8.592 - HST.452J (Spring 2022)
Statistical Physics in Biology
Lecture 29
(Please note that lecture is being recorded)
8.592 in 4-265 on 05/02/2022 at 2:30PM
Chromatin Organization
Determinants of nucleosome position
Sequence dependent positioning
AAATTT... repels nucleosomes, possibly due to rigidity
Nucleosome attracting sequences; typically composed of AA, TT, AT and more flexible(and possibly bent) in
one direction
Statistical positioning
Erlang distribution
for probability of k non-overlapping nucleosomes in an interval
Genome packing
Wrapping aroud nucleosomes of persistent DNA provides a compression factor of roughly 5
Chromatin fibre packed into nucleus (size 7-25\mu m)
Persistence length of the chromatin fibre should be of the order of 3-5 nuclesomes (each around 10nm in size) for 30-50nm
Treated as a random walk, a chromosome of 10^9 would occupy a size of around 30\mu m, possible in large oocytes
Expectations for the size of a polymer segment of size s in the random walk, and when confined to a size D
However, measurements of R(s)~s^{1/3} appear to indicate a different behavior for chromatin
Chromosome Conformation Capture
(Job Dekker) provides a measure of connectivity
Hi Glass
(viewer of Hi-C data)
The hard problem is to infer 3d structure from Hi-C data, can instead look at statistical properties
The fractal globule
model seems to fit some statistical aspects of the data
Lecture notes
8.592
lecture- last update 5/1/22 by M. Kardar