Activation of a zymogen is by covalent modification. How might phosphorylation or dephosphorylation (also covalent modification) modify an enzyme to make it more active (or more inactive)?

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All right. Hello everyone. So this question is asking us, how does phosphorylation result in the modification of an enzyme to either increase or decrease its activity? So here we have four different answer choices labeled A through D. Now, before we talk about phosphorylation in greater detail, I want to quickly point out two enter choices that we can go ahead and eliminate because that it has to do with the definition of phosphorylation. Option. C says that phosphorylation cleaves specific peptide bonds in the enzyme. That's incorrect. Option D says that phosphorylation adds a hydroxyl group to the enzyme that is also incorrect because recall that a phosphorylation involves the addition of a phosphate group. So that's why both of those answer choices are correct or incorrect. I should say now between options A and B option A says that phosphorylation causes a confirmational change in the enzyme. Whereas option B says that phosphorylation blocks the active site of the enzyme. Now, a few more things about phosphorylation, phosphorylation falls under covalent modification, which is one of many ways that enzymatic activity can be controlled. Now, in this particular case, coal modification describes the process in which an enzyme is regulated by physically changing the structure of the enzyme. You're either adding or removing groups from the polypeptide chain. Now, the effect of this makes sense, right? Because the vast majority of enzymes are actually proteins. I just realized that I spelled modification wrong. But as I was saying before, right, the vast majority of enzymes are proteins and proteins are very sensitive to their structure. So changing the structure is going to affect the enzyme. So in the most general sense, we can conclude that phosphorylation with the addition of this phosphate group is going to cause changes in the structure of the enzyme itself. Now, depending on where this change takes place, the activity of the enzyme can either increase or decrease. So here, that's precisely why we can eliminate Option B because option B says that phosphate groups always block the active site of the enzyme, therefore, decreasing its activity. That's not necessarily true because phosphorylation can happen either near the active site or even far away from the active site itself. Regardless the addition of that polar phosphate group is going to have some kind of change on the enzyme itself. Now, this enzyme can either increase or decrease its activity. But in this case, option A is going to be our best answer. So option A says that phosphorylation adds a phosphate group to the enzyme causing a confirmational change that increases its activity. Notice how option A doesn't specify where the phosphate group is added because that can vary. So that's why that's our best answer. And so with that being said, thank you so very much for watching. And I hope you found this helpful.

Activation of a zymogen is by covalent modification. How might phosphorylation or dephosphorylation (also covalent modification) modify an enzyme to make it more active (or more inactive)?

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Key Concepts

Zymogen Activation

Phosphorylation and Dephosphorylation

Enzyme Regulation