Enzyme Classification: Study with Video Lessons, Practice Problems & Examples

Enzymes are categorized into six main classes based on their catalytic functions: oxidoreductases (redox reactions), transferases (transfer of functional groups), hydrolases (break bonds using water), isomerases (rearrangement of functional groups), lyases (addition/removal of groups without hydrolysis), and ligases (covalent bonding using ATP). Each class has specific subclasses, enhancing the understanding of enzyme specificity and function. Recognizing these classifications aids in grasping metabolic pathways and enzyme kinetics, essential for studying biochemical processes.

Common Naming Concept 1

Now when it comes to the common naming of enzymes, we're going to say that unlike other compounds, enzymes are named based on their function rather than their structure. And we're going to say that we modify the ending of the substrate name by adding "ase" to the end. Our naming convention will be the substrate, and then the modifier is us just changing the ending to "ase." So, just remember, enzymes are a bit unique; we're looking at how they function rather than their structure in terms of giving their common name.

Common Naming Example 1

In this example question, it states, "If chitin, a polysaccharide, represents the substrate in a catalyzed reaction, using a common rule, determine the name of its enzyme." Alright. So, chitin here represents our substrate structure, and now we're going to talk about the enzyme. Remember, when it comes to naming the enzyme, all we do is modify the end by adding "ase." So here we have chitin, and then we would add "ase" to the end. So, the name of its enzyme would be chitinase. If we look at our options, this would be option b. So here, the enzyme for chitin, a polysaccharide, would be chitinase.

Systematic Naming Concept 2

Now when it comes to the systematic naming of enzymes, we're going to say in this case, for enzymes, the substrate attached and the type of catalyzed reaction can also determine the name. Under this system of naming, we're going to use a naming convention of substrate followed by the enzyme class. Later on, we'll learn about the different classes of enzymes and catalyzed reactions, and how those give us the overall systematic name for any given enzyme. Alright. So just keep this in mind as we investigate how to name enzymes under this type of rule.

Systematic Naming Example 2

So in this example question, it says, hydrotase is a class of enzyme that catalyzes the addition of water to a molecule. What will be the name of the enzyme used in the following reaction? So if we take a look at this reaction, we have Nyl CoA, which is this structure here. We're utilizing an enzyme. And if we look, we had initially this double bond here between the two carbons. Remember, carbon wants to make 4 bonds, so there's a hydrogen here and a hydrogen here that's invisible. If we look over here, these two carbons still have their hydrogens, but they have gained a water. This carbon has gained an OH, and this carbon here has gained an H. That's the addition of water. The addition of water has also removed the pi bond, the double bond that we had initially in our reactant. So remember, we're talking about systematic naming of an enzyme. And the naming convention is the substrate name, our substrate is our reactant, so this would be in the name. So B and D are out, and then we would add the class of enzyme that's being used. In this case, it's a hydrotase. So the name would be Nyl CoA hydrotase. This would be the enzyme that has allowed us to add water to our substrate reactant. So here, our answer would be option C. A doesn't work because we didn't talk about dehydratase here, and D usually means that we're doing the opposite where we're having the removal of water, which is not what's going on here. Our reactant is gaining water, not removing water. So again, our answer would be option C.

Six Main Classifications Concept 3

In this section, we'll talk about the 6 main classifications of our enzyme classes. Now, enzymes can be divided into 6 main classes based on the type of reaction catalyzed. And we're going to say here that classes are further divided into subclasses based on the type of substrate. So here we have a majority of the name for the 6 classes of enzymes. We're just missing the first letter. So how do we remember what those first letters are? Well, here we're going to say, what do enzymes do? Well, enzymes help speed up the rate of the reaction by lowering the energy of activation. They help reactions get over the hill. The hill representing that energy of activation, that hill that we have to traverse or get over to become products. So over the hill, o. So this is oxidoreductases, v, transferases, and then hill, these are hydrolases, isomerases, lyases, and ligases. So these are your different types of enzymes, the 6 classes of enzymes that we'll investigate. Remember, some of them can be further broken down into subclasses based on the substrate that's involved. Alright. So keep this in mind when we're talking about the different classes of enzymes that exist.

Oxidoreductases Concept 4

Now the first class of enzymes we'll talk about are our oxidoreductases. Here, they catalyze oxidation-reduction or redox reactions by transferring electrons between molecules. We've talked about redox reactions before. So remember, in this case, oxidation means the loss of hydrogen or the gaining of oxygen. And reduction, we're going to say is the opposite. It's the gaining of hydrogen, and you could lose more than one hydrogen, gain more than one oxygen. For reduction, you could gain more than one hydrogen and lose more than one oxygen. We have subclasses to this particular class of enzymes. The subclasses are oxidases and reductases. Oxidases, from the name, they oxidize a substance. Reductases, they reduce a substance.

