails,
defining a structural and functional 'domain' for
gene activity that is characteristic of 'open'
chromatin. This domain is embedded in regions
of higher chromatin compaction that are more
resistant to DNaseI digestion. This compacted
structure correlates with the presence of
deacetylated histones (blue wavy lines), and is
characteristic of 'closed' chromatin.
7
Demonstration that transcriptionally active genes
are more susceptible than inactive genes to DNase
I digestion. Chick embryo erythroblasts at 14
days actively synthesize globin, whereas cultured
undifferentiated MSB cells do not. Nuclei from
each type of cell were isolated and exposed to
increasing concentrations of DNase I. The
extracted nuclear DNA was treated BamHI, which
cleaves the DNA around the globin sequence and
normally releases a 4.6-kb globin fragment.
DNAs were subjected to Southern-blot analysis
with a probe of labeled cloned adult globin DNA,
which hybridizes to the 4.6-kb BamHI fragment.
DNA from the 14-day globin-synthesizing cells
was sensitive to DNase I digestion. Inactive DNA
from MSB cells was resistant to digestion. See
J. Stalder et al., 1980, Cell 19973.
8
(No Transcript)
9
MVA Fig. 28.28 Acetylation of histone cores on
lysines.
10
Experimental method for analyzing the
acetylation state of histones in chromatin
associated with a specific region of the genome.
Nucleosomes are lightly cross-linked to DNA in
vivo using a cell-permeable, reversible, chemical
cross-linking agent. Chromatin is then
isolated, sheared to an average length of three
nucleosomes, and subjected to immunoprecipitation
with an antibody specific for a particular
acetylated N-terminal histone sequence. The DNA
in the immunoprecipitated chromatin fragment is
released by reversing the cross-link and then is
quantitated using a sensitive PCR method. See S.
E. Rundlett et al., 1998, Nature 392831.


11
Transcriptional state of eukaryotic chromatin.
The ground state is generally restrictive, and
the enhancer (ENH) and promoter (TATA) elements
are covered by nucleosomes. Repressors (R) can
bind to the chromatin (either to the DNA or
nucleosome) and bind a set of proteins that
silence the DNA. Alternatively, the DNA can bind
activators (A) that bind to other chromatin
modifying proteins. These allow TFIID and RNA
polymerase II to replace nucleosomes and
initiate transcription.
12
(No Transcript)
13
Alberts Fig. 4-35
14
Histone modifications as chromatin codes.
Schematic representation of histone modifications
encountered on inactive and active gene loci. A.
Acetylation (Ac) of lysine (K) 12 on histone H4
and methylation (Me) of K9 on H3 are found at
inactive gene loci and are also enriched in
heterochromatin (orange circles and squares). B.
Acetylation on K9 and K14 of H3, methylation on
K4 of H3, acetylation on K5 of H4, and
methylation on arginine 3 of H4 are found at
gene loci that are either active or have the
potential to be (green circles and squares).
15
Alberts Fig. 4-35
16
Models for the generation and propagation of
histone codes. Recruitment of chromatin
modifiers including histone acetyl transferases
(HATs), histone deacetylases (HDACs) and histone
methyl transferases (HMTs) (coloured boxes)
through sequence-specific DNA-binding factors
(DBFs colored ovals) generate chromatin codes in
the vicinity of their cognate sites (similarly
colored rectangles on the DNA ribbon). Histone
modifiers that generate codes consistent with
gene inactivity are shown in orange, whereas
those that correlate with gene activity are shown
in green.
17
Immunology Antibodies
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
Ig Heavy MW Effector
functions class chain IgM
? 900,000 B-cell receptor Activates
complement IgG ? 150,000 Crosses
placenta Binds to Fc receptors of
phagocytes Activates complement IgA
? 150,000-600,000 Mucosal transport IgE
? 190,000 Induces mast cell degranulation IgD ?
150,000 B-cell receptor
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
Class switching
33
(No Transcript)