At what temperature do proteins start to denature?

Proteins begin to denature at temperatures around 60 degrees Celsius. This temperature typically represents a threshold for disrupting the weak interactions that maintain a protein's three-dimensional structure, such as hydrogen bonds and van der Waals forces. As the temperature rises, the kinetic energy of the molecules increases, leading to more frequent and vigorous molecular interactions that can ultimately unfold the protein structure.

Denaturation is a critical concept in biochemistry, as the active conformation of a protein is essential for its functionality. Different proteins have varying stability and denaturation temperatures, but 60 degrees Celsius is a commonly referenced point where many proteins start to lose their functional characteristics. This makes 60 degrees the most appropriate choice for the onset of protein denaturation among the given options.