Lesson plan

Loop entropy

Loop entropy is the entropy lost upon bringing together two residues of a polymer within a prescribed distance. For a single loop, the entropy varies logarithmically with the number of residues N in the loop : \Delta S = \alpha k_{B} \ln N \, where k_{B} is the Boltzmann constant and \alpha is a coefficient that depends on the properties of the polymer. This entropy formula corresponds to a power-law distribution P \sim N^{-\alpha} for the probability of the residues contacting. The loop entropy may also vary with the position of the contacting residues. Residues near the ends of the polymer are more likely to contact (quantitatively, have a lower \alpha ) than those in the middle (i.e., far from the ends), primarily due to excluded volume effects.

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Article summary

Loop entropy is the entropy lost upon bringing together two residues of a polymer within a prescribed distance. For a single loop, the entropy varies logarithmically with the number of residues N in the loop : \Delta S = \alpha k_{B} \ln N \, where k_{B} is the Boltzmann constant and \alpha is a coefficient that depends on the properties of the polymer. This entropy formula corresponds to a power-law distribution P \sim N^{-\alpha} for the probability of the residues contacting. The loop entropy may also vary with the position of the contacting residues. Residues near the ends of the polymer are more likely to contact (quantitatively, have a lower \alpha ) than those in the middle (i.e., far from the ends), primarily due to excluded volume effects.

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