title: Information dynamics in living systems: prokaryotes, eukaryotes, and cancer.
abstract: BACKGROUND
  Living systems use information and energy to maintain stable entropy while far from thermodynamic equilibrium. The underlying first principles have not been established.
  
  
  RESULTS
  We propose that stable entropy in living systems, in the absence of thermodynamic equilibrium, requires an information extremum (maximum or minimum), which is invariant to first order perturbations. Proliferation and death represent key feedback mechanisms that promote stability even in a non-equilibrium state. A system moves to low or high information depending on its energy status, as the benefit of information in maintaining and increasing order is balanced against its energy cost. Prokaryotes, which lack specialized energy-producing organelles (mitochondria), are energy-limited and constrained to an information minimum. Acquisition of mitochondria is viewed as a critical evolutionary step that, by allowing eukaryotes to achieve a sufficiently high energy state, permitted a phase transition to an information maximum. This state, in contrast to the prokaryote minima, allowed evolution of complex, multicellular organisms. A special case is a malignant cell, which is modeled as a phase transition from a maximum to minimum information state. The minimum leads to a predicted power-law governing the in situ growth that is confirmed by studies measuring growth of small breast cancers.
  
  
  CONCLUSIONS
  We find living systems achieve a stable entropic state by maintaining an extreme level of information. The evolutionary divergence of prokaryotes and eukaryotes resulted from acquisition of specialized energy organelles that allowed transition from information minima to maxima, respectively. Carcinogenesis represents a reverse transition: of an information maximum to minimum. The progressive information loss is evident in accumulating mutations, disordered morphology, and functional decline characteristics of human cancers. The findings suggest energy restriction is a critical first step that triggers the genetic mutations that drive somatic evolution of the malignant phenotype.
authors.affiliation: College of Optical Science, University of Arizona, Tucson, Arizona, United States of America.
authors.forename: B Roy
authors.initials: BR
authors.lastname: Frieden
authors.forename: Robert A
authors.initials: RA
authors.lastname: Gatenby
mesh_terms: D049109:Cell Proliferation; D019277:Entropy; D005057:Eukaryotic Cells / Q000378:metabolism*; D006019:Glycolysis; D006801:Humans; D007257:Information Theory; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D011387:Prokaryotic Cells / Q000378:metabolism*