Final answer:
Enzymes involved in bread-making do not function at or above 45°C because high temperatures cause denaturation, which disrupts their essential three-dimensional structure and active site, leading to loss of function.
Step-by-step explanation:
The enzymes involved in bread-making will not function at or above 45°C because of a process known as denaturation, which disrupts the enzyme's three-dimensional structure. The enzyme's structure is crucial for its function, particularly at the active site where substrate binding occurs. At high temperatures, the weak bonds that maintain the enzyme's shape can break, leading to loss of function. Most enzymes have an optimum temperature range in which they function most efficiently, often close to the normal body temperature of the organism they are derived from, typically around 37°C. Exceeding this temperature, as in the case of the bread-making enzymes at 45°C or higher, results in the enzymes becoming less active or completely inactive due to denaturation.
Enzymatic activity varies with temperature; it typically increases as the temperature rises, up until a certain point, whereupon further increase in temperature causes a rapid decrease in activity. The critical temperature where enzymes begin to denature can vary, but for many proteins, it occurs between 45°C and 55°C. This is also the reason why food preservation techniques such as boiling and refrigeration affect the activity of enzymes, as they either denature enzymes through high heat or slow their activity through cooling.