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SUMMARY:Symmetry\, Periodicity\, and Reversibility: New DNA Puzzles for Th
 e Passionate Scientists  - Kirti Prakash (University of Cambridge)
DTSTART:20190613T120000Z
DTEND:20190613T130000Z
UID:TALK126040@talks.cam.ac.uk
CONTACT:Anne Herrmann
DESCRIPTION:DNA is a long polymer with a double-helix geometry. A helix is
  probably the most refined structure by which two polymers may couple and 
 provide a pairing mechanism for maximally effective replication. The helix
  then wraps around octamers of histone proteins to form nucleosomes in a f
 ascinating beads-on-a-string structure. At the final order of compaction\,
  DNA organises itself into globules called chromosome territories. \n\nSom
 e outstanding questions in the chromosome biology are: how do 10-nm "bead-
 on-a-strings" nucleosomes fold into 1000-nm size chromosome territories? A
 re there intermediary chromatin domains? If so\, of what size and shape? A
 nd how do they regulate chromatin folding? Does 30-nm chromatin fibre exis
 t? Are chromosomes territories coacervates? \n\nWe have developed a new me
 thod to image DNA in high-resolution and found at least three distinct ord
 ers of chromatin states: 30-60 nm (active phase)\, 120-150 nm (repressed p
 hase) and 250-500 nm (inactive phase). These domains are organised in peri
 odic and symmetric compartments\, indicating the spatial organisation of a
 ctive and inactive regions of the genome. Moreover\, we found that\, under
  stress\, chromatin dynamically remodels and adapts to hollow\, condensed 
 ring and rod-like configurations\, which reverse back to the original stru
 cture when stress conditions cease. \n\nDNA\, nucleosomes\, nuclei\, cells
 \, tissues\, organs\, organisms\, and species are not random assignments o
 f evolution without design\, but factual realities arising from millions o
 f years of tinkering and optimization. Here\, I propose an alternative cla
 ssification of higher-order states of DNA based on domain sizes and topolo
 gical shapes. I also examine the biophysical aspects of DNA condensation a
 nd the role of sequence information (both nucleic and protein) in driving 
 the reversible folding of DNA.
LOCATION:MR11\, Centre for Mathematical Sciences\, Wilberforce Road\, Camb
 ridge
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