We introduce the first comprehensive molecular model of spider dragline elasticity which clearly integrates most of the information known to date about the structure of the fiber. In accordance with X-ray evidence, the dragline is represented by a large number of small crystallites separated by amorphous regions made of rubber-like chains. Our model results clearly indicate the important role of the crystallites which act as multifunctional cross-links and create inside the amorphous regions a thin layer with modulus higher than in the bulk. The role of the crystallites in spider silk is found to be amazingly similar to that speculated for carbon black in synthesized elastomers.

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A stochastic Monte Carlo approach, based on the kinetic theory of fracture, has been used to study the axial maximum tensile strength of polymer fibers. The approach is entirely microscopic and the inhomogeneous distribution of the external stress among atomic bonds near the chain ends is explicitly taken into account. Both primary and secondary bonds are assumed to break during fracture of the polymer fiber. The approach has been applied to perfectly oriented and ordered polyethylene fibers, for which approximate values of the model's parameters were obtained from experiment. Stress-strain curves have been calculated for several fibers of various (monodisperse) molecular weights and predictions for the tensile strength have been compared to experimental values.

We present an analysis of glycolysis based on experimental findings and an interpretation based on concepts of efficiency, resonance response, and control features available in highly nonlinear reaction kinetics. We begin with a model for the glycolytic mechanism that is comprehensive, includes a large number of known activations and inhibitions of enzymes by metabolites, and couples the phosphofructokinase (PFKase) and the pyruvate kinase (PKase) reactions. Fru-1,6-P2, PEP, P-e-Prv; PK, PKase; PYR, Prv; AK, AKase.the ATP/ADP ratio and the free energy dissipation in an extended range of the kinetic parameters as a function of the driving force for the glycolytic pathway, a measure of which is the total adenine nucleotide concentration [A(MDT)P]. We find substantial agreement of the calculated results with experimental findings, except for the insufficiently represented (GAPDHase/PGKase) reactions. Our model shows that the average ATP/ADP ratio is increased and the average free-energy dissipation is decreased in an oscillatory compared with a steady-state mode of operation. Furthermore, the average values of the ATP/ADP ratio and of the free-energy dissipation change abruptly past the onset of sustained oscillations. MODEL Description. Fig. 1

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