If we take a look here at this reaction, we have a glucose molecule, and we are using the enzyme, glucose oxidase. This is written in the systematic name where we have the substrate name, which is glucose, followed by the class or subclass of enzyme. Here, the term 'oxidase' means that we're going to oxidize the glucose. What happens here is we have an alcohol, and remember, when we oxidize an alcohol, we're trying to make a carbonyl group. So, this carbon now is double-bonded to the oxygen. It's an oxidation because carbon has lost its hydrogen, and oxygen has formed a double bond with carbon. This indicates oxidation is occurring. We've gone from glucose, our starting material, used our enzyme to oxidize it, and created glucono delta-lactone. As a byproduct, we've made hydrogen peroxide. The key takeaway here is knowing that glucose is our substrate, and that glucose oxidase is the systematic name for our enzyme being used to oxidize the glucose. This is what we take away. And we have to remember that this represents an oxidoreductase type of reaction. So, keep that in mind when investigating this first class of enzymes.

Oxidoreductases Example 3

Here it says, which of the following is an indicator that a reaction is catalyzed by an oxidoreductase? So remember, this is the class of enzymes dealing with redox reactions. So we have reduction, which could represent the gaining of hydrogen or the loss of oxygens, or we can have oxidation where it's the gaining of oxygens or the loss of hydrogens. So here, let's look. Loss of a function group. Nope. That's not involved in redox. Loss of water. Still not involved in redox. Loss of hydrogen or loss of a substance. Substance is too vague, loss of what kind of substance? C is the right answer, loss of a hydrogen. Remember loss of a hydrogen in this case would be an example of oxidation. And in subclasses that is oxidases that help us. Alright. So here we'd say the answer would be option C.

Transferases Concept 5

In this video, we'll take a look at the 2nd class of enzymes. Here we have our transferases. Now, they catalyze the transfer of functional groups between molecules, and this one has subclasses. We have transaminases and kinases. Transaminase involves the transfer of an amino group, a nitrogen-containing group. Kinases deal with the transfer of a phosphate group. If we take a look here at our reaction, we have a glucose molecule as our substrate, and here we have ATP, remember that's just energy. Here we're going to have our Hexokinase involved. Since "Kinase" ends the name, it's going to deal with the transferring of a phosphate group. Now, what happens here is that ATP has some phosphate groups. This enzyme is going to help us take one of them away and it's going to get transferred. So the hydrogen here is going to be removed, so that one of the phosphate groups from ATP can attach to this structure here. So when we look over to the product side, we no longer have glucose, we have glucose 6-phosphate. Here, the hydrogen has been replaced with this phosphate group. ATP is no longer ATP because it's lost one of its phosphate, so now it's ADP, and the hydrogen that was replaced is just hanging around here as an H+. So the key takeaway from this is being able to recognize what has been transferred. We have a glucose molecule, the hydrogen from glucose has been transferred out for a phosphate. That is a key giveaway that we're dealing with a subclass of enzymes called kinases. Remember, transferase is just an enzyme that helps us to transfer functional groups between molecules, and kinases help us to transfer phosphate groups.

Transferases Example 4

Here it says, identify the type of enzyme subclass from the following reaction. If we take a look here, we have our beginning reactants, and we have an unknown enzyme, which is a question mark, and we're making these products. If we look, this chain here is similar to this chain here. And this chain here, which is larger in appearance, is this chain here. But what's the difference? Well, here, we didn't have a carbonyl group here, but now we do. And we're going to say that we didn't have an NH₃ group here. We had a carbonyl group there instead. So what happens is that this amino group got transferred over, and this carbonyl got transferred over. They kind of swapped places. We have the transferring of an amino group between molecules. And what subclass of enzymes are going to help us do that? We're going to say that it is a transaminase. So let's say our transaminase is a subclass of enzymes that was used to transfer our amino group from one molecule to another molecule.

Hydrolases Concept 6

In this video, we're going to talk about the third class of enzymes, and that is hydrolases. Now, in these types of enzymes, we catalyze hydrolysis reactions. Basically, it breaks bonds by adding water. With this type of class of enzymes, we have subclasses. One important thing to take away from this is that although these are hydrolases, none of them have "hydro" within their name. Okay, so that makes it a little bit more tricky in terms of remembering. But all of them will utilize water to break bonds.

