Types of Enzymes: Videos & Practice Problems

Enzymes are categorized into six major classes: oxidoreductases, transferases, hydrolyases, isomerases, lyases, and ligases. Oxidoreductases facilitate oxidation-reduction reactions by transferring electrons, while transferases catalyze the transfer of functional groups. Hydrolyases break bonds using water, and isomerases rearrange atoms to form isomers. Lyases create or break bonds without redox reactions or water, and ligases join molecules using energy, often from ATP. Understanding these classes is crucial for grasping metabolic pathways and enzyme functions in biological systems.

Types of Enzymes

Enzymes are crucial biological catalysts that facilitate chemical reactions in living organisms. They are categorized into six major classes, each defined by the type of reaction they catalyze. These classes are:

• Oxidoreductases: Enzymes that catalyze oxidation-reduction reactions, where the transfer of electrons occurs.
• Transferases: Enzymes that transfer functional groups from one molecule to another.
• Hydrolases: Enzymes that catalyze the hydrolysis of various bonds, breaking down molecules by adding water.
• Isomerases: Enzymes that catalyze the rearrangement of atoms within a molecule, converting it into its isomer.
• Lyases: Enzymes that catalyze the addition or removal of groups to form double bonds or break them without hydrolysis or oxidation.
• Ligases: Enzymes that join two molecules together, often using energy derived from ATP.

To remember these classes, one effective mnemonic is the phrase "over the hill," where each letter corresponds to the first letter of each enzyme class. This visualization can help in understanding how enzymes lower the activation energy required for reactions, effectively helping them "get over the hill." Enzymes achieve this by stabilizing the transition state, which is a temporary state during the reaction process.

As you continue your studies, recognizing the specific reactions catalyzed by each enzyme class will be essential for mastering biochemistry concepts. The next focus will be on oxidoreductases, the first class of enzymes, which play a vital role in metabolic processes.

Types of Enzymes

Enzymes play a crucial role in biochemical reactions, and they can be categorized into six major classes. One of these classes is oxidoreductases, which are responsible for catalyzing oxidation-reduction (redox) reactions. These reactions involve the transfer of electrons between molecules, where substances that lose electrons are oxidized, and those that gain electrons are reduced. A helpful mnemonic to remember this concept is "LEO the lion goes GER," where "LEO" stands for "Lose Electrons is Oxidation" and "GER" stands for "Gain Electrons is Reduction." This phrase serves as a reminder of the fundamental principles of redox reactions.

In redox reactions, the transfer of hydrogen or oxygen atoms between molecules often indicates that an oxidation-reduction process is occurring. A classic example of an oxidoreductase is lactate dehydrogenase (LDH), which is vital for anaerobic respiration. The reaction catalyzed by LDH involves the conversion of L-lactate and NAD⁺ into pyruvate, NADH, and an acid. In this reaction, NAD⁺ is reduced to NADH, indicating that it has gained electrons, while L-lactate is oxidized, meaning it has lost electrons.

To analyze the reaction further, we observe that NAD⁺ gains a hydrogen atom, which is associated with electrons. This hydride shift signifies that NAD⁺ is not only gaining a hydrogen but also the electrons tied to it, confirming its reduction. Conversely, L-lactate loses electrons during this process, leading to its oxidation. Although the overall charge of pyruvate remains the same as L-lactate, the presence of the acid produced in the reaction accounts for the expected increase in positive charge due to the loss of electrons from L-lactate.

Additionally, the structural changes in the molecules provide insight into the oxidation process. Pyruvate has more bonds to oxygen than L-lactate, and an increase in oxygen bonds typically correlates with oxidation. Thus, understanding the roles of oxidoreductases and the principles of redox reactions is essential for grasping the biochemical processes that sustain life.

Which of the following is an indicator that a reaction is catalyzed by an oxidoreductase?

• A. Loss of a functional group.
• B. Loss of H₂O.
• C. Loss of a hydrogen.
• D. Loss of a substrate.

