The induced fit model of enzyme action fine tunes the original concept of the lock and key model and modifies it. this induced fit model changes the original explanation by hypothesizing that a) enzymes' active sites are modified to fit substrates and initiate a chemical reaction. b) enzymes catalyze reactions between products to make substrates, while they remain unchanged themselves. c) enzymes catalyze reactions between products to make substrates. they are consumed in these sets of reactions. d) enzymes catalyze reactions that change substrates to make products. they are consumed in these sets of reactions.