How would the lock-and-key model explain that sucrase hydrolyzes sucrose, but not lactose?

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All right. Hi everyone. So this question is asking to explain using the lock and key model why Pepsin can hydrolyze peptide bonds in proteins but not the glyco cytic bonds in starch. So to understand a question like this one, right, it's important to start by understanding what the lock and key model actually refers to the lock and key model if you recall is relevant for enzymes. And in this analogy in this model, right, the lock represents the enzyme itself and the key in this case represents the substrate of that particular enzyme just so we're clear the substrate is the starting material that the enzyme is acting on or the reaction to take place. Now, the reason why this analogy is important for this question and in general is because it explains why enzyme specificity is a product or excuse me, a property to take note of right, enzymes are very, very specific, not only to their substrate but also to the reaction that they catalyze. So here enzymes, the vast majority of enzymes I should say are proteins. And one thing to note about proteins is that their structure is very heavily coordinate with their function. The structure of a protein is best suited for its specific function. And so whatever reaction that an enzyme is responsible for catalyzing is going to do so at the active site, the active site is where the reaction is catalyzed. So if proteins or specifically enzymes which are proteins are very specific for their substrate, then their active site should also be very specific for the substrate and therefore for the reaction. And so if the job of Pepsin is to hydrolyze peptide bonds and peptide bonds alone, the active site is going to reflect that the shape of the active site should only facilitate the addition of a peptide bond and nothing else. So this brings us now to our question here, why peptide bonds and not the glyco cytic bonds in starch? Well, because a glyco cytic bond is going to have a different structure to a peptide bond, simply put it's not going to fit in the active site of Pepin because the active site of Pepsin was not designed to accommodate a glyco cytic bond. So here the key is the peptide bond and it's entering our lock, which is the active site of Pepsin. And so with that being said, we've arrived at our final answer which reads that Pepin's active site is specifically shaped to bind to peptide bonds in proteins and there you have it. So with that being said, thank you so very much for watching. And I hope you found this helpful.

How would the lock-and-key model explain that sucrase hydrolyzes sucrose, but not lactose?

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Key Concepts

Lock-and-Key Model

Enzyme Specificity

Substrate Structure