By shifting the balance between conformational entropy and internal energy, polymers modifytheir shape under external stimuli, such as changes in temperature. Prominent among suchtransformations is the coil-globule transition, whereby a polymer can switch from an entropydominated coil conformation to a globular one, governed by energy. The nature of the coilglobule transition has remained elusive, with evidence for both continuous and discontinuoustransitions, with the two-state behaviour of proteins as an instance of the latter. Theoreticalmodels mostly predict second-order transitions. Here we introduce a model that takes intoconsideration hitherto neglected features common to any polymer. We show that a firstorder phase transition smoothly appears as a function of the model parameters. our resultscan relieve part of the conflicts between theory and experiments in the field of protein folding,in the wake of recent studies tracing back the remarkable properties of proteins to basicpolymer physics.
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