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Enzyme Catalysis - Characteristics and Roles of Enzymes, Mechanism of Enzyme Catalysis and Mode of Action of Enzymes

Have you ever wondered how wine is made?


The sucrose in grapes is broken down into glucose and fructose by the yeast enzyme 'Invertase.' The resulting glucose is converted into ethyl alcohol (wine) and carbon dioxide by the enzyme ‘Zymase’ .

If you keep milk overnight, it gets converted into curd. Lactobacillus converts milk to curd. 


To stop or slow down the environmental degradation caused by plastics, a bacterial enzyme that breaks down polymeric plastic into monomeric molecules is used.

The CRISPR-Cas9 enzyme is a well-known gene-editing enzyme.

Many of these enzyme-catalysed phenomena can be found all around us. Let's go deep into the enzymes to learn more about them.

TABLE OF CONTENTS 

  • What are Enzymes?
  • Characteristics of Enzymes
  • Role of Enzymes
  • What is Enzyme Catalysis?
  • Mechanism of Enzyme Catalysis
  • Examples of Enzyme-Catalysed Reactions
  • Mode of Enzyme Action
  • Practice Problems
  • Frequently Asked Questions - FAQ

What are Enzymes?


Enzymes are substances present in living organisms that enhance the rate of a chemical reaction. Enzymes are also known as biocatalysts, as they regulate all the biological processes that occur within living organisms. Without the presence of enzymes, many of the chemical reactions in the body will never achieve the expected conversion rate. Enzymes are proteins with high molecular mass ranging from 15000 to 1000000 g mol-1. The increase rates by 108 to 1020 times. The metabolic processes catalysed by enzymes include both anabolic and catabolic reactions. 

Example: The process of breakdown of complex molecules into small, easily digestible bits is possible because of the catalytic activity of enzymes. 

  • Amylase is a type of enzyme that breaks down complex carbohydrates into maltose. 
  • Lipase, generally formed in pancreas, is a digestive enzyme that breaks down fats into glycerol, fatty acids and other alcohols.
  • Protease is a type of enzyme breaks down proteins into amino acids. This enzyme is also formed in pancreas.

Enzymes play a pivotal role in regulating the body’s metabolism. So, the absence of any one enzyme in the system can lead to fatal conditions. 

Example: Phenylketonuria is an inherited metabolic disorder caused due to the deficiency of the enzyme Phenylalanine Hydroxylase. The condition is associated with intellectual disabilities.

Characteristics of Enzymes

1. High efficiency: Due to their high efficiency, even a single molecule of enzyme can convert millions of reactants to products per second.

2. High specificity: Every set of biochemical reactions in the body has specific enzymes. And only these enzymes can bring about the conversion. In other words, enzymes are highly specific i.e. the enzyme used to catalyse one biochemical reaction cannot be used for any other biochemical reactions.

3. Temperature dependence: The rate of an enzyme reaction becomes maximum at a definite temperature known as optimum temperature. On either side of the optimum temperature, the enzyme activity decreases. The optimum temperature range for enzymatic activity is 298 - 310 K. Human body temperature suitable for enzyme-catalysed reactions is 310 K.

4. pH dependence: The rate of an enzyme-catalysed reaction is maximum at a particular pH known as optimum pH. The Optimum pH range for enzyme-catalysed reactions lies between 5 - 7. 

5. Presence of co-enzymes and activators: The enzymatic activity is increased in the presence of certain substances, known as co-enzymes. These are non-protein organic molecules. 

Example: Vitamin.

Activators enhance the activity of an enzyme, whereas inhibitors reduce the activity. 

Example: Chloride ions act as an activator for the enzyme amylase. 

1. Influence of inhibitors and poisons: The inhibitors or poisons interact with the active functional groups on the enzyme surface, reducing or completely destroying the enzymes' catalytic activity. Many drugs are used because they act as enzyme inhibitors in the body.

Role of Enzymes

Apart from regulating the chemical reactions in living organisms, enzymes also have many commercial applications. These include

1. Enzymes play a key role in the fermentation industry in brewing wine, beer, and cheese making.

2. They are used in the production of biopolymers.

3. They are used in the field of medicine, to kill pathogenic microorganisms.

4. Proteolytic and lipolytic enzymes are also used in the tanning of leather.

What is Enzyme Catalysis? 

The process of enzymes binding to a particular subunit of a substrate and subsequently increasing its conversion rate to products is called enzyme catalysis. The site of the enzyme that interacts with the substrate is called the active site. To bring about the catalysis of a reaction, the enzyme may at times interact with the cofactors or coenzymes. It is important to note that the enzyme enhances the rate of both forward and backward reactions, thus maintaining the chemical equilibrium of the system.

Mechanism of Enzyme Catalysis

There are a number of cavities present on the surface of enzymes. They are usually the active centres on the surface of enzyme particles. The reactant molecules which have the complementary shape fit into these cavities just like a key fits into a lock. The activated complex thus formed, decomposes into products.


The process of catalysis brought about by enzymes is similar to the chemical catalysts used in the laboratory. The enzymes are recycled after the completion of every set of conversions. Enzymes bring about the fast conversion of substrates to products by lowering the activation energy. This energy is the barrier that needs to be crossed by the substrates to finally be converted to products. At the activation energy, the substrates are in the transition state and only move further in the reaction on receiving a sufficient amount of energy. The steps involved in the process of enzyme catalysis are:

1. Enzymes attract the substrate molecules towards their catalytic site and form an enzyme-substrate complex. 

E + S ES≠

Where

E: Enzyme
S: Substrate
ES≠: Activated complex

The substrates and enzymes are held together by non-covalent interactions. Based on the number of substrates involved, the complex formed can be binary, ternary and so on. This enzyme-substrate complex, later on achieving sufficient energy, crosses the activation energy barrier.

