Problems 10.94 and 10.95 both mention enzymes that hydrolyze peptide bonds. How do you account for the fact that pepsin has a high catalytic activity at pH 1.5 but chymotrypsin has very little activity at pH 1.5?

Question

Accepted Answer

All right. Hello everyone. So this question says that enzymes have specific PH ranges in which they are most active and this range can differ significantly between enzymes. Why does lysozyme exhibit high catalytic activity at ph six where the optimal PH is around 5 to 6? While Pepsin optimal Ph at two shows minimal activity at the same. Ph. So here we have four different answer choices labeled A through D which we'll discuss individually later on in this video for now, it's important to just recognize that in general enzymes have what are called optimal conditions and these optimal conditions are going to depend on the function of the enzyme and also where they perform that function, what environment they perform their function in. And so the optimal conditions describe, for example, the appropriate temperature and ph at which the enzyme is most effective. And this is because enzymes, most of which are proteins are very, very sensitive to their environment. This is because the structure of a protein is going to heavily dictate its function. And so if the interactions between amino acid side chains are disrupted because of things like changing the temperature or Ph the enzyme is at risk of unfolding, which means that it would not be effective any longer. So, going back now to the statement given and also specifically what enzymes we're comparing here, we have lysozyme operating optimally at a PH of around six versus Pepin which operates at around ph two. Now, this is because pepsin is found in your stomach and your stomach being highly acidic is going to require enzymes that can function in that acidic environment. And so if we also compare the information, given, we can see that lysozyme has a range of around five and six or between P five and six. Whereas Pepin is described to operate within a narrower ph range here, the question says PH two. So from here, let's go ahead and analyze our answer choices. A says that lysine requires highly acidic conditions to function optimally, which is why it extends high activity at ph six. While Pepsin is not affected by Ph changes. This statement is not accurate, right? Because as mentioned in the text of the question, Pepsin is minimally active at this Ph. This is because it is Pepsin that is suited for highly acidic conditions and not lysozyme. Lysozyme functions at a near neutral PH but slightly acidic, nowhere near as acidic as Pepsin. Though option B on the other hand says that lysozyme is less sensitive to PH changes and can operate across a broader Ph range. While Pepsin has a narrow Ph range for activity and becomes inactive at ph six. This is true, right? Because of the range for lysozyme is broader than the range for Pepsin and the PH of the solution, which is six is closer to the optimal ph of lysine compared to Pepsin. So B is correct. C on the other hand says that lysozyme is inactivated by acidic conditions, which is why it performed better at PH six. While Pepsin is optimized for neutral conditions, this is incorrect, right? Because Lysine, excuse me, Pepsin is the one that's optimized for acidic conditions. And if we're taking what the question says at face value, if lysozyme is inactivated by acidic conditions, it would not perform better at PH six. If the enzyme is inactivated, it would perform worse at a given ph. So this brings us now to option D which says that Pepsin is adapted to function effectively at a near neutral ph. Whereas Lysine requires a highly acidic environment to maintain its catalytic activity. Now, this question or excuse me, this statement is not correct and it's actually the other way around, it's Pepsin that's requiring a highly acidic environment whereas lysozyme operates at a near neutral Ph. So there you have it after all is said and done, our correct answer is going to be option B in the multiple choice. And so with that being said, thank you so very much for watching. And I hope you found this helpful

Problems 10.94 and 10.95 both mention enzymes that hydrolyze peptide bonds. How do you account for the fact that pepsin has a high catalytic activity at pH 1.5 but chymotrypsin has very little activity at pH 1.5?

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Key Concepts

Enzyme Catalysis

pH and Enzyme Activity

Specificity of Enzymes