Answer: (C)

Types of Enzymes

In the study of enzymes, transferases represent a crucial class that facilitates the transfer of functional groups between molecules. These enzymes play a vital role in various biochemical processes, including metabolism. A prime example of a transferase is aminotransferase, which is responsible for transferring amino groups. One specific aminotransferase, alanine transaminase, is essential for the metabolism of the amino acid alanine.

Alanine transaminase catalyzes the conversion of L-alanine into pyruvate. During this reaction, it transfers the amino group from L-alanine to α-ketoglutarate, resulting in the formation of L-glutamate. The overall reaction can be summarized as follows:

\[\text{L-alanine} + \alpha\text{-ketoglutarate} \rightleftharpoons \text{pyruvate} + \text{L-glutamate}\]

This process highlights the dual role of alanine transaminase in both the deamination of L-alanine and the amination of α-ketoglutarate. Understanding the function of transferases is essential, as they are integral to numerous metabolic pathways. Recognizing that enzymes that catalyze the transfer of functional groups are classified as transferases will aid in identifying their roles in biochemical reactions.

Kinases add phosphate groups to molecules. Kinases are an example of which class of enzyme?

• A. Oxidoreductase.
• B. Phosphorylase.
• C. Hydrolyase.
• D. Transferase.

Answer: (D)

Types of Enzymes

In the study of enzymes, hydrolyases represent the third major class, following oxidoreductases and transferases. Hydrolyases are crucial enzymes that facilitate hydrolysis reactions, which involve the breaking of chemical bonds through the addition of water. The prefix "hydro" signifies water, highlighting the role of this molecule in the reaction process.

There are various types of hydrolyases, including peptidases, lipases, and nucleases, each responsible for hydrolyzing different biomolecules: peptidases break down proteins, lipases target lipids, and nucleases act on nucleic acids. A notable example of a peptidase is trypsin, which cleaves peptide bonds specifically after amino acids with lysine or arginine as their side chains. This specificity is illustrated in the hydrolysis of a polypeptide chain, where trypsin cleaves the peptide bond in the presence of water, resulting in the formation of polypeptide fragments.

During the hydrolysis process, water molecules contribute to the formation of the products. For instance, when a peptide bond is cleaved, water is incorporated into the resulting amino group and carboxylate group, effectively splitting the polypeptide into smaller fragments. Understanding the mechanisms and types of hydrolyases is essential as we progress in our exploration of enzymatic functions and their applications in biological systems.

Below is a reaction in the oxidative phase of the pentose phosphate pathway catalyzed by the enzyme gluconolactonase. This enzyme would be classified as what type?

• A. Transferase.
• B. Hydrolyase.
• C. Lyase.
• D. Isomerase.

Answer: (B)

Types of Enzymes

In the study of enzymes, isomerases represent the fourth major class, following oxidoreductases, transferases, and hydrolyases. Isomerases are specialized enzymes that facilitate the conversion of a molecule into its isomer by rearranging its functional groups without altering the overall chemical formula. This means that isomers share the same molecular composition but differ in the arrangement of their atoms.

A prime example of an isomerase is triosephosphate isomerase, which plays a crucial role in glycolysis. This enzyme catalyzes the transformation of dihydroxyacetone phosphate (DHAP) into glyceraldehyde 3-phosphate (G3P). Both DHAP and G3P have the same chemical formula, yet they are distinct isomers due to their different structural arrangements. Specifically, DHAP features a hydroxyl group at one end and a carbonyl group in the middle, while G3P has the carbonyl group positioned at one end and the hydroxyl group in the middle.

This rearrangement of functional groups exemplifies the function of isomerases, highlighting their importance in metabolic pathways such as glycolysis. Understanding the role of isomerases, like triosephosphate isomerase, is essential for grasping the complexities of biochemical reactions and the interconversion of metabolic intermediates.

What class of enzyme is required to convert a cis-fatty acid into a trans-fatty acid?

• A. Oxidoreductase.
• B. Isomerase.
• C. Hydrolyase.
• D. Lyase.

Answer: (B)

Types of Enzymes

In the study of enzymes, lyases represent a crucial class characterized by their ability to form or break chemical bonds without involving redox reactions or the addition of water. These enzymes typically engage in addition-elimination reactions, which are familiar concepts from organic chemistry. A key feature of lyases is their role in creating or removing double bonds or cyclic structures during these reactions.

