Enzyme Catalysis - Definition, Characteristics, Mechanism, Examples

Catalysis is a phenomenon in which the rate of a reaction is changed by using a substance known as a catalyst. A catalyst is a substance that is used to change the rate of a reaction. Enzymes are a type of catalyst that is responsible for facilitating and speeding up many important biochemical reactions in plants and animals. Enzyme catalysis refers to catalysis in which enzymes act as a catalyst.

Enzymes are nitrogenous organic compounds that are complex and are produced by living plants and animals. They are high-molecular-mass protein molecules that form colloidal solutions in water. They are extremely effective catalysts, catalyzing a wide range of reactions, particularly those related to natural processes. Enzymes catalyze a variety of reactions that occur in the bodies of animals and plants in order to sustain life. As a result, the enzymes are referred to as biochemical catalysts, and the phenomenon is known as biochemical catalysis.

What is Enzyme catalysis?

Enzymes are proteins that can reduce the activation energy of a wide range of biological processes. They do this by attaching the reactant(s), also known as the substrate(s), to an enzyme's active site. The substrate(s) can form an activated complex at a lower energy level at the active site. When the reaction is finished, the product(s) exit the active site, allowing the enzyme to catalyze other reactions. The active site of an enzyme catalyzes a biological process by binding to a substrate. The products are released when the reaction has completed, and the enzyme can now catalyze more reactions.

Wide applicability, mild reaction conditions required for complex and chemically unstable molecules, low catalyst loading, good and effective reusability of biocatalyst, desired biodegradability of the enzyme (catalyst) to promote green chemistry, safe and ecofriendly nature, the ability to reduce or eliminate reaction by-products, and carrying out a conventional multistage reaction via single stag.

Characteristics of Enzyme catalysis

• A single enzyme catalyst molecule can convert up to a million molecules of reactant per second. As a result, enzyme catalysts are said to be extremely efficient.
• These biochemical catalysts are specific to specific types of reactions, which means that the same catalyst cannot be used in more than one reaction.
• A catalyst's effectiveness is greatest at its optimum temperature. At either end of the temperature range, the activity of the biochemical catalysts decreases.
• The pH of the solution affects biochemical catalysis. A catalyst performs best when the pH is between 5-7.
• In the presence of a coenzyme or an activator, such as sodium, the activity of the enzymes usually increases. The presence of a weak bond between the enzyme and a metal ion increases the rate of the reaction.
• Enzymes, like other catalysts, are inhibited or poisoned by the presence of certain substances. Inhibitors or poisons interact with the active functional groups on the enzyme surface, reducing or completely destroying the enzyme's catalytic activity. Many drugs are used because they act as enzyme inhibitors in the body.

Mechanism of an Enzyme catalyst

Enzymes are made up of a number of cavities on their outer surface. These cavities contain groups such as -COOH, -SH, and so on. These are referred to as the biochemical particle's activity centers. The substrate, which has the opposite charge as the enzyme, fits into the cavities in the same way that a key fits into a lock. Because of the presence of active groups, the formed complex decomposes to give the products. As a result, this occurs in two steps:

Step 1: Combination of enzyme and reactant

Step 2: The complex molecule is disintegrated to yield the product.

Examples of enzyme-catalyzed reactions

• Inversion of cane sugar: Cane sugar is converted into glucose and fructose by the invertase enzyme.
• Conversion of glucose into ethyl alcohol: The zymase enzyme breaks down glucose to produce ethyl alcohol and carbon dioxide.
• Conversion of starch into maltose: Diastase is an enzyme that converts starch to maltose.
• Conversion of maltose into glucose: Maltase is an enzyme that converts maltose to glucose.
• Decomposition of urea into ammonia and carbon dioxide: This decomposition is catalyzed by the enzyme urease.
• In the stomach, the pepsin enzyme hydrolyzes proteins to form peptides, whereas, in the intestine, pancreatic trypsin hydrolyzes proteins to form amino acids.
• Conversion of milk to curd: This is an enzymatic reaction caused by the lactobacilli enzyme found in curd.

Catalysis in Industry

Haber’s process to manufacture ammonia

The Haber process is one of the most efficient and successful industrial procedures for producing ammonia. Carl Bosch took the design and created a machine for industrial-level production in 1910. The Haber process is a good case study for showing how industrial chemists use their knowledge of the factors that affect chemical equilibrium to find the best conditions for producing a high yield of products at a reasonable rate.

The Haber process converts atmospheric nitrogen (N₂) to ammonia (NH₃) by reacting it with hydrogen (H₂). A metal catalyst is used in this case, and high temperatures and pressures are maintained.

N₂ (g) + 3H₂ (g) ⇢ 2NH₃ (g)

Ostwald’s process to manufacture Nitric acid

The process of converting ammonia to nitric acid is simply oxidation. This specific oxidation reaction produces the corresponding nitric oxide. Furthermore, when nitric oxide is oxidized, nitrous gases are formed, which can trap water molecules. As a result, nitric acid is produced. Where ammonia will give rise to the product, catalytic oxidation with O₂ is used. 

There are specific reaction chambers in the process where ammonia is fed from one direction and the air is fed from the other. There is also the possibility of negative side effects. Other reactions will occur if we proceed with the ammonia oxidation. It is most common in the case of dinitrogen. Ammonia is produced when dinitrogen is removed. If we try to oxidize the ammonia, we will get the dinitrogen back. Other oxidized forms are possible.

In all of these cases, optimizing the reaction conditions is critical; otherwise, many gases can be formed alongside the desired NO. As a result, it is critical to avoid side effects. The following stage involves the oxidation of NO₂, which can also dimerize to yield N₂O₄. At this stage, the reaction is only favored at low temperatures.

Contact process to manufacture Sulphuric acid

The contact process is a modern method for producing concentrated sulfuric acid that is used by industries. Sulfur dioxide and oxygen are passed over a hot catalyst during this process (V₂O₅). They combine to form sulphur trioxide, which reacts with water to form sulfuric acid.

Sample Questions 

Question 1: How is ammonia manufactured by Haber’s process?

Answer:

Ammonia production via the Haber cycle. The nitrogen and hydrogen Haber cycles are major sources of it. The Haber process converts nitrogen gas from the atmosphere into ammonia gas by combining it with molecular hydrogen gas.

Question 2: How do we get hydrogen for the Haber process?

Answer:

The main source of hydrogen is methane from natural gas. Steam reforming is a process that separates the carbon and hydrogen atoms in natural gas in a high-temperature and high-pressure pipe inside a reformer with a nickel catalyst.

Question 3: What factors affect the Haber process?

Answer:

As the Haber cycle is a reversible reaction, the yield of ammonia can be changed by increasing the pressure or temperature of the reaction. Ammonia yield increases as reaction pressure is increased.

Question 4: What is the contact process?

Answer:

The contact process is a modern method for producing concentrated sulfuric acid that is used by industries. Sulfur dioxide and oxygen are passed over a hot catalyst during this process. They combine to form sulphur trioxide, which reacts with water to form sulfuric acid.

Question 5: What is the mechanism of enzyme catalyst? 

Answer:

Enzymes are made up of a number of cavities on their outer surface. These cavities contain groups such as -COOH, -SH, and so on. These are referred to as the biochemical particle's active centres. The substrate, which has the opposite charge as the enzyme, fits into the cavities in the same way that a key fits into a lock. Because of the presence of active groups, the formed complex decomposes to give the products. As a result, this occurs in two steps:

• Combination of enzyme and reactant
• The complex molecule is disintegrated to yield the product.