2. The enzyme causes the substrates to interact with each other at the catalytic site, thus promoting the formation of the product. After the product is formed, the enzyme dissociates and is recycled for the next round of chemical conversion. 

ES E + P 

Where
E: Enzyme
P: Product
ES≠: Activated complex


Examples of Enzyme Catalysed Reactions

1. Inversion of cane sugar: Sugar decomposes to give glucose and frcutose in presence of Invertase.


2. Conversion of glucose into ethyl alcohol: Glucose decomposes to give ethanol and carbondixode gas in presence of Zymase.


3. Conversion of milk into curd: Milk gets convert into curd by the enzyme lactobacilli. 


Mode of Enzyme Action

There are four ways in which the enzymes lower the activation energy and increase the rate of a reaction.

1. Space: Enzymes bring the substrates in close proximity, thus promoting their interaction.

2. Orientation: Enzymes bring about the proper orientation of the catalytic groups of the substrates on their active site.

3. Stabilised interaction: As most enzymes are made up of proteins, they provide their amino acid groups to the transient intermediates formed, thus stabilising their structure.

4. Restricted mobility: As substrates interact on the enzyme's active site, the movement of substrates is restricted, thus increasing the probability of interaction and formation of products. Enzyme catalysis is the process of enhancing the rate of any biochemical reaction occurring in the cells of a living organism.

Practice Problems

Q 1. What is the optimum temperature and pH for the proper functioning of enzymes in our body?

a. 37˚C and 7.35
b. 36˚C and 7.4
c. 35˚C and 8
d. 37˚C and 7.4

Answer: Enzymes can function efficiently under specific conditions called the optimum temperature and pH. For the proper functioning of enzymes in our body, the optimum temperature is 37˚C and the optimum pH is 7.35.

So, option A) is the correct answer.

Q 2. Which of the following enzymes catalyse the conversion of sucrose (present in the grapes) into glucose and fructose?

a. Invertase
b. Amylase
c. Lactobacillus
d. None of the above

Answer: The conversion of sucrose, present in grapes, into glucose and fructose is catalysed by the enzyme ‘Invertase’ present in yeast. 

So, option A) is the correct answer. 

Q 3. Enzymes are made of:

a. Large number of chains of amino acid
b. Large number of chains of carbohydrates
c. Both A and B
d. None of the above

Answer: Enzyme molecules are composed of a large proteins constituting one or more amino acid chains called polypeptide chains.The amino acid sequence dictates the protein's structure's distinctive folding patterns, which is critical for enzyme specificity.

So, option A) is the correct answer.

Q 4. Which of the following statements is true regarding enzymes?

a. Enzyme catalysis enhances the rate of any biochemical reaction
b. Enzyme promotes the formation of the product by letting the substrates to interact
c. Enzymes are highly specific in nature
d. All of the above

Answer: Enzyme catalysis is the process of enhancing the rate of any biochemical reaction occurring in the cells of a living organism. Enzyme causes the substrates to interact with each other at the catalytic site, thus promoting the formation of the product. Every set of biochemical reactions in the body has specific enzymes. And only these enzymes can bring about the conversion.

So, option D) is the correct answer.

Frequently Asked Questions - FAQ

Q 1. What are enzymes made of?
Answer: Enzymes are proteinic in nature; however, there is a small class of RNA enzymes known as ribozymes.

Q 2. What is a role of amylase in our body?
Answer: Amylase is an enzyme that catalyses the hydrolysis of starch into sugars. The pancreas and salivary gland make amylase to hydrolyse dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply energy to body. Starch is a stored form of food and a polysaccharide comprising glucose monomers.

Q 3. Are there any inhibhitors present in our body?
Answer: Generally, inhibitors are not present in our body, we take them as drugs to control the action of some enzymes many drugs are used as enzyme inhibitors in the body. 

Q 4. Give one example of enzyme present in our body?
Answer: Trypsin is the enzyme found in the small intestine, which is responsible for breaking proteins into amino acids.

Q 5. What are catabolic reactions?
Answer: Catabolism is a term used to describe a set of metabolic pathways involved in the breakdown of macromolecules into smaller molecules or monomers. Complex compounds are broken down into simpler molecules that can be used as building blocks for other molecules needed by cells, such as glycogen, proteins, and triglycerides. A small percentage of these molecules are simply broken down into waste products, which is a different approach of obtaining useable energy. The following are examples of catabolic processes: Cycle of citric acid, glycolysis, lipolysis, deamination by oxidation, breakdown of muscle tissue.

Q 6. What are anabolic reactions?
Answer: Anabolism is a series of enzyme-catalysed reactions in which nutrients are used to make relatively complex molecules with moderately simpler structures in living cells. Biosynthesis is a term used to describe the process of anabolism. The process involves the creation of cell components such as proteins, carbohydrates, and lipids, all of which require energy in the form of ATP (adenosine triphosphate), an energy-rich substance. These chemicals are created during catabolism, which is a breakdown process. Catabolic reactions are controlled by anabolic processes in developing cells. In non-growing cells, there is a balance between the two. 

Q 7. What are cofactors?
Answer: To act as an enzyme, certain enzymes require the inclusion of another non-protein molecule. These are referred to as cofactors. The enzyme becomes an active "holoenzyme" after the cofactor is introduced. Cofactors can be ions like zinc and iron ions or organic compounds like vitamins and vitamin-derived substances. Many of these cofactors will bind to the substrate at the binding site, making it easier for the substrate to bind to the enzyme. Cofactors are classified as "prosthetic groups" or "coenzymes" based on how closely they are connected to the enzyme; coenzymes bind more loosely to the enzyme and are thus modified during the enzymatic process, whereas prosthetic groups bind more tightly and are not modified.

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