A classic example of a lyase is pyruvate decarboxylase, which catalyzes the conversion of pyruvate into acetaldehyde and carbon dioxide. In this reaction, a bond is broken, resulting in the release of carbon dioxide. Notably, the reaction demonstrates a change in the number of double bonds: the reactants contain two double bonds, while the products contain three. This increase in double bonds serves as an indicator that the reaction is catalyzed by a lyase.

It is essential to recognize that the reaction is balanced, meaning the total number and types of atoms on both sides of the equation are equal. For instance, if we analyze the oxygen atoms, there are three on the left and three on the right, confirming that no water is added to facilitate bond breaking. Instead, a hydrogen atom is incorporated into the product, while carbon dioxide is released, further emphasizing that this process does not involve electron transfer, distinguishing it from oxidation-reduction reactions.

Understanding these characteristics of lyases, particularly through the example of pyruvate decarboxylase, lays a foundation for recognizing and applying these concepts in future biochemical contexts.

Which of the following best describes the function of a lyase enzyme?

• A. To facilitate a reaction where two substrates form one product without the use of water.
• B. To facilitate a reaction where one substrate forms two products with the use of water.
• C. To cleave bonds via the transfer of electrons between molecules.
• D. To tell fibs.

Answer: (A)

Types of Enzymes

Ligases represent the sixth and final major class of enzymes, playing a crucial role in biochemical processes. These enzymes utilize energy sources, such as ATP, to catalyze the ligation, or covalent joining, of two separate molecules into a single entity. A prime example of a ligase is DNA ligase, which is essential for DNA replication—a topic that will be explored in greater detail later in the course.

In the context of DNA, ligases facilitate the joining of distinct DNA strands by catalyzing reactions between specific functional groups. This process is vital for maintaining the integrity of the genetic material during replication. For instance, DNA ligase employs ATP to drive the reaction, ensuring that the separate DNA molecules are covalently bonded together.

Additionally, it is important to note that magnesium acts as a cofactor for DNA ligase, enhancing its enzymatic activity. This highlights the significance of cofactors in enzymatic reactions, which will be discussed in the upcoming lessons. Understanding the function of ligases and their cofactors is essential for grasping the complexities of molecular biology and the mechanisms underlying DNA replication.

Types of Enzymes

Enzymes are biological catalysts that facilitate chemical reactions by lowering the activation energy required for those reactions to occur. There are six major classes of enzymes, which can be remembered using the mnemonic "Just Over The Hill." Each letter corresponds to a specific class: O for oxidoreductases, T for transferases, H for hydrolyases, I for isomerases, L for lyases, and L for ligases.

Oxidoreductases are responsible for catalyzing oxidation-reduction (redox) reactions, which involve the transfer of electrons between molecules. A helpful mnemonic for remembering this process is "LEO the lion goes grrr," where LEO stands for "Lose Electrons Oxidation" and GER stands for "Gain Electrons Reduction." In this context, when a molecule loses electrons, it is oxidized, while the molecule gaining electrons is reduced.

Transferases, as the name suggests, transfer functional groups between molecules. This process is essential for various metabolic pathways, allowing for the modification of molecules through the addition of new functional groups.

Hydrolyases break chemical bonds by adding water, a process known as hydrolysis. This class of enzymes is crucial for the digestion of complex molecules, as they cleave bonds in substrates by incorporating water molecules.

Isomerases facilitate the rearrangement of atoms within a molecule, resulting in the formation of isomers. This class of enzymes plays a vital role in metabolic pathways by converting one isomer into another without altering the molecular formula.

Lyases are unique in that they can either break or form bonds without the involvement of redox reactions or water. They are characterized by changes in the number of double bonds or the formation/loss of rings in the substrate molecules.

Finally, ligases utilize energy, often from ATP, to covalently join two molecules together. This process is essential for synthesizing larger biomolecules and is a key step in various biosynthetic pathways.

Understanding these six classes of enzymes and the types of reactions they catalyze is fundamental for studying biochemistry and molecular biology, as they play critical roles in metabolic processes and cellular functions.