For the first one, we have lipases; we're going to say they hydrolyze ester bonds in lipids. Next, we have proteases; they hydrolyze proteins into peptides and amino acids. So they're breaking down proteins into their less complex structures. Next, we have nucleases; they hydrolyze DNA and RNA into nucleic acids. And then finally, we have phosphatases; they hydrolyze phosphate ester bonds.

So here, if we take a look, we have this polypeptide, and we're going to utilize this protease. Remember, that helps to hydrolyze proteins into peptides and amino acids. It's going to break this polypeptide into smaller chunks. And we're going to be using the enzyme to help us cut or cleave this bond here. If we come over here, what has occurred? Well, we can see that we have severed this bond here and this carbon here is from the previous bond, and it's gained an O-. And then this nitrogen here is the same nitrogen here; it has gained two hydrogens. So what have we gained? We've gained two hydrogens plus one oxygen. So, we've added water to our polypeptide. Okay, so we use water to cut the bond and split it into two pieces. Right? So here, this is a great example of one of our subclasses of hydrolases. Remember, there's a lot of subclasses within this class of enzymes, but none of them have "hydro" within their name.

Hydrolases Example 5

Here in this example question, it says, which subclass of hydrolysis is responsible for the breakdown of triglycerides and other lipids into free fatty acids and glycerol. Alright. So, we're seeing a lot of terms here. What's the keyword? Lipids. And we know when it comes to lipids, the subclass of hydrolases that we would utilize are our lipases. Right? Lipase, lipid, lip, and lip. That's a key giveaway of what's going on here. Remember, we're changing the end of the substrate name to ace. Right? So lipid, we change the ending to ace, which is how we came up with lipase. Right? So just keep that in mind when taking a look at this particular example question. We do use lipases or lipase in order to cut these lipids into smaller fragments or smaller molecules.

Isomerases Concept 7

In this video, we're going to take a look at our 4th class of enzymes, our isomerases. So here we're going to say we have to catalyze the creation of an isomer by shifting functional groups to a different location within the same molecule. So in this reaction, we have dihydroxyacetone phosphate, and we're using an isomerase to help us to create Glyceraldehyde 3-phosphate. What has happened here? Well, we have this hydroxyl group which is at the end, and it got shifted over to our next carbon next door or adjacent carbon. And at the same time we had this carbonyl here, and it's now at the end. So they have shifted positions. This is an example of an isomerase. Also, notice that when it comes to this class of enzymes, we don't have subclasses. Alright. So we're just going to have an isomerase. It helps to create different isomers by moving functional groups to different locations within the same molecule.

Isomerases Example 6

Which of the following represents a reaction of an isomerase? Alright. So if we take a look at the first one, what's occurring here is that we have this hydrogen getting replaced by this phosphate group. So we're removing a phosphate group from ATP in order to do this. We're transferring a phosphate group. So this is a kinase. Kinase doesn't belong to the class called isomerases, so this would not work.

For the next one, it may look like we've done something to our starting material to create this other one, but we really haven't. If we were to number this in order to name it, we'd start off from this end: 1, 2, 3, 4, 5. Here, this would be 2-pentanone. And again, we've discussed naming ketones in earlier chapters. So it's going to be important that you are able to identify that these are the same molecule. Here would be 1, 2, 3, 4, 5. This is also 2-pentanone. Nothing has been done to this molecule; it's just been flipped and turned around to make it look like something has occurred. So this would be nothing.

For the next one, we have lost hydrogens here in order to make a pi bond here. We can say that this is a form of oxidation, we've lost hydrogen so we could say maybe an oxidase got involved here, something that helped us to lose hydrogen. And we know that that is not an isomerase. We didn't make an isomer by moving things around. So this would not work.

Now, by process of elimination, d is the answer. But why? Remember, an isomerase is making an isomer. An isomer has the same formula but different connections. And if we were to look at these 2 and add up all the carbons, all the hydrogens, all the oxygens, they both would have the same exact formula, but they look different. That's because they're isomers of each other. So this one was a bit tricky, but these are our answer. K? It may have been hard to see, but again, isomers, same molecular formula, different connections in this case. And because of that, because we have isomers, that means an isomerase had to have been used. Alright. So again, our answer would be d.

Lyases Concept 8

In this video, we'll take a look at the 5th class of enzymes, our lyases. Now here they catalyze the addition or removal of functional groups without hydrolysis or redox reactions. Here, the addition and removal of groups help to break and create double bonds respectively. With this type of enzyme class, we have subclasses. Our subclasses include dehydrogenases, which help to remove water; hydrotases help to add water. We have deaminases, which help to remove amino groups, so NH3. And then decarboxylases, this isn't as easy to see, but decarboxylation deals with the removal of CO2. If we take a look at our two reactions, we start out with fumarate here, and we're going to use fumerase or hydrotase, which means we're going to add water. We're adding water to this pi bond. So here, in order to add to those 2 carbons, we have to destroy the pi bond, remove it, and here's the water we added, in the form of OH and H.

