Enzymes, which are proteins, play a crucial role in everyday life processes. Without enzymes, the digestion of food, such as carbohydrates, fats, and sugars, would take years to generate a usable amount of energy. Enzymes are best known as biological catalysts because they accelerate biochemical reactions. For example, pepsin, an enzyme, when released in the stomach helps in the digestion of proteins. An enzyme binds to a substrate (reactant) in a very specific manner, forming an enzyme-substrate complex. The enzyme-substrate complex then converts the substrate into the product. Once the reaction is complete, the product is released, and the enzyme is once again available to interact with new substrates. The enzyme is neither consumed nor changed after the reaction is complete. It is a catalyst that alters the reaction pathway and decreases the time required to form products. Enzymes are specific to one reaction or reaction type, and hence the mechanism by which enzymes work is known as the lock-and-key model of enzymes. According to this model, an enzyme has specific structural features that complement the reacting molecule or molecules. Which of the following statements are true with respect to enzyme activity?
a. Enzyme reactivity is not affected by change in pH and temperature.
b. Enzymes speed up the reaction rate.
c. The activation energy of a reaction increases when an enzyme is used to catalyze the reaction.
d. Enzymes affect the reaction pathway by forming an enzyme-substrate complex.
e. Enzymes are regenerated when the reaction is completed.