Final answer:
The true statement about A. enzymes is that after catalysis, enzymes can resume their original shape to interact with new substrate molecules. Enzymes are not used up in reactions, have specific active sites for their substrates, and generally function within a narrow pH range.
Step-by-step explanation:
Among the options given concerning the structure and function of enzymes, the correct statement is that after an enzyme has catalyzed a reaction, it resumes its original shape and can interact with a new substrate molecule. This is because enzymes are not consumed in the reactions they catalyze; rather, they facilitate the transformation of substrates into products and then become available to catalyze additional reactions. The statement about the apoenzyme and holoenzyme is not accurate as an apoenzyme becomes an active holoenzyme only upon binding to a cofactor or coenzyme.
Not all enzymes require cofactors for their function; some are active without these additional non-protein molecules. Competitive inhibition occurs when an inhibitor binds to the enzyme's active site, not an allosteric site. Finally, enzymes typically have an optimal pH range within which they function most efficiently, and can be very sensitive to changes in pH.
Enzymes serve as biological catalysts that accelerate chemical reactions without being consumed in the process. They possess unique active sites tailored to specific substrates, ensuring high selectivity for the reactions they catalyze. When an enzyme-substrate complex forms, the enzyme enables the conversion of the substrate to a product, and then releases the product and becomes ready to catalyze a new reaction.