Below that, we have Tyrosine. And with this Tyrosine, we're using Tyrosine decarboxylase. Remember, decarboxylation means a loss of CO2. The CO2 that we're going to lose is this one here. We lose that CO2. So now that carbon here has lost that CO2. It's gained a hydrogen to remake the loss because remember, carbon must make 4 bonds. And here goes the CO2 that was lost. So again, remember, here we're dealing with lyases and there are quite a few subclasses when it comes to this particular class of enzymes. So, keep that in mind to properly identify what exactly we are adding or removing to properly identify the subclass of enzyme.

Lyases Example 7

Here with this question, it says, which of the following subclasses of the enzyme is responsible for catalyzing reactions where a molecule undergoes non-hydrolytic cleavage forming multiple molecules without the addition or removal of water. Alright. So a bulk of this is describing our lyase as our subclass of an enzyme. Out of the options given, that means our answer is either option B or C. Here, phosphatases don't work, and transaminases don't work. They're not in this class of enzymes. But here's the key thing, they're saying without the addition or removal of water. Dehydratase, this deals with the removal of water, so it couldn't be option C. So, by process of elimination, it has to be option B. Deaminase has to do with the removal of an amino group \( \text{NH}_3 \). They never said anything about the removal of \( \text{NH}_3 \) here; they're talking about without the removal of water. That eliminates option C, but not option B. So again, option B will be our final answer.

Ligases Concept 9

In this video, we'll talk about the 6th class of enzymes, our ligases. Now here, they catalyze the covalent bonding of 2 molecules together with the use of ATP. So energy is required here. Now, we have 2 subclasses that belong to this class of enzymes. They are our synthetase and then our carboxylase. So, synthetases form a bond between 2 molecules. Carboxylases, they form a bond specifically between CO₂ and another molecule.

If we take a look here, we have pyruvate. And next to pyruvate, we have CO₂, the required ATP, and then our ligase in the form of pyruvate carboxylase. So, carboxylase means we want to add CO₂ to our pyruvate molecule. So, this CH₃ is going to have CO₂ added to it. To do this, we have to sacrifice one hydrogen from the carbon because carbon can only make up to 4 bonds. Doing this transforms pyruvate into oxaloacetate. And we're going to say here we also create what, ADP as a byproduct because we have to use a phosphate from ATP. And then we also have our acid here that's formed +H⁺. So again, this represents a carboxylase because we had the joining of a carbon dioxide molecule with pyruvate, another molecule.

Alright. So keep this in mind when looking into the 6th class of enzymes and the 2 subclasses that belong to it.

Ligases Example 8

So in this example question it says, during protein synthesis, blank enzyme catalyzes the attachment of an amino acid to a corresponding transfer RNA molecule through an ester bond. Alright. So here, we're joining two molecules to each other. So we know we're dealing with the ligase. And we're going to say that it could either be a synthetase or a carboxylase. It can't be a carboxylase because they never talked about joining carbon dioxide to either one of these molecules. So it has to be synthetase. So we're going to say here our synthetase enzyme is what's catalyzing the joining of these two molecules within this particular example question.

Summary of 6 Enzyme Classes Concept 10

So in this video, let's do a rundown of our 6 classes of enzymes. Alright. So here we have our enzyme classes, we have our reaction that's catalyzed, and then we have the description involved. So let's go down this list. For the first one, O, oxidoreductases. Here we have molecule A and molecule B. If we look on the other side, we can see that there are changes that have occurred. We can see that A has lost its 2 electrons and handed them over here to BH₃. So we have the transferring of electrons from A to B. A has lost its electrons, so here we'd say that A is being oxidized, B has gained those electrons, so we'd say that it is being reduced. So we're looking at a redox reaction here. Here we're gonna say the description is, redox reaction via transfer of electrons.

Next, we have T, transferases. Molecule A has this group here that's extending from it. And then if we look, that group has transferred from A to B. Now on the product side, B has that extending group. So here, this deals with the transfer of functional groups.

Next, we're gonna have H, hydrolases or hydrolase. Here we have A + B being connected together by this bond and we have water. Water is gonna be used to cut or cleave that bond. In the process, A got hydrogen and B got OH. Water has been added to break that bond. So here, the description is we break bonds by adding water.

