The enzyme sucrase catalyzes the hydrolysis of the disaccharide sucrose but not the disaccharide lactose. Does the induced-fit or lock-and-key model explain the action of sucrase better? Explain.

Question

Accepted Answer

Everybody. Our next question says, the enzyme hexose catalyzes the phosphorylation of glucose but not fructose. Which model better explains the action of hexose. A lock and key model. The enzymes active site has a specific rigid shape that perfectly matches the glucose molecule allowing it to catalyze the reaction efficiently. B induced fit model. The enzyme's active site undergoes a confirmational change upon binding glucose which allows it to effectively catalyze the phosphorylation of glucose. See lock and key model. The enzyme's active site is flexible and adapt significantly to the shape of the substrate. Explaining why it does not work with fructose or D induced Fit model. The enzyme's active site remains rigid and does not adjust to fit the glucose molecule. So first off, we can eliminate two of our answer choices as being incorrect definitions of our two models. So choice C has lock and key model is the name of the model and it says the enzymes active site is flexible and adapts significantly. But the lock and key model describes a situation where the enzymes active site is rigid and it does not change shape. So it fits the subs shape perfectly and does not change shape in the course of catalyzing the reaction. So the way a key fits into a lock all the time and just that specific key um is the notion of the lock and key model. And then choice d the induced fit model is described as the enzymes active site remaining rigid. But that's the lock and key model. The induced fit model says that the enzyme changes shape when the substrate binds And then that new shape is the one that is efficiently catalyzes the reaction. One thing to note is that in the induced fit model, the enzyme and substrate or the active site and the substrate already resemble each other closely. So they have a similar shape, just not that exact fit that you describe in the lock and key model. So that explains the specificity of the enzyme substrate interaction. So now we have our other two choices which correctly describe the two models, but which is the one we would use for our enzyme. Well, we might be tempted to say lock and key because this is talking about the fact that it catalyzes the phosphor relation of glucose but not fructose. So it's specific to glucose. But induced Fit model is just a better model in general is of most enzymes. And it does also show specificity because we know that the enzyme's active site resembles the shape of the substrate. So that explains its specificity and why fructose would not bind its shape is not similar enough to the active site. But then once that glucose comes into the active site and binds, you have your confirmational change that you then will catalyze the reaction. So as I say, the lock and key model doesn't really correctly describe the action of this enzyme where you have sort of a more open stage for the substrate to come in and then a closed stage for the reaction to be catalyzed. So again, our model that best describes the action of hexokinase and its specificity for glucose but not fructose is choice B. The induced fit model. See you in the next video.

The enzyme sucrase catalyzes the hydrolysis of the disaccharide sucrose but not the disaccharide lactose. Does the induced-fit or lock-and-key model explain the action of sucrase better? Explain.

Verified video answer for a similar problem:

Key Concepts

Induced-Fit Model

Lock-and-Key Model

Enzyme Specificity