Enzyme Regulation: Covalent Modification - Video Tutorials & Practice Problems

Covalent Modification/Zymogens Concept 1

Now, remember, enzymes can be represented as protein molecules. And we're gonna say enzyme activity can be regulated by addition or removal of groups on the enzyme polypeptide chain. Now, here we have two types. We have what are called zymogen. Zymogen are what we call pro enzymes. And then we have what's called phosphorylation and dephosphorylation with Z zymogen. We're gonna say zymogen are enzymes produced in inactive forms with an extra polypeptide segment. Now they're activated by cleavage. Remember just cutting off of the extra polypeptide segment by hydrolysis. So if we take a look here in this first image, we have our enzyme and we can see that a vast majority of this enzyme is purple and we also have this grade portion here. This is the extra part of the polypeptide segment. And this would represent an inactive enzyme through hydrolysis. We're able to cut or cleave this great portion of my polypeptide chain. So now it's gone by removing it. We've just activated my enzyme. So this will represent my active enzyme, right? So just remember when we're talking about addition or removal. In this case, we're talking about removal of a portion of this polypeptide segment that transforms our inactive enzyme into now a active enzyme.

Zymogens Example 1

Here, it says which of the following statements is not relevant to zymogen. Remember, zymogen represent inactive enzymes that have an extra polypeptide segment that needs to be cut or cleaved off in order to activate the enzyme. So, zymogen are inactive because the excess polypeptide chain alters its overall structure. This is true. This is definitely relevant to a zymogen enzyme activity by loss of some part of the peptide chain is a type of covalent modification that is true and this also directly relates to zymogen. They exist in an inactive form because of that they have that extra segment to their polypeptide sequence or or chain cutting it off helps to make them active. All of this is a type of covalent modification. Now, trypsinogen is converted into active trypsin by hydrolysis of a hexapeptide segment from its backbone. Now, here this is showing us an example of a zymogen going from its inactive form to its active form. Here, Trypsinogen is the inactive form of my enzyme. It's the zymogen through hydrolysis, we're able to cut off a portion of its polypeptide chain and give us the active enzyme in the form of trypsin. So this is give us, giving us an exact example of a zymogen citric can attach to a non active site of the phospho fructose enzyme and decrease its activity. Remember when we're talking about zymogen, we're talking about cleaving or cutting off a portion of the polypeptide chain in order to go from an inactive form to an active form. This isn't even talking about cutting off. It's talking about attaching. This is not what we're talking about when referring to zymogen. So here, this is not related to zymogen. So here our final answer would be. Option D, we can see that A through C are talking about what we expect from a zymogen in an active form. Having a portion of it cleaved or cut off, changes it from an inactive form to an active form. D doesn't do that. So D would be the one that's not related to zymogen.

Phosphorylation/Dephosphorylation Concept 2

In this video, we'll take a look at phosphorylation versus dephosphorylation. Now, phosphorylation and dephosphorylation deals with the addition or removal of phosphate groups to the enzyme polypeptide chain and that alters the enzymes activity. So if we take a look here at phosphorylation, that means that we're adding a phosphate group. Here we have the inactive form of our enzyme. We'd use a kinase as the enzyme to do this, the kinase would help to attach a phosphate group to my enzyme. Here we show the phosphate group being represented by the letter P. By attaching that phosphate group to this enzyme, we are activating it. So in this case, we do phosphorylation in order to go from an inactive enzyme to an active enzyme. The opposite of phosphorylation is dephosphorylation. Here we have an inactive enzyme. In this case, in this case, it's inactive because it has a phosphate group attached. Some enzymes work when a phosphate group is attached, others only work once a phosphate group is removed. In order to remove this phosphate group through de phosphorylation, we use what's called a phosphatase. So phosphatase is the enzyme of choice to remove a phosphate group. So using it on this inactive enzyme, removes the phosphate group entirely and we go from an inactive enzyme to an active enzyme. So just remember, adding a phosphate group can help to activate an enzyme. Other cases, other enzymes work once we removed their phosphate groups. Kinas are the enzyme of choice for adding a phosphate group. Phosphatase is the enzyme to help us remove phosphate groups. Right. So this is what de um phosphorylation and dephosphorylation is in essence.

Phosphorylation/Dephosphorylation Example 2

In this example question, it says which of the following is true about covalent modification. All right. So here we're going to say a zymogen loses its activity when a peptide segment is removed from its primary structure. Remember, zymogen activation happens when we do remove a segment from the polypeptide chain. This is saying the exact opposite. It doesn't lose it, it gains next, additional removal of a phosphate group has no effect on enzyme activity. This is not true. Some enzymes are activated when we add a phosphate group, other enzymes are activated once we remove a phosphate group. So they do have an effect on the enzymes overall activity. A zymogen is activated by removal of hydroxyl groups from its polypeptide backbone. So we say that a segment of our polypeptide chain has to be removed. So we're talking about the amino acids. OK. That's what has to be removed. In order to facilitate zymogen activation, it's not just the hydroxyl groups that are removed. So this would not be true. So that leaves the last one phosphatase removes a phosphate group. Yes, that's true from an enzyme by breaking a covalent bond. In this case. Yes. The phosphate group that is at, that gets attached usually to the use of a kinase. In order to remove it, we use a phosphatase enzyme. This does result in the cleaving of the connection between the enzyme and phosphate group and that involves breaking a cove a bond. So here, this would be true about this particular covalent modification which has to deal with the removal of a phosphate group from an enzyme in order to activate it.