A solution of a globular protein is heated slowly at constant pressure. Differential scanning calorimetry shows an endothermic unfolding transition. Based on thermodynamic reasoning for phase/structural transitions, which conclusion can be drawn about the enthalpy change for unfolding at the transition?
- Unfolding has at the transition, consistent with heat absorption to disrupt stabilizing interactions. (correct answer)
- Unfolding has because endothermic peaks indicate heat release by the sample.
- Unfolding must have because only entropy changes during conformational changes.
- The sign of cannot be inferred from calorimetry because it measures only temperature, not heat.
Explanation: This question tests thermodynamic interpretation of calorimetry data for protein unfolding. An endothermic peak in DSC indicates heat absorption (ΔH >0) during unfolding, as energy is required to break stabilizing interactions. Thus, choice A is consistent with the transition. Choice B is incorrect because endothermic means heat absorption, not release. For similar problems, relate peak direction to process enthalpy. Verify baseline subtraction and scan rate effects on peak shape.