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SUMMARY:What makes cellular decisions irreversible? - Prof. Béla Novák\,
  University of Oxford
DTSTART:20081022T130000Z
DTEND:20081022T140000Z
UID:TALK10655@talks.cam.ac.uk
CONTACT:Dr Fabien Petitcolas
DESCRIPTION:*Abstract*: Cells are making many decisions during their life\
 , when they select and find nutrients\, choose between alternative develop
 mental pathways etc. These decisions are triggered by molecular signals (s
 timulus) and they are concluded in a change of physiological state. If the
  decision is irreversible the cellular state reached after the transition 
 is stable even if the initial stimulus is inactivated. Classical examples 
 for irreversible transitions are provided by the eukaryotic cell cycle reg
 ulation. In an early stage of the cell cycle\, cells can choose between di
 fferent developmental scenarios: proliferation\, quiescence etc. However a
 fter passing through a point called ‘Start’ or ‘restriction point’
 \, cells become fully committed for cell division. It is common to explain
  these irreversible transitions by proteolytic degradation of certain regu
 latory proteins which is a thermodynamically irreversible process. However
  this simple and appealing view of irreversible cellular transitions is ba
 sed on ambiguous notion of ‘irreversibility’. I will argue that the ir
 reversible nature of cellular transitions is a systems-level property of t
 he underlying molecular control network. Therefore irreversibility transit
 ion of a molecular control system cannot be attributed to a single molecul
 e or reaction\, but derive rather from systems-level feedback signals. Thi
 s systems-level view of irreversibility is supported by theoretical consid
 erations and by many experimental observations.
LOCATION:Microsoft Research Ltd\, 7 J J Thomson Avenue (Off Madingley Road
 )\, Cambridge
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