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Qian, H.

Publications and source records attributed to Qian, H..

2 recordsLinked to original sources

Structure for Energy Cycle: A unique status of Second Law of Thermodynamics for living systems

Distinguishing things from beings, or matters from lives, is a fundamental question. Extending E. Schrodingers neg-entropy and I. Prigogines dissipative structure, we propose a chemical kinetic view that the earliest \"live\" process is essentially a special interaction between a pair of specific components under a corresponding, particular environmental conditions. The interaction exists as an inter-molecular-force-bond complex (IMFBC) that couples two separate chemical processes: One is the spontaneous formation of an IMFBC driven by the decrease of Gibbs free energy as a dissipative process; while the other is the disassembly of the IMFBC driven thermodynamically by free energy input from the environment. The two processes that are coupled by the IMFBC were originated independently and considered non-living on Earth, but the IMFBC coupling of the two can be considered as the earliest form of metabolism: This forms the first landmark on the path from things to a being. The dynamic formation and dissemblance of the IMFBCs, as composite individuals, follows a principle designated as \"... structure for energy for structure for energy...\", the cycle continues, shortly \"structure for energy cycle\". With additional features derived from an IMFBC, such as multiple intermediates, autocatalytic ability of one individual upon the formation of another, aqueous medium, and mutual beneficial relationship between formation of polypeptides and nucleic acids, etc., the IMFBC-centered \"live\" process spontaneously evolved into more complex living organisms with the characteristics one currently knows.

evolutionary biology

Phosphorylation energy and nonlinear kinetics as key determinants for G2/M transition in fission yeast cell cycle

The living cell is an open nonequilibrium biochemical system, where ATP hydrolysis serves as the energy source for a wide range of intracellular processes including the assurance for decision-making. In the fission yeast cell cycle, the transition from G2 phase to M phase is triggered by the activation of Cdc13/Cdc2 and Cdc25, and the deactivation of Wee1. Each of these three events involves a phosphorylation-dephosphorylation (PdP) cycle, and together they form a regulatory circuit with feedback loops. Almost all quantitative models for cellular networks in the past have invalid thermodynamics due to the assumption of irreversible enzyme kinetics. We constructed a thermodynamically realistic kinetic model of the G2/M circuit, and show that the phosphorylation energy ({Delta}G), which is determined by the cellular ATP/ADP ratio, critically controls the dynamics and the bistable nature of Cdc2 activation. Using fission yeast nucleoplasmic extract (YNPE), we are able to experimentally verify our model prediction that increased {Delta}G, being synergistic to the accumulation of Cdc13, drives the activation of Cdc2. Furthermore, Cdc2 activation exhibits bistability and hysteresis in response to changes in phosphorylation energy. These findings suggest that adequate maintenance of phosphorylation energy ensures the bistability and robustness of the activation of Cdc2 in the G2/M transition. Free energy might play a widespread role in biological decision-making processes, connecting thermodynamics with information processing in biology.

systems biology