Final answer:
Allosteric enzymes can follow either the sequential or concerted model, with each detailing the changes in enzyme conformation upon substrate binding. The induced fit model is a more accurate representation than the lock-and-key model as it considers the dynamic nature of enzyme-substrate interactions where both enzyme and substrate undergo structural changes. Specifically, hexokinase changes its conformation in the presence of glucose according to the induced fit model.
Step-by-step explanation:
Sequential and Concerted Model of Allosteric Enzymes
The discussion revolves around two different models mentioned in the question: the sequential model and the concerted (or MWC) model of allosteric enzymes. These are two theories that describe how enzymes can change their shape and functionality in response to the binding of substrates or other effector molecules.
The sequential model suggests that enzymes have multiple binding sites, and the binding of a substrate to one site can induce a change in the shape of other sites, which can increase or decrease the enzyme's affinity for additional substrate molecules. On the other hand, the concerted model, proposed by Monod, Wyman, and Changeux (MWC), posits that all subunits of an enzyme switch between an active and an inactive form simultaneously and synergistically.
When it comes to allosteric enzymes, the more accurate model of enzyme-substrate interaction is the induced fit model rather than the lock-and-key model. The induced fit model accounts for the dynamic nature of enzyme conformational changes upon substrate binding, which does alter the shape of both the enzyme and substrate to facilitate the reaction. This concept is further supported by findings from X-ray crystallography studies.
In the specific case of hexokinase and glucose interaction mentioned, the correct answer is that hexokinase changes conformation in the presence of glucose. This highlights that enzymes are not rigid structures, but rather flexible molecules that undergo conformational changes upon substrate binding, a principle central to the induced fit model.
While some enzymes do have multiple allosteric sites that interact with each other, hexokinase operates under the induced fit model where the enzyme-substrate complex formation involves changes in both parties leading to the catalysis of the reaction.