Next, we have I, isomerases. A here, on that molecule, OH is on the right side of it. And then what's happened, it has been shifted over to the other side. Now, we just have to assume that A is not a symmetrical molecule, and there are differences from the right side and the left side, so that when OH transfers to the other side, it creates a brand-new structure. So here we're gonna have the rearrangement of atoms within a molecule to create isomers. Remember, isomers have the same formula, but here they're gonna have different connections.

Next, we have Lyases or lyases. So we have A and B connected. Here, that is severed and now we have A and B separate. Here we're gonna say the description is it breaks or forms bonds without redox reactions or water.

And then finally, we have Ligase or ligases, A + B require ATP in order to form a bond with each other on the product side. So here we use energy to covalently join molecules together. Alright. So this gives us a good rundown or summary of our 6 classes of enzymes.

Which of the following could be the possible name of enzyme that involves the transference of a phosphate group between substrates?

• A. Tyrosine Kinase 
• B. Cysteine Isomerase 
• C. Cellulase
• D. Glutamate deaminase

Which of the following enzyme name and function is incorrectly matched?

• A. Glucose Oxidase – Catalyzes the oxidation of the glucose molecule.
• B. Sucrase – Catalyzes the hydrolysis of sucrose. 
• C. Deaminase – Catalyzes the addition of NH₃ to a substrate. 
• D. Pepsin – Catalyzes the digestion of proteins from food that is consumed.

Which of the following statements is true of ethanal reductase?

• A. It represents a hydrolase that acts upon the ethanol substrate to oxidize it. 
• B. It represents an oxidoreductase that acts upon the ethanal substrate to oxidize it.
• C. It represents a lyase that acts upon the ethanal enzyme to reduce it. 
• D. It represents an oxidoreductase that acts upon the ethanal substrate to reduce it. 

Identify the class and subclass of an enzyme that catalyzes the following reaction.

• A. Lyase, Hydratase
• B. Hydrolase, Protease
• C. Lyase, Dehydratase
• D. Hydrolase, Nuclease

Which of the following catalyzes the given reaction involving a triglyceride?

• A. reductase
• B. lipase
• C. kinase
• D. decarboxylase

Here’s what students ask on this topic:

What are the six main classes of enzymes and their functions?

Enzymes are categorized into six main classes based on their catalytic functions:

• Oxidoreductases: Catalyze redox reactions by transferring electrons between molecules.
• Transferases: Transfer functional groups from one molecule to another.
• Hydrolases: Break bonds using water, facilitating hydrolysis reactions.
• Isomerases: Rearrange functional groups within a molecule to form isomers.
• Lyases: Add or remove groups to form double bonds without hydrolysis or redox reactions.
• Ligases: Catalyze the covalent bonding of two molecules using ATP.

Understanding these classes helps in studying metabolic pathways and enzyme kinetics.

How are enzymes systematically named?

Systematic naming of enzymes involves the substrate and the type of catalyzed reaction. The naming convention is typically the substrate name followed by the enzyme class. For example, in the enzyme glucose oxidase, 'glucose' is the substrate, and 'oxidase' indicates that it belongs to the oxidoreductase class, which catalyzes oxidation reactions. This systematic approach helps in identifying the specific function and reaction type of the enzyme.

What is the function of oxidoreductases?

Oxidoreductases catalyze oxidation-reduction (redox) reactions by transferring electrons between molecules. In these reactions, oxidation involves the loss of hydrogen or the gain of oxygen, while reduction involves the gain of hydrogen or the loss of oxygen. Subclasses include oxidases, which oxidize substances, and reductases, which reduce substances. An example is glucose oxidase, which oxidizes glucose to form gluconolactone and hydrogen peroxide.

What are the subclasses of transferases and their functions?

Transferases catalyze the transfer of functional groups between molecules. The main subclasses are:

• Transaminases: Transfer amino groups (NH₂) between molecules.
• Kinases: Transfer phosphate groups (PO₄^3-) from ATP to other molecules.

For example, hexokinase transfers a phosphate group from ATP to glucose, forming glucose-6-phosphate.

How do hydrolases function and what are their subclasses?

Hydrolases catalyze hydrolysis reactions, breaking bonds by adding water. Subclasses include:

• Lipases: Hydrolyze ester bonds in lipids.
• Proteases: Hydrolyze proteins into peptides and amino acids.
• Nucleases: Hydrolyze DNA and RNA into nucleotides.
• Phosphatases: Hydrolyze phosphate ester bonds.

For example, proteases break down proteins into smaller peptides and amino acids by adding water to peptide bonds.