The presence of an electron acceptor such as NAD ⁺ indicates which class of enzyme?

• A. Oxidoreductase.
• B. Isomerase.
• C. Hydrolyase.
• D. Transferase.

Answer: (A)

Digestive enzymes are all examples of which class of enzyme?

• A. Ligase.
• B. Lyase.
• C. Hydrolyase.
• D. Transferase.

Answer: (C)

The reaction below is catalyzed by the enzyme arginase. What is the classification of this enzyme?

• A. Hydrolyase.
• B. Oxidoreductase.
• C. Lyase.
• D. Ligase.

Answer: (A)

Which class of enzyme catalyzes a reaction where the chemical formula does not change?

• A. Isomerase.
• B. Oxidoreductase.
• C. Transferase.
• D. Ligase.

Answer: (A)

What class of enzyme is required to combine two molecules using ATP?

• A. Lyase.
• B. Transferase.
• C. Oxidoreductase.
• D. Ligase.

Answer: (D)

Here’s what students ask on this topic:

What are the six major classes of enzymes?

The six major classes of enzymes are oxidoreductases, transferases, hydrolyases, isomerases, lyases, and ligases. Oxidoreductases facilitate oxidation-reduction reactions by transferring electrons. Transferases catalyze the transfer of functional groups between molecules. Hydrolyases break bonds using water, a process known as hydrolysis. Isomerases rearrange atoms within a molecule to form isomers. Lyases create or break bonds without the involvement of redox reactions or water, often forming or removing double bonds or rings. Ligases use energy, typically from ATP, to covalently join two molecules together. Understanding these classes is crucial for grasping metabolic pathways and enzyme functions in biological systems.

How do oxidoreductases function in biochemical reactions?

Oxidoreductases function by catalyzing oxidation-reduction (redox) reactions, which involve the transfer of electrons between molecules. In these reactions, one molecule loses electrons (is oxidized) while another gains electrons (is reduced). A common mnemonic to remember this is 'LEO the lion says GER,' where LEO stands for 'Lose Electrons Oxidation' and GER stands for 'Gain Electrons Reduction.' An example of an oxidoreductase is lactate dehydrogenase, which converts lactate and NAD⁺ into pyruvate, NADH, and H⁺. This enzyme is crucial for anaerobic respiration. Recognizing the role of oxidoreductases helps in understanding various metabolic pathways and energy production in cells.

What is the role of transferases in metabolic processes?

Transferases play a crucial role in metabolic processes by catalyzing the transfer of functional groups from one molecule to another. This transfer is essential for various biochemical pathways, including amino acid metabolism and nucleotide synthesis. For example, aminotransferases transfer amino groups between amino acids and keto acids, facilitating the synthesis and degradation of amino acids. A specific example is alanine transaminase, which converts L-alanine to pyruvate while transferring the amino group to α-ketoglutarate, forming L-glutamate. Understanding transferases is vital for comprehending how cells regulate and execute complex biochemical reactions.

How do hydrolyases catalyze reactions?

Hydrolyases catalyze reactions by breaking chemical bonds through the addition of water, a process known as hydrolysis. These enzymes are essential for the degradation of various biomolecules. For instance, peptidases hydrolyze peptide bonds in proteins, lipases break down lipids, and nucleases cleave nucleic acids. An example is the enzyme trypsin, a peptidase that cleaves peptide bonds at the carboxyl side of lysine or arginine residues. The reaction involves the incorporation of water, resulting in the formation of two separate fragments. Hydrolyases are crucial for digestion, cellular metabolism, and the recycling of biomolecules.

What is the function of ligases in DNA replication?

Ligases play a critical role in DNA replication by catalyzing the covalent joining of DNA fragments. DNA ligase, for example, is essential for sealing nicks in the DNA backbone, which occur during the replication process. This enzyme uses energy from ATP to form a phosphodiester bond between the 3'-hydroxyl end of one nucleotide and the 5'-phosphate end of another. This action is crucial for creating a continuous DNA strand from Okazaki fragments on the lagging strand. Without ligases, the DNA replication process would be incomplete, leading to fragmented and non-functional